Merge branch 'master' of github.com:git/git

* 'master' of github.com:git/git: (63 commits)
  Git 2.31-rc1
  Hopefully the last batch before -rc1
  Revert "commit-graph: when incompatible with graphs, indicate why"
  read-cache: make the index write buffer size 128K
  dir: fix malloc of root untracked_cache_dir
  commit-graph.c: display correct number of chunks when writing
  doc/reftable: document how to handle windows
  fetch-pack: print and use dangling .gitmodules
  fetch-pack: with packfile URIs, use index-pack arg
  http-fetch: allow custom index-pack args
  http: allow custom index-pack args
  chunk-format: add technical docs
  chunk-format: restore duplicate chunk checks
  midx: use 64-bit multiplication for chunk sizes
  midx: use chunk-format read API
  commit-graph: use chunk-format read API
  chunk-format: create read chunk API
  midx: use chunk-format API in write_midx_internal()
  midx: drop chunk progress during write
  midx: return success/failure in chunk write methods
  ...

48 files changed, 1948 insertions, 924 deletions

diff --git a/Documentation/RelNotes/2.31.0.txt b/Documentation/RelNotes/2.31.0.txt
index ef8b0d158e..04bd5b70a9 100644
--- a/Documentation/RelNotes/2.31.0.txt
+++ b/Documentation/RelNotes/2.31.0.txt
@@ -197,6 +197,31 @@ Performance, Internal Implementation, Development Support etc.
  * The code to implement "git merge-base --independent" was poorly
    done and was kept from the very beginning of the feature.
 
+ * Preliminary changes to fsmonitor integration.
+
+ * Performance optimization work on the rename detection continues.
+
+ * The common code to deal with "chunked file format" that is shared
+   by the multi-pack-index and commit-graph files have been factored
+   out, to help codepaths for both filetypes to become more robust.
+
+ * The approach to "fsck" the incoming objects in "index-pack" is
+   attractive for performance reasons (we have them already in core,
+   inflated and ready to be inspected), but fundamentally cannot be
+   applied fully when we receive more than one pack stream, as a tree
+   object in one pack may refer to a blob object in another pack as
+   ".gitmodules", when we want to inspect blobs that are used as
+   ".gitmodules" file, for example.  Teach "index-pack" to emit
+   objects that must be inspected later and check them in the calling
+   "fetch-pack" process.
+
+ * The logic to handle "trailer" related placeholders in the
+   "--format=" mechanisms in the "log" family and "for-each-ref"
+   family is getting unified.
+
+ * Raise the buffer size used when writing the index file out from
+   (obviously too small) 8kB to (clearly sufficiently large) 128kB.
+
 
 Fixes since v2.30
 -----------------
@@ -318,6 +343,12 @@ Fixes since v2.30
    corrected.
    (merge 20e416409f jc/push-delete-nothing later to maint).
 
+ * Test script modernization.
+   (merge 488acf15df sv/t7001-modernize later to maint).
+
+ * An under-allocation for the untracked cache data has been corrected.
+   (merge 6347d649bc jh/untracked-cache-fix later to maint).
+
  * Other code cleanup, docfix, build fix, etc.
    (merge e3f5da7e60 sg/t7800-difftool-robustify later to maint).
    (merge 9d336655ba js/doc-proto-v2-response-end later to maint).
diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index 2962f85a50..2ae2478de7 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -260,11 +260,9 @@ contents:lines=N::
 	The first `N` lines of the message.
 
 Additionally, the trailers as interpreted by linkgit:git-interpret-trailers[1]
-are obtained as `trailers` (or by using the historical alias
-`contents:trailers`).  Non-trailer lines from the trailer block can be omitted
-with `trailers:only`. Whitespace-continuations can be removed from trailers so
-that each trailer appears on a line by itself with its full content with
-`trailers:unfold`. Both can be used together as `trailers:unfold,only`.
+are obtained as `trailers[:options]` (or by using the historical alias
+`contents:trailers[:options]`). For valid [:option] values see `trailers`
+section of linkgit:git-log[1].
 
 For sorting purposes, fields with numeric values sort in numeric order
 (`objectsize`, `authordate`, `committerdate`, `creatordate`, `taggerdate`).
diff --git a/Documentation/git-http-fetch.txt b/Documentation/git-http-fetch.txt
index 4deb4893f5..9fa17b60e4 100644
--- a/Documentation/git-http-fetch.txt
+++ b/Documentation/git-http-fetch.txt
@@ -41,11 +41,17 @@ commit-id::
 		<commit-id>['\t'<filename-as-in--w>]
 
 --packfile=<hash>::
-	Instead of a commit id on the command line (which is not expected in
+	For internal use only. Instead of a commit id on the command
+	line (which is not expected in
 	this case), 'git http-fetch' fetches the packfile directly at the given
 	URL and uses index-pack to generate corresponding .idx and .keep files.
 	The hash is used to determine the name of the temporary file and is
-	arbitrary. The output of index-pack is printed to stdout.
+	arbitrary. The output of index-pack is printed to stdout. Requires
+	--index-pack-args.
+
+--index-pack-args=<args>::
+	For internal use only. The command to run on the contents of the
+	downloaded pack. Arguments are URL-encoded separated by spaces.
 
 --recover::
 	Verify that everything reachable from target is fetched.  Used after
diff --git a/Documentation/git-index-pack.txt b/Documentation/git-index-pack.txt
index 69ba904d44..7fa74b9e79 100644
--- a/Documentation/git-index-pack.txt
+++ b/Documentation/git-index-pack.txt
@@ -86,7 +86,12 @@ OPTIONS
 	Die if the pack contains broken links. For internal use only.
 
 --fsck-objects::
-	Die if the pack contains broken objects. For internal use only.
+	For internal use only.
++
+Die if the pack contains broken objects. If the pack contains a tree
+pointing to a .gitmodules blob that does not exist, prints the hash of
+that blob (for the caller to check) after the hash that goes into the
+name of the pack/idx file (see "Notes").
 
 --threads=<n>::
 	Specifies the number of threads to spawn when resolving
diff --git a/Documentation/gitdiffcore.txt b/Documentation/gitdiffcore.txt
index 2bd1220477..1c7269655f 100644
--- a/Documentation/gitdiffcore.txt
+++ b/Documentation/gitdiffcore.txt
@@ -169,6 +169,26 @@ a similarity score different from the default of 50% by giving a
 number after the "-M" or "-C" option (e.g. "-M8" to tell it to use
 8/10 = 80%).
 
+Note that when rename detection is on but both copy and break
+detection are off, rename detection adds a preliminary step that first
+checks if files are moved across directories while keeping their
+filename the same.  If there is a file added to a directory whose
+contents is sufficiently similar to a file with the same name that got
+deleted from a different directory, it will mark them as renames and
+exclude them from the later quadratic step (the one that pairwise
+compares all unmatched files to find the "best" matches, determined by
+the highest content similarity).  So, for example, if a deleted
+docs/ext.txt and an added docs/config/ext.txt are similar enough, they
+will be marked as a rename and prevent an added docs/ext.md that may
+be even more similar to the deleted docs/ext.txt from being considered
+as the rename destination in the later step.  For this reason, the
+preliminary "match same filename" step uses a bit higher threshold to
+mark a file pair as a rename and stop considering other candidates for
+better matches.  At most, one comparison is done per file in this
+preliminary pass; so if there are several remaining ext.txt files
+throughout the directory hierarchy after exact rename detection, this
+preliminary step will be skipped for those files.
+
 Note.  When the "-C" option is used with `--find-copies-harder`
 option, 'git diff-{asterisk}' commands feed unmodified filepairs to
 diffcore mechanism as well as modified ones.  This lets the copy
diff --git a/Documentation/technical/chunk-format.txt b/Documentation/technical/chunk-format.txt
new file mode 100644
index 0000000000..593614fced
--- /dev/null
+++ b/Documentation/technical/chunk-format.txt
@@ -0,0 +1,116 @@
+Chunk-based file formats
+========================
+
+Some file formats in Git use a common concept of "chunks" to describe
+sections of the file. This allows structured access to a large file by
+scanning a small "table of contents" for the remaining data. This common
+format is used by the `commit-graph` and `multi-pack-index` files. See
+link:technical/pack-format.html[the `multi-pack-index` format] and
+link:technical/commit-graph-format.html[the `commit-graph` format] for
+how they use the chunks to describe structured data.
+
+A chunk-based file format begins with some header information custom to
+that format. That header should include enough information to identify
+the file type, format version, and number of chunks in the file. From this
+information, that file can determine the start of the chunk-based region.
+
+The chunk-based region starts with a table of contents describing where
+each chunk starts and ends. This consists of (C+1) rows of 12 bytes each,
+where C is the number of chunks. Consider the following table:
+
+  | Chunk ID (4 bytes) | Chunk Offset (8 bytes) |
+  |--------------------|------------------------|
+  | ID[0]              | OFFSET[0]              |
+  | ...                | ...                    |
+  | ID[C]              | OFFSET[C]              |
+  | 0x0000             | OFFSET[C+1]            |
+
+Each row consists of a 4-byte chunk identifier (ID) and an 8-byte offset.
+Each integer is stored in network-byte order.
+
+The chunk identifier `ID[i]` is a label for the data stored within this
+fill from `OFFSET[i]` (inclusive) to `OFFSET[i+1]` (exclusive). Thus, the
+size of the `i`th chunk is equal to the difference between `OFFSET[i+1]`
+and `OFFSET[i]`. This requires that the chunk data appears contiguously
+in the same order as the table of contents.
+
+The final entry in the table of contents must be four zero bytes. This
+confirms that the table of contents is ending and provides the offset for
+the end of the chunk-based data.
+
+Note: The chunk-based format expects that the file contains _at least_ a
+trailing hash after `OFFSET[C+1]`.
+
+Functions for working with chunk-based file formats are declared in
+`chunk-format.h`. Using these methods provide extra checks that assist
+developers when creating new file formats.
+
+Writing chunk-based file formats
+--------------------------------
+
+To write a chunk-based file format, create a `struct chunkfile` by
+calling `init_chunkfile()` and pass a `struct hashfile` pointer. The
+caller is responsible for opening the `hashfile` and writing header
+information so the file format is identifiable before the chunk-based
+format begins.
+
+Then, call `add_chunk()` for each chunk that is intended for write. This
+populates the `chunkfile` with information about the order and size of
+each chunk to write. Provide a `chunk_write_fn` function pointer to
+perform the write of the chunk data upon request.
+
+Call `write_chunkfile()` to write the table of contents to the `hashfile`
+followed by each of the chunks. This will verify that each chunk wrote
+the expected amount of data so the table of contents is correct.
+
+Finally, call `free_chunkfile()` to clear the `struct chunkfile` data. The
+caller is responsible for finalizing the `hashfile` by writing the trailing
+hash and closing the file.
+
+Reading chunk-based file formats
+--------------------------------
+
+To read a chunk-based file format, the file must be opened as a
+memory-mapped region. The chunk-format API expects that the entire file
+is mapped as a contiguous memory region.
+
+Initialize a `struct chunkfile` pointer with `init_chunkfile(NULL)`.
+
+After reading the header information from the beginning of the file,
+including the chunk count, call `read_table_of_contents()` to populate
+the `struct chunkfile` with the list of chunks, their offsets, and their
+sizes.
+
+Extract the data information for each chunk using `pair_chunk()` or
+`read_chunk()`:
+
+* `pair_chunk()` assigns a given pointer with the location inside the
+  memory-mapped file corresponding to that chunk's offset. If the chunk
+  does not exist, then the pointer is not modified.
+
+* `read_chunk()` takes a `chunk_read_fn` function pointer and calls it
+  with the appropriate initial pointer and size information. The function
+  is not called if the chunk does not exist. Use this method to read chunks
+  if you need to perform immediate parsing or if you need to execute logic
+  based on the size of the chunk.
+
+After calling these methods, call `free_chunkfile()` to clear the
+`struct chunkfile` data. This will not close the memory-mapped region.
+Callers are expected to own that data for the timeframe the pointers into
+the region are needed.
+
+Examples
+--------
+
+These file formats use the chunk-format API, and can be used as examples
+for future formats:
+
+* *commit-graph:* see `write_commit_graph_file()` and `parse_commit_graph()`
+  in `commit-graph.c` for how the chunk-format API is used to write and
+  parse the commit-graph file format documented in
+  link:technical/commit-graph-format.html[the commit-graph file format].
+
+* *multi-pack-index:* see `write_midx_internal()` and `load_multi_pack_index()`
+  in `midx.c` for how the chunk-format API is used to write and
+  parse the multi-pack-index file format documented in
+  link:technical/pack-format.html[the multi-pack-index file format].
diff --git a/Documentation/technical/commit-graph-format.txt b/Documentation/technical/commit-graph-format.txt
index b6658eff18..87971c27dd 100644
--- a/Documentation/technical/commit-graph-format.txt
+++ b/Documentation/technical/commit-graph-format.txt
@@ -61,6 +61,9 @@ CHUNK LOOKUP:
       the length using the next chunk position if necessary.) Each chunk
       ID appears at most once.
 
+  The CHUNK LOOKUP matches the table of contents from
+  link:technical/chunk-format.html[the chunk-based file format].
+
   The remaining data in the body is described one chunk at a time, and
   these chunks may be given in any order. Chunks are required unless
   otherwise specified.
diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt
index 8833b71c8b..1faa949bf6 100644
--- a/Documentation/technical/pack-format.txt
+++ b/Documentation/technical/pack-format.txt
@@ -336,6 +336,9 @@ CHUNK LOOKUP:
 	    (Chunks are provided in file-order, so you can infer the length
 	    using the next chunk position if necessary.)
 
+	The CHUNK LOOKUP matches the table of contents from
+	link:technical/chunk-format.html[the chunk-based file format].
+
 	The remaining data in the body is described one chunk at a time, and
 	these chunks may be given in any order. Chunks are required unless
 	otherwise specified.
diff --git a/Documentation/technical/reftable.txt b/Documentation/technical/reftable.txt
index 8095ab2590..3ef169af27 100644
--- a/Documentation/technical/reftable.txt
+++ b/Documentation/technical/reftable.txt
@@ -872,17 +872,11 @@ A repository must set its `$GIT_DIR/config` to configure reftable:
 Layout
 ^^^^^^
 
-A collection of reftable files are stored in the `$GIT_DIR/reftable/`
-directory:
-
-....
-00000001-00000001.log
-00000002-00000002.ref
-00000003-00000003.ref
-....
-
-where reftable files are named by a unique name such as produced by the
-function `${min_update_index}-${max_update_index}.ref`.
+A collection of reftable files are stored in the `$GIT_DIR/reftable/` directory.
+Their names should have a random element, such that each filename is globally
+unique; this helps avoid spurious failures on Windows, where open files cannot
+be removed or overwritten. It suggested to use
+`${min_update_index}-${max_update_index}-${random}.ref` as a naming convention.
 
 Log-only files use the `.log` extension, while ref-only and mixed ref
 and log files use `.ref`. extension.
@@ -893,9 +887,9 @@ current files, one per line, in order, from oldest (base) to newest
 
 ....
 $ cat .git/reftable/tables.list
-00000001-00000001.log
-00000002-00000002.ref
-00000003-00000003.ref
+00000001-00000001-RANDOM1.log
+00000002-00000002-RANDOM2.ref
+00000003-00000003-RANDOM3.ref
 ....
 
 Readers must read `$GIT_DIR/reftable/tables.list` to determine which
@@ -940,7 +934,7 @@ new reftable and atomically appending it to the stack:
 3.  Select `update_index` to be most recent file's
 `max_update_index + 1`.
 4.  Prepare temp reftable `tmp_XXXXXX`, including log entries.
-5.  Rename `tmp_XXXXXX` to `${update_index}-${update_index}.ref`.
+5.  Rename `tmp_XXXXXX` to `${update_index}-${update_index}-${random}.ref`.
 6.  Copy `tables.list` to `tables.list.lock`, appending file from (5).
 7.  Rename `tables.list.lock` to `tables.list`.
 
@@ -993,7 +987,7 @@ prevents other processes from trying to compact these files.
 should always be the case, assuming that other processes are adhering to
 the locking protocol.
 7.  Rename `${min_update_index}-${max_update_index}_XXXXXX` to
-`${min_update_index}-${max_update_index}.ref`.
+`${min_update_index}-${max_update_index}-${random}.ref`.
 8.  Write the new stack to `tables.list.lock`, replacing `B` and `C`
 with the file from (4).
 9.  Rename `tables.list.lock` to `tables.list`.
@@ -1005,6 +999,22 @@ This strategy permits compactions to proceed independently of updates.
 Each reftable (compacted or not) is uniquely identified by its name, so
 open reftables can be cached by their name.
 
+Windows
+^^^^^^^
+
+On windows, and other systems that do not allow deleting or renaming to open
+files, compaction may succeed, but other readers may prevent obsolete tables
+from being deleted.
+
+On these platforms, the following strategy can be followed: on closing a
+reftable stack, reload `tables.list`, and delete any tables no longer mentioned
+in `tables.list`.
+
+Irregular program exit may still leave about unused files. In this case, a
+cleanup operation can read `tables.list`, note its modification timestamp, and
+delete any unreferenced `*.ref` files that are older.
+
+
 Alternatives considered
 ~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 6fb66d3e55..7b99fe5dc5 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -1,7 +1,7 @@
 #!/bin/sh
 
 GVF=GIT-VERSION-FILE
-DEF_VER=v2.31.0-rc0
+DEF_VER=v2.31.0-rc1
 
 LF='
 '
diff --git a/Makefile b/Makefile
index 9b1bde2e0e..dd08b4ced0 100644
--- a/Makefile
+++ b/Makefile
@@ -834,6 +834,7 @@ LIB_OBJS += bundle.o
 LIB_OBJS += cache-tree.o
 LIB_OBJS += chdir-notify.o
 LIB_OBJS += checkout.o
+LIB_OBJS += chunk-format.o
 LIB_OBJS += color.o
 LIB_OBJS += column.o
 LIB_OBJS += combine-diff.o
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 54f74c4874..bad5748807 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -1712,6 +1712,22 @@ static void show_pack_info(int stat_only)
 	}
 }
 
+static int print_dangling_gitmodules(struct fsck_options *o,
+				     const struct object_id *oid,
+				     enum object_type object_type,
+				     int msg_type, const char *message)
+{
+	/*
+	 * NEEDSWORK: Plumb the MSG_ID (from fsck.c) here and use it
+	 * instead of relying on this string check.
+	 */
+	if (starts_with(message, "gitmodulesMissing")) {
+		printf("%s\n", oid_to_hex(oid));
+		return 0;
+	}
+	return fsck_error_function(o, oid, object_type, msg_type, message);
+}
+
 int cmd_index_pack(int argc, const char **argv, const char *prefix)
 {
 	int i, fix_thin_pack = 0, verify = 0, stat_only = 0, rev_index;
@@ -1932,8 +1948,13 @@ int cmd_index_pack(int argc, const char **argv, const char *prefix)
 	else
 		close(input_fd);
 
-	if (do_fsck_object && fsck_finish(&fsck_options))
-		die(_("fsck error in pack objects"));
+	if (do_fsck_object) {
+		struct fsck_options fo = fsck_options;
+
+		fo.error_func = print_dangling_gitmodules;
+		if (fsck_finish(&fo))
+			die(_("fsck error in pack objects"));
+	}
 
 	free(objects);
 	strbuf_release(&index_name_buf);
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index b89ce31bf2..d26040c477 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -2275,7 +2275,7 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 		status = start_command(&child);
 		if (status)
 			return "index-pack fork failed";
-		pack_lockfile = index_pack_lockfile(child.out);
+		pack_lockfile = index_pack_lockfile(child.out, NULL);
 		close(child.out);
 		status = finish_command(&child);
 		if (status)
diff --git a/chunk-format.c b/chunk-format.c
new file mode 100644
index 0000000000..da191e59a2
--- /dev/null
+++ b/chunk-format.c
@@ -0,0 +1,179 @@
+#include "cache.h"
+#include "chunk-format.h"
+#include "csum-file.h"
+
+/*
+ * When writing a chunk-based file format, collect the chunks in
+ * an array of chunk_info structs. The size stores the _expected_
+ * amount of data that will be written by write_fn.
+ */
+struct chunk_info {
+	uint32_t id;
+	uint64_t size;
+	chunk_write_fn write_fn;
+
+	const void *start;
+};
+
+struct chunkfile {
+	struct hashfile *f;
+
+	struct chunk_info *chunks;
+	size_t chunks_nr;
+	size_t chunks_alloc;
+};
+
+struct chunkfile *init_chunkfile(struct hashfile *f)
+{
+	struct chunkfile *cf = xcalloc(1, sizeof(*cf));
+	cf->f = f;
+	return cf;
+}
+
+void free_chunkfile(struct chunkfile *cf)
+{
+	if (!cf)
+		return;
+	free(cf->chunks);
+	free(cf);
+}
+
+int get_num_chunks(struct chunkfile *cf)
+{
+	return cf->chunks_nr;
+}
+
+void add_chunk(struct chunkfile *cf,
+	       uint32_t id,
+	       size_t size,
+	       chunk_write_fn fn)
+{
+	ALLOC_GROW(cf->chunks, cf->chunks_nr + 1, cf->chunks_alloc);
+
+	cf->chunks[cf->chunks_nr].id = id;
+	cf->chunks[cf->chunks_nr].write_fn = fn;
+	cf->chunks[cf->chunks_nr].size = size;
+	cf->chunks_nr++;
+}
+
+int write_chunkfile(struct chunkfile *cf, void *data)
+{
+	int i;
+	uint64_t cur_offset = hashfile_total(cf->f);
+
+	/* Add the table of contents to the current offset */
+	cur_offset += (cf->chunks_nr + 1) * CHUNK_TOC_ENTRY_SIZE;
+
+	for (i = 0; i < cf->chunks_nr; i++) {
+		hashwrite_be32(cf->f, cf->chunks[i].id);
+		hashwrite_be64(cf->f, cur_offset);
+
+		cur_offset += cf->chunks[i].size;
+	}
+
+	/* Trailing entry marks the end of the chunks */
+	hashwrite_be32(cf->f, 0);
+	hashwrite_be64(cf->f, cur_offset);
+
+	for (i = 0; i < cf->chunks_nr; i++) {
+		off_t start_offset = hashfile_total(cf->f);
+		int result = cf->chunks[i].write_fn(cf->f, data);
+
+		if (result)
+			return result;
+
+		if (hashfile_total(cf->f) - start_offset != cf->chunks[i].size)
+			BUG("expected to write %"PRId64" bytes to chunk %"PRIx32", but wrote %"PRId64" instead",
+			    cf->chunks[i].size, cf->chunks[i].id,
+			    hashfile_total(cf->f) - start_offset);
+	}
+
+	return 0;
+}
+
+int read_table_of_contents(struct chunkfile *cf,
+			   const unsigned char *mfile,
+			   size_t mfile_size,
+			   uint64_t toc_offset,
+			   int toc_length)
+{
+	int i;
+	uint32_t chunk_id;
+	const unsigned char *table_of_contents = mfile + toc_offset;
+
+	ALLOC_GROW(cf->chunks, toc_length, cf->chunks_alloc);
+
+	while (toc_length--) {
+		uint64_t chunk_offset, next_chunk_offset;
+
+		chunk_id = get_be32(table_of_contents);
+		chunk_offset = get_be64(table_of_contents + 4);
+
+		if (!chunk_id) {
+			error(_("terminating chunk id appears earlier than expected"));
+			return 1;
+		}
+
+		table_of_contents += CHUNK_TOC_ENTRY_SIZE;
+		next_chunk_offset = get_be64(table_of_contents + 4);
+
+		if (next_chunk_offset < chunk_offset ||
+		    next_chunk_offset > mfile_size - the_hash_algo->rawsz) {
+			error(_("improper chunk offset(s) %"PRIx64" and %"PRIx64""),
+			      chunk_offset, next_chunk_offset);
+			return -1;
+		}
+
+		for (i = 0; i < cf->chunks_nr; i++) {
+			if (cf->chunks[i].id == chunk_id) {
+				error(_("duplicate chunk ID %"PRIx32" found"),
+					chunk_id);
+				return -1;
+			}
+		}
+
+		cf->chunks[cf->chunks_nr].id = chunk_id;
+		cf->chunks[cf->chunks_nr].start = mfile + chunk_offset;
+		cf->chunks[cf->chunks_nr].size = next_chunk_offset - chunk_offset;
+		cf->chunks_nr++;
+	}
+
+	chunk_id = get_be32(table_of_contents);
+	if (chunk_id) {
+		error(_("final chunk has non-zero id %"PRIx32""), chunk_id);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int pair_chunk_fn(const unsigned char *chunk_start,
+			 size_t chunk_size,
+			 void *data)
+{
+	const unsigned char **p = data;
+	*p = chunk_start;
+	return 0;
+}
+
+int pair_chunk(struct chunkfile *cf,
+	       uint32_t chunk_id,
+	       const unsigned char **p)
+{
+	return read_chunk(cf, chunk_id, pair_chunk_fn, p);
+}
+
+int read_chunk(struct chunkfile *cf,
+	       uint32_t chunk_id,
+	       chunk_read_fn fn,
+	       void *data)
+{
+	int i;
+
+	for (i = 0; i < cf->chunks_nr; i++) {
+		if (cf->chunks[i].id == chunk_id)
+			return fn(cf->chunks[i].start, cf->chunks[i].size, data);
+	}
+
+	return CHUNK_NOT_FOUND;
+}
diff --git a/chunk-format.h b/chunk-format.h
new file mode 100644
index 0000000000..9ccbe00377
--- /dev/null
+++ b/chunk-format.h
@@ -0,0 +1,68 @@
+#ifndef CHUNK_FORMAT_H
+#define CHUNK_FORMAT_H
+
+#include "git-compat-util.h"
+
+struct hashfile;
+struct chunkfile;
+
+#define CHUNK_TOC_ENTRY_SIZE (sizeof(uint32_t) + sizeof(uint64_t))
+
+/*
+ * Initialize a 'struct chunkfile' for writing _or_ reading a file
+ * with the chunk format.
+ *
+ * If writing a file, supply a non-NULL 'struct hashfile *' that will
+ * be used to write.
+ *
+ * If reading a file, use a NULL 'struct hashfile *' and then call
+ * read_table_of_contents(). Supply the memory-mapped data to the
+ * pair_chunk() or read_chunk() methods, as appropriate.
+ *
+ * DO NOT MIX THESE MODES. Use different 'struct chunkfile' instances
+ * for reading and writing.
+ */
+struct chunkfile *init_chunkfile(struct hashfile *f);
+void free_chunkfile(struct chunkfile *cf);
+int get_num_chunks(struct chunkfile *cf);
+typedef int (*chunk_write_fn)(struct hashfile *f, void *data);
+void add_chunk(struct chunkfile *cf,
+	       uint32_t id,
+	       size_t size,
+	       chunk_write_fn fn);
+int write_chunkfile(struct chunkfile *cf, void *data);
+
+int read_table_of_contents(struct chunkfile *cf,
+			   const unsigned char *mfile,
+			   size_t mfile_size,
+			   uint64_t toc_offset,
+			   int toc_length);
+
+#define CHUNK_NOT_FOUND (-2)
+
+/*
+ * Find 'chunk_id' in the given chunkfile and assign the
+ * given pointer to the position in the mmap'd file where
+ * that chunk begins.
+ *
+ * Returns CHUNK_NOT_FOUND if the chunk does not exist.
+ */
+int pair_chunk(struct chunkfile *cf,
+	       uint32_t chunk_id,
+	       const unsigned char **p);
+
+typedef int (*chunk_read_fn)(const unsigned char *chunk_start,
+			     size_t chunk_size, void *data);
+/*
+ * Find 'chunk_id' in the given chunkfile and call the
+ * given chunk_read_fn method with the information for
+ * that chunk.
+ *
+ * Returns CHUNK_NOT_FOUND if the chunk does not exist.
+ */
+int read_chunk(struct chunkfile *cf,
+	       uint32_t chunk_id,
+	       chunk_read_fn fn,
+	       void *data);
+
+#endif
diff --git a/commit-graph.c b/commit-graph.c
index 7a5f15b842..ca025ce8eb 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -19,6 +19,7 @@
 #include "shallow.h"
 #include "json-writer.h"
 #include "trace2.h"
+#include "chunk-format.h"
 
 void git_test_write_commit_graph_or_die(void)
 {
@@ -44,7 +45,6 @@ void git_test_write_commit_graph_or_die(void)
 #define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */
 #define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */
 #define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */
-#define MAX_NUM_CHUNKS 9
 
 #define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16)
 
@@ -59,8 +59,7 @@ void git_test_write_commit_graph_or_die(void)
 
 #define GRAPH_HEADER_SIZE 8
 #define GRAPH_FANOUT_SIZE (4 * 256)
-#define GRAPH_CHUNKLOOKUP_WIDTH 12
-#define GRAPH_MIN_SIZE (GRAPH_HEADER_SIZE + 4 * GRAPH_CHUNKLOOKUP_WIDTH \
+#define GRAPH_MIN_SIZE (GRAPH_HEADER_SIZE + 4 * CHUNK_TOC_ENTRY_SIZE \
 			+ GRAPH_FANOUT_SIZE + the_hash_algo->rawsz)
 
 #define CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW (1ULL << 31)
@@ -215,24 +214,16 @@ static int commit_graph_compatible(struct repository *r)
 
 	if (read_replace_refs) {
 		prepare_replace_object(r);
-		if (hashmap_get_size(&r->objects->replace_map->map)) {
-			warning(_("repository contains replace objects; "
-			       "skipping commit-graph"));
+		if (hashmap_get_size(&r->objects->replace_map->map))
 			return 0;
-		}
 	}
 
 	prepare_commit_graft(r);
 	if (r->parsed_objects &&
-	    (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent)) {
-		warning(_("repository contains (deprecated) grafts; "
-		       "skipping commit-graph"));
+	    (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent))
 		return 0;
-	}
-	if (is_repository_shallow(r)) {
-		warning(_("repository is shallow; skipping commit-graph"));
+	if (is_repository_shallow(r))
 		return 0;
-	}
 
 	return 1;
 }
@@ -306,15 +297,43 @@ static int verify_commit_graph_lite(struct commit_graph *g)
 	return 0;
 }
 
+static int graph_read_oid_lookup(const unsigned char *chunk_start,
+				 size_t chunk_size, void *data)
+{
+	struct commit_graph *g = data;
+	g->chunk_oid_lookup = chunk_start;
+	g->num_commits = chunk_size / g->hash_len;
+	return 0;
+}
+
+static int graph_read_bloom_data(const unsigned char *chunk_start,
+				  size_t chunk_size, void *data)
+{
+	struct commit_graph *g = data;
+	uint32_t hash_version;
+	g->chunk_bloom_data = chunk_start;
+	hash_version = get_be32(chunk_start);
+
+	if (hash_version != 1)
+		return 0;
+
+	g->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
+	g->bloom_filter_settings->hash_version = hash_version;
+	g->bloom_filter_settings->num_hashes = get_be32(chunk_start + 4);
+	g->bloom_filter_settings->bits_per_entry = get_be32(chunk_start + 8);
+	g->bloom_filter_settings->max_changed_paths = DEFAULT_BLOOM_MAX_CHANGES;
+
+	return 0;
+}
+
 struct commit_graph *parse_commit_graph(struct repository *r,
 					void *graph_map, size_t graph_size)
 {
-	const unsigned char *data, *chunk_lookup;
-	uint32_t i;
+	const unsigned char *data;
 	struct commit_graph *graph;
-	uint64_t next_chunk_offset;
 	uint32_t graph_signature;
 	unsigned char graph_version, hash_version;
+	struct chunkfile *cf = NULL;
 
 	if (!graph_map)
 		return NULL;
@@ -355,7 +374,7 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 	graph->data_len = graph_size;
 
 	if (graph_size < GRAPH_HEADER_SIZE +
-			 (graph->num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH +
+			 (graph->num_chunks + 1) * CHUNK_TOC_ENTRY_SIZE +
 			 GRAPH_FANOUT_SIZE + the_hash_algo->rawsz) {
 		error(_("commit-graph file is too small to hold %u chunks"),
 		      graph->num_chunks);
@@ -363,108 +382,28 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 		return NULL;
 	}
 
-	chunk_lookup = data + 8;
-	next_chunk_offset = get_be64(chunk_lookup + 4);
-	for (i = 0; i < graph->num_chunks; i++) {
-		uint32_t chunk_id;
-		uint64_t chunk_offset = next_chunk_offset;
-		int chunk_repeated = 0;
-
-		chunk_id = get_be32(chunk_lookup + 0);
-
-		chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
-		next_chunk_offset = get_be64(chunk_lookup + 4);
-
-		if (chunk_offset > graph_size - the_hash_algo->rawsz) {
-			error(_("commit-graph improper chunk offset %08x%08x"), (uint32_t)(chunk_offset >> 32),
-			      (uint32_t)chunk_offset);
-			goto free_and_return;
-		}
-
-		switch (chunk_id) {
-		case GRAPH_CHUNKID_OIDFANOUT:
-			if (graph->chunk_oid_fanout)
-				chunk_repeated = 1;
-			else
-				graph->chunk_oid_fanout = (uint32_t*)(data + chunk_offset);
-			break;
-
-		case GRAPH_CHUNKID_OIDLOOKUP:
-			if (graph->chunk_oid_lookup)
-				chunk_repeated = 1;
-			else {
-				graph->chunk_oid_lookup = data + chunk_offset;
-				graph->num_commits = (next_chunk_offset - chunk_offset)
-						     / graph->hash_len;
-			}
-			break;
-
-		case GRAPH_CHUNKID_DATA:
-			if (graph->chunk_commit_data)
-				chunk_repeated = 1;
-			else
-				graph->chunk_commit_data = data + chunk_offset;
-			break;
-
-		case GRAPH_CHUNKID_GENERATION_DATA:
-			if (graph->chunk_generation_data)
-				chunk_repeated = 1;
-			else
-				graph->chunk_generation_data = data + chunk_offset;
-			break;
-
-		case GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW:
-			if (graph->chunk_generation_data_overflow)
-				chunk_repeated = 1;
-			else
-				graph->chunk_generation_data_overflow = data + chunk_offset;
-			break;
-
-		case GRAPH_CHUNKID_EXTRAEDGES:
-			if (graph->chunk_extra_edges)
-				chunk_repeated = 1;
-			else
-				graph->chunk_extra_edges = data + chunk_offset;
-			break;
-
-		case GRAPH_CHUNKID_BASE:
-			if (graph->chunk_base_graphs)
-				chunk_repeated = 1;
-			else
-				graph->chunk_base_graphs = data + chunk_offset;
-			break;
-
-		case GRAPH_CHUNKID_BLOOMINDEXES:
-			if (graph->chunk_bloom_indexes)
-				chunk_repeated = 1;
-			else if (r->settings.commit_graph_read_changed_paths)
-				graph->chunk_bloom_indexes = data + chunk_offset;
-			break;
+	cf = init_chunkfile(NULL);
 
-		case GRAPH_CHUNKID_BLOOMDATA:
-			if (graph->chunk_bloom_data)
-				chunk_repeated = 1;
-			else if (r->settings.commit_graph_read_changed_paths) {
-				uint32_t hash_version;
-				graph->chunk_bloom_data = data + chunk_offset;
-				hash_version = get_be32(data + chunk_offset);
+	if (read_table_of_contents(cf, graph->data, graph_size,
+				   GRAPH_HEADER_SIZE, graph->num_chunks))
+		goto free_and_return;
 
-				if (hash_version != 1)
-					break;
+	pair_chunk(cf, GRAPH_CHUNKID_OIDFANOUT,
+		   (const unsigned char **)&graph->chunk_oid_fanout);
+	read_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, graph_read_oid_lookup, graph);
+	pair_chunk(cf, GRAPH_CHUNKID_DATA, &graph->chunk_commit_data);
+	pair_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES, &graph->chunk_extra_edges);
+	pair_chunk(cf, GRAPH_CHUNKID_BASE, &graph->chunk_base_graphs);
+	pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
+		   &graph->chunk_generation_data);
+	pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
+		   &graph->chunk_generation_data_overflow);
 
-				graph->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
-				graph->bloom_filter_settings->hash_version = hash_version;
-				graph->bloom_filter_settings->num_hashes = get_be32(data + chunk_offset + 4);
-				graph->bloom_filter_settings->bits_per_entry = get_be32(data + chunk_offset + 8);
-				graph->bloom_filter_settings->max_changed_paths = DEFAULT_BLOOM_MAX_CHANGES;
-			}
-			break;
-		}
-
-		if (chunk_repeated) {
-			error(_("commit-graph chunk id %08x appears multiple times"), chunk_id);
-			goto free_and_return;
-		}
+	if (r->settings.commit_graph_read_changed_paths) {
+		pair_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
+			   &graph->chunk_bloom_indexes);
+		read_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,
+			   graph_read_bloom_data, graph);
 	}
 
 	if (graph->chunk_bloom_indexes && graph->chunk_bloom_data) {
@@ -481,9 +420,11 @@ struct commit_graph *parse_commit_graph(struct repository *r,
 	if (verify_commit_graph_lite(graph))
 		goto free_and_return;
 
+	free_chunkfile(cf);
 	return graph;
 
 free_and_return:
+	free_chunkfile(cf);
 	free(graph->bloom_filter_settings);
 	free(graph);
 	return NULL;
@@ -1059,8 +1000,9 @@ struct write_commit_graph_context {
 };
 
 static int write_graph_chunk_fanout(struct hashfile *f,
-				    struct write_commit_graph_context *ctx)
+				    void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	int i, count = 0;
 	struct commit **list = ctx->commits.list;
 
@@ -1085,8 +1027,9 @@ static int write_graph_chunk_fanout(struct hashfile *f,
 }
 
 static int write_graph_chunk_oids(struct hashfile *f,
-				  struct write_commit_graph_context *ctx)
+				  void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	struct commit **list = ctx->commits.list;
 	int count;
 	for (count = 0; count < ctx->commits.nr; count++, list++) {
@@ -1104,8 +1047,9 @@ static const struct object_id *commit_to_oid(size_t index, const void *table)
 }
 
 static int write_graph_chunk_data(struct hashfile *f,
-				  struct write_commit_graph_context *ctx)
+				  void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	struct commit **list = ctx->commits.list;
 	struct commit **last = ctx->commits.list + ctx->commits.nr;
 	uint32_t num_extra_edges = 0;
@@ -1206,8 +1150,9 @@ static int write_graph_chunk_data(struct hashfile *f,
 }
 
 static int write_graph_chunk_generation_data(struct hashfile *f,
-					      struct write_commit_graph_context *ctx)
+					     void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	int i, num_generation_data_overflows = 0;
 
 	for (i = 0; i < ctx->commits.nr; i++) {
@@ -1229,8 +1174,9 @@ static int write_graph_chunk_generation_data(struct hashfile *f,
 }
 
 static int write_graph_chunk_generation_data_overflow(struct hashfile *f,
-						       struct write_commit_graph_context *ctx)
+						      void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	int i;
 	for (i = 0; i < ctx->commits.nr; i++) {
 		struct commit *c = ctx->commits.list[i];
@@ -1247,8 +1193,9 @@ static int write_graph_chunk_generation_data_overflow(struct hashfile *f,
 }
 
 static int write_graph_chunk_extra_edges(struct hashfile *f,
-					 struct write_commit_graph_context *ctx)
+					 void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	struct commit **list = ctx->commits.list;
 	struct commit **last = ctx->commits.list + ctx->commits.nr;
 	struct commit_list *parent;
@@ -1301,8 +1248,9 @@ static int write_graph_chunk_extra_edges(struct hashfile *f,
 }
 
 static int write_graph_chunk_bloom_indexes(struct hashfile *f,
-					   struct write_commit_graph_context *ctx)
+					   void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	struct commit **list = ctx->commits.list;
 	struct commit **last = ctx->commits.list + ctx->commits.nr;
 	uint32_t cur_pos = 0;
@@ -1336,8 +1284,9 @@ static void trace2_bloom_filter_settings(struct write_commit_graph_context *ctx)
 }
 
 static int write_graph_chunk_bloom_data(struct hashfile *f,
-					struct write_commit_graph_context *ctx)
+					void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	struct commit **list = ctx->commits.list;
 	struct commit **last = ctx->commits.list + ctx->commits.nr;
 
@@ -1813,8 +1762,9 @@ static int write_graph_chunk_base_1(struct hashfile *f,
 }
 
 static int write_graph_chunk_base(struct hashfile *f,
-				  struct write_commit_graph_context *ctx)
+				    void *data)
 {
+	struct write_commit_graph_context *ctx = data;
 	int num = write_graph_chunk_base_1(f, ctx->new_base_graph);
 
 	if (num != ctx->num_commit_graphs_after - 1) {
@@ -1825,27 +1775,16 @@ static int write_graph_chunk_base(struct hashfile *f,
 	return 0;
 }
 
-typedef int (*chunk_write_fn)(struct hashfile *f,
-			      struct write_commit_graph_context *ctx);
-
-struct chunk_info {
-	uint32_t id;
-	uint64_t size;
-	chunk_write_fn write_fn;
-};
-
 static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 {
 	uint32_t i;
 	int fd;
 	struct hashfile *f;
 	struct lock_file lk = LOCK_INIT;
-	struct chunk_info chunks[MAX_NUM_CHUNKS + 1];
 	const unsigned hashsz = the_hash_algo->rawsz;
 	struct strbuf progress_title = STRBUF_INIT;
-	int num_chunks = 3;
-	uint64_t chunk_offset;
 	struct object_id file_hash;
+	struct chunkfile *cf;
 
 	if (ctx->split) {
 		struct strbuf tmp_file = STRBUF_INIT;
@@ -1891,98 +1830,62 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		f = hashfd(fd, get_lock_file_path(&lk));
 	}
 
-	chunks[0].id = GRAPH_CHUNKID_OIDFANOUT;
-	chunks[0].size = GRAPH_FANOUT_SIZE;
-	chunks[0].write_fn = write_graph_chunk_fanout;
-	chunks[1].id = GRAPH_CHUNKID_OIDLOOKUP;
-	chunks[1].size = hashsz * ctx->commits.nr;
-	chunks[1].write_fn = write_graph_chunk_oids;
-	chunks[2].id = GRAPH_CHUNKID_DATA;
-	chunks[2].size = (hashsz + 16) * ctx->commits.nr;
-	chunks[2].write_fn = write_graph_chunk_data;
+	cf = init_chunkfile(f);
+
+	add_chunk(cf, GRAPH_CHUNKID_OIDFANOUT, GRAPH_FANOUT_SIZE,
+		  write_graph_chunk_fanout);
+	add_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, hashsz * ctx->commits.nr,
+		  write_graph_chunk_oids);
+	add_chunk(cf, GRAPH_CHUNKID_DATA, (hashsz + 16) * ctx->commits.nr,
+		  write_graph_chunk_data);
 
 	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_NO_GDAT, 0))
 		ctx->write_generation_data = 0;
-	if (ctx->write_generation_data) {
-		chunks[num_chunks].id = GRAPH_CHUNKID_GENERATION_DATA;
-		chunks[num_chunks].size = sizeof(uint32_t) * ctx->commits.nr;
-		chunks[num_chunks].write_fn = write_graph_chunk_generation_data;
-		num_chunks++;
-	}
-	if (ctx->num_generation_data_overflows) {
-		chunks[num_chunks].id = GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW;
-		chunks[num_chunks].size = sizeof(timestamp_t) * ctx->num_generation_data_overflows;
-		chunks[num_chunks].write_fn = write_graph_chunk_generation_data_overflow;
-		num_chunks++;
-	}
-	if (ctx->num_extra_edges) {
-		chunks[num_chunks].id = GRAPH_CHUNKID_EXTRAEDGES;
-		chunks[num_chunks].size = 4 * ctx->num_extra_edges;
-		chunks[num_chunks].write_fn = write_graph_chunk_extra_edges;
-		num_chunks++;
-	}
+	if (ctx->write_generation_data)
+		add_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
+			  sizeof(uint32_t) * ctx->commits.nr,
+			  write_graph_chunk_generation_data);
+	if (ctx->num_generation_data_overflows)
+		add_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
+			  sizeof(timestamp_t) * ctx->num_generation_data_overflows,
+			  write_graph_chunk_generation_data_overflow);
+	if (ctx->num_extra_edges)
+		add_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES,
+			  4 * ctx->num_extra_edges,
+			  write_graph_chunk_extra_edges);
 	if (ctx->changed_paths) {
-		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMINDEXES;
-		chunks[num_chunks].size = sizeof(uint32_t) * ctx->commits.nr;
-		chunks[num_chunks].write_fn = write_graph_chunk_bloom_indexes;
-		num_chunks++;
-		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMDATA;
-		chunks[num_chunks].size = sizeof(uint32_t) * 3
-					  + ctx->total_bloom_filter_data_size;
-		chunks[num_chunks].write_fn = write_graph_chunk_bloom_data;
-		num_chunks++;
-	}
-	if (ctx->num_commit_graphs_after > 1) {
-		chunks[num_chunks].id = GRAPH_CHUNKID_BASE;
-		chunks[num_chunks].size = hashsz * (ctx->num_commit_graphs_after - 1);
-		chunks[num_chunks].write_fn = write_graph_chunk_base;
-		num_chunks++;
-	}
-
-	chunks[num_chunks].id = 0;
-	chunks[num_chunks].size = 0;
+		add_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
+			  sizeof(uint32_t) * ctx->commits.nr,
+			  write_graph_chunk_bloom_indexes);
+		add_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,
+			  sizeof(uint32_t) * 3
+				+ ctx->total_bloom_filter_data_size,
+			  write_graph_chunk_bloom_data);
+	}
+	if (ctx->num_commit_graphs_after > 1)
+		add_chunk(cf, GRAPH_CHUNKID_BASE,
+			  hashsz * (ctx->num_commit_graphs_after - 1),
+			  write_graph_chunk_base);
 
 	hashwrite_be32(f, GRAPH_SIGNATURE);
 
 	hashwrite_u8(f, GRAPH_VERSION);
 	hashwrite_u8(f, oid_version());
-	hashwrite_u8(f, num_chunks);
+	hashwrite_u8(f, get_num_chunks(cf));
 	hashwrite_u8(f, ctx->num_commit_graphs_after - 1);
 
-	chunk_offset = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
-	for (i = 0; i <= num_chunks; i++) {
-		uint32_t chunk_write[3];
-
-		chunk_write[0] = htonl(chunks[i].id);
-		chunk_write[1] = htonl(chunk_offset >> 32);
-		chunk_write[2] = htonl(chunk_offset & 0xffffffff);
-		hashwrite(f, chunk_write, 12);
-
-		chunk_offset += chunks[i].size;
-	}
-
 	if (ctx->report_progress) {
 		strbuf_addf(&progress_title,
 			    Q_("Writing out commit graph in %d pass",
 			       "Writing out commit graph in %d passes",
-			       num_chunks),
-			    num_chunks);
+			       get_num_chunks(cf)),
+			    get_num_chunks(cf));
 		ctx->progress = start_delayed_progress(
 			progress_title.buf,
-			num_chunks * ctx->commits.nr);
+			get_num_chunks(cf) * ctx->commits.nr);
 	}
 
-	for (i = 0; i < num_chunks; i++) {
-		uint64_t start_offset = f->total + f->offset;
-
-		if (chunks[i].write_fn(f, ctx))
-			return -1;
-
-		if (f->total + f->offset != start_offset + chunks[i].size)
-			BUG("expected to write %"PRId64" bytes to chunk %"PRIx32", but wrote %"PRId64" instead",
-			    chunks[i].size, chunks[i].id,
-			    f->total + f->offset - start_offset);
-	}
+	write_chunkfile(cf, ctx);
 
 	stop_progress(&ctx->progress);
 	strbuf_release(&progress_title);
@@ -1999,6 +1902,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 
 	close_commit_graph(ctx->r->objects);
 	finalize_hashfile(f, file_hash.hash, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
+	free_chunkfile(cf);
 
 	if (ctx->split) {
 		FILE *chainf = fdopen_lock_file(&lk, "w");
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 8fe6c9384b..41558185ae 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -367,6 +367,144 @@ static int find_exact_renames(struct diff_options *options)
 	return renames;
 }
 
+static const char *get_basename(const char *filename)
+{
+	/*
+	 * gitbasename() has to worry about special drives, multiple
+	 * directory separator characters, trailing slashes, NULL or
+	 * empty strings, etc.  We only work on filenames as stored in
+	 * git, and thus get to ignore all those complications.
+	 */
+	const char *base = strrchr(filename, '/');
+	return base ? base + 1 : filename;
+}
+
+static int find_basename_matches(struct diff_options *options,
+				 int minimum_score)
+{
+	/*
+	 * When I checked in early 2020, over 76% of file renames in linux
+	 * just moved files to a different directory but kept the same
+	 * basename.  gcc did that with over 64% of renames, gecko did it
+	 * with over 79%, and WebKit did it with over 89%.
+	 *
+	 * Therefore we can bypass the normal exhaustive NxM matrix
+	 * comparison of similarities between all potential rename sources
+	 * and destinations by instead using file basename as a hint (i.e.
+	 * the portion of the filename after the last '/'), checking for
+	 * similarity between files with the same basename, and if we find
+	 * a pair that are sufficiently similar, record the rename pair and
+	 * exclude those two from the NxM matrix.
+	 *
+	 * This *might* cause us to find a less than optimal pairing (if
+	 * there is another file that we are even more similar to but has a
+	 * different basename).  Given the huge performance advantage
+	 * basename matching provides, and given the frequency with which
+	 * people use the same basename in real world projects, that's a
+	 * trade-off we are willing to accept when doing just rename
+	 * detection.
+	 *
+	 * If someone wants copy detection that implies they are willing to
+	 * spend more cycles to find similarities between files, so it may
+	 * be less likely that this heuristic is wanted.  If someone is
+	 * doing break detection, that means they do not want filename
+	 * similarity to imply any form of content similiarity, and thus
+	 * this heuristic would definitely be incompatible.
+	 */
+
+	int i, renames = 0;
+	struct strintmap sources;
+	struct strintmap dests;
+	struct hashmap_iter iter;
+	struct strmap_entry *entry;
+
+	/*
+	 * The prefeteching stuff wants to know if it can skip prefetching
+	 * blobs that are unmodified...and will then do a little extra work
+	 * to verify that the oids are indeed different before prefetching.
+	 * Unmodified blobs are only relevant when doing copy detection;
+	 * when limiting to rename detection, diffcore_rename[_extended]()
+	 * will never be called with unmodified source paths fed to us, so
+	 * the extra work necessary to check if rename_src entries are
+	 * unmodified would be a small waste.
+	 */
+	int skip_unmodified = 0;
+
+	/*
+	 * Create maps of basename -> fullname(s) for remaining sources and
+	 * dests.
+	 */
+	strintmap_init_with_options(&sources, -1, NULL, 0);
+	strintmap_init_with_options(&dests, -1, NULL, 0);
+	for (i = 0; i < rename_src_nr; ++i) {
+		char *filename = rename_src[i].p->one->path;
+		const char *base;
+
+		/* exact renames removed in remove_unneeded_paths_from_src() */
+		assert(!rename_src[i].p->one->rename_used);
+
+		/* Record index within rename_src (i) if basename is unique */
+		base = get_basename(filename);
+		if (strintmap_contains(&sources, base))
+			strintmap_set(&sources, base, -1);
+		else
+			strintmap_set(&sources, base, i);
+	}
+	for (i = 0; i < rename_dst_nr; ++i) {
+		char *filename = rename_dst[i].p->two->path;
+		const char *base;
+
+		if (rename_dst[i].is_rename)
+			continue; /* involved in exact match already. */
+
+		/* Record index within rename_dst (i) if basename is unique */
+		base = get_basename(filename);
+		if (strintmap_contains(&dests, base))
+			strintmap_set(&dests, base, -1);
+		else
+			strintmap_set(&dests, base, i);
+	}
+
+	/* Now look for basename matchups and do similarity estimation */
+	strintmap_for_each_entry(&sources, &iter, entry) {
+		const char *base = entry->key;
+		intptr_t src_index = (intptr_t)entry->value;
+		intptr_t dst_index;
+		if (src_index == -1)
+			continue;
+
+		if (0 <= (dst_index = strintmap_get(&dests, base))) {
+			struct diff_filespec *one, *two;
+			int score;
+
+			/* Estimate the similarity */
+			one = rename_src[src_index].p->one;
+			two = rename_dst[dst_index].p->two;
+			score = estimate_similarity(options->repo, one, two,
+						    minimum_score, skip_unmodified);
+
+			/* If sufficiently similar, record as rename pair */
+			if (score < minimum_score)
+				continue;
+			record_rename_pair(dst_index, src_index, score);
+			renames++;
+
+			/*
+			 * Found a rename so don't need text anymore; if we
+			 * didn't find a rename, the filespec_blob would get
+			 * re-used when doing the matrix of comparisons.
+			 */
+			diff_free_filespec_blob(one);
+			diff_free_filespec_blob(two);
+		}
+	}
+
+	strintmap_clear(&sources);
+	strintmap_clear(&dests);
+
+	return renames;
+}
+
 #define NUM_CANDIDATE_PER_DST 4
 static void record_if_better(struct diff_score m[], struct diff_score *o)
 {
@@ -454,6 +592,54 @@ static int find_renames(struct diff_score *mx, int dst_cnt, int minimum_score, i
 	return count;
 }
 
+static void remove_unneeded_paths_from_src(int detecting_copies)
+{
+	int i, new_num_src;
+
+	if (detecting_copies)
+		return; /* nothing to remove */
+	if (break_idx)
+		return; /* culling incompatible with break detection */
+
+	/*
+	 * Note on reasons why we cull unneeded sources but not destinations:
+	 *   1) Pairings are stored in rename_dst (not rename_src), which we
+	 *      need to keep around.  So, we just can't cull rename_dst even
+	 *      if we wanted to.  But doing so wouldn't help because...
+	 *
+	 *   2) There is a matrix pairwise comparison that follows the
+	 *      "Performing inexact rename detection" progress message.
+	 *      Iterating over the destinations is done in the outer loop,
+	 *      hence we only iterate over each of those once and we can
+	 *      easily skip the outer loop early if the destination isn't
+	 *      relevant.  That's only one check per destination path to
+	 *      skip.
+	 *
+	 *      By contrast, the sources are iterated in the inner loop; if
+	 *      we check whether a source can be skipped, then we'll be
+	 *      checking it N separate times, once for each destination.
+	 *      We don't want to have to iterate over known-not-needed
+	 *      sources N times each, so avoid that by removing the sources
+	 *      from rename_src here.
+	 */
+	for (i = 0, new_num_src = 0; i < rename_src_nr; i++) {
+		/*
+		 * renames are stored in rename_dst, so if a rename has
+		 * already been detected using this source, we can just
+		 * remove the source knowing rename_dst has its info.
+		 */
+		if (rename_src[i].p->one->rename_used)
+			continue;
+
+		if (new_num_src < i)
+			memcpy(&rename_src[new_num_src], &rename_src[i],
+			       sizeof(struct diff_rename_src));
+		new_num_src++;
+	}
+
+	rename_src_nr = new_num_src;
+}
+
 void diffcore_rename(struct diff_options *options)
 {
 	int detect_rename = options->detect_rename;
@@ -463,9 +649,11 @@ void diffcore_rename(struct diff_options *options)
 	struct diff_score *mx;
 	int i, j, rename_count, skip_unmodified = 0;
 	int num_destinations, dst_cnt;
+	int num_sources, want_copies;
 	struct progress *progress = NULL;
 
 	trace2_region_enter("diff", "setup", options->repo);
+	want_copies = (detect_rename == DIFF_DETECT_COPY);
 	if (!minimum_score)
 		minimum_score = DEFAULT_RENAME_SCORE;
 
@@ -502,7 +690,7 @@ void diffcore_rename(struct diff_options *options)
 				p->one->rename_used++;
 			register_rename_src(p);
 		}
-		else if (detect_rename == DIFF_DETECT_COPY) {
+		else if (want_copies) {
 			/*
 			 * Increment the "rename_used" score by
 			 * one, to indicate ourselves as a user.
@@ -527,17 +715,60 @@ void diffcore_rename(struct diff_options *options)
 	if (minimum_score == MAX_SCORE)
 		goto cleanup;
 
-	/*
-	 * Calculate how many renames are left (but all the source
-	 * files still remain as options for rename/copies!)
-	 */
+	num_sources = rename_src_nr;
+
+	if (want_copies || break_idx) {
+		/*
+		 * Cull sources:
+		 *   - remove ones corresponding to exact renames
+		 */
+		trace2_region_enter("diff", "cull after exact", options->repo);
+		remove_unneeded_paths_from_src(want_copies);
+		trace2_region_leave("diff", "cull after exact", options->repo);
+	} else {
+		/* Determine minimum score to match basenames */
+		double factor = 0.5;
+		char *basename_factor = getenv("GIT_BASENAME_FACTOR");
+		int min_basename_score;
+
+		if (basename_factor)
+			factor = strtol(basename_factor, NULL, 10)/100.0;
+		assert(factor >= 0.0 && factor <= 1.0);
+		min_basename_score = minimum_score +
+			(int)(factor * (MAX_SCORE - minimum_score));
+
+		/*
+		 * Cull sources:
+		 *   - remove ones involved in renames (found via exact match)
+		 */
+		trace2_region_enter("diff", "cull after exact", options->repo);
+		remove_unneeded_paths_from_src(want_copies);
+		trace2_region_leave("diff", "cull after exact", options->repo);
+
+		/* Utilize file basenames to quickly find renames. */
+		trace2_region_enter("diff", "basename matches", options->repo);
+		rename_count += find_basename_matches(options,
+						      min_basename_score);
+		trace2_region_leave("diff", "basename matches", options->repo);
+
+		/*
+		 * Cull sources, again:
+		 *   - remove ones involved in renames (found via basenames)
+		 */
+		trace2_region_enter("diff", "cull basename", options->repo);
+		remove_unneeded_paths_from_src(want_copies);
+		trace2_region_leave("diff", "cull basename", options->repo);
+	}
+
+	/* Calculate how many rename destinations are left */
 	num_destinations = (rename_dst_nr - rename_count);
+	num_sources = rename_src_nr; /* rename_src_nr reflects lower number */
 
 	/* All done? */
-	if (!num_destinations)
+	if (!num_destinations || !num_sources)
 		goto cleanup;
 
-	switch (too_many_rename_candidates(num_destinations, rename_src_nr,
+	switch (too_many_rename_candidates(num_destinations, num_sources,
 					   options)) {
 	case 1:
 		goto cleanup;
@@ -553,7 +784,7 @@ void diffcore_rename(struct diff_options *options)
 	if (options->show_rename_progress) {
 		progress = start_delayed_progress(
 				_("Performing inexact rename detection"),
-				(uint64_t)num_destinations * (uint64_t)rename_src_nr);
+				(uint64_t)num_destinations * (uint64_t)num_sources);
 	}
 
 	mx = xcalloc(st_mult(NUM_CANDIDATE_PER_DST, num_destinations),
@@ -563,7 +794,7 @@ void diffcore_rename(struct diff_options *options)
 		struct diff_score *m;
 
 		if (rename_dst[i].is_rename)
-			continue; /* dealt with exact match already. */
+			continue; /* exact or basename match already handled */
 
 		m = &mx[dst_cnt * NUM_CANDIDATE_PER_DST];
 		for (j = 0; j < NUM_CANDIDATE_PER_DST; j++)
@@ -573,6 +804,8 @@ void diffcore_rename(struct diff_options *options)
 			struct diff_filespec *one = rename_src[j].p->one;
 			struct diff_score this_src;
 
+			assert(!one->rename_used || want_copies || break_idx);
+
 			if (skip_unmodified &&
 			    diff_unmodified_pair(rename_src[j].p))
 				continue;
@@ -594,7 +827,7 @@ void diffcore_rename(struct diff_options *options)
 		}
 		dst_cnt++;
 		display_progress(progress,
-				 (uint64_t)dst_cnt * (uint64_t)rename_src_nr);
+				 (uint64_t)dst_cnt * (uint64_t)num_sources);
 	}
 	stop_progress(&progress);
 
@@ -602,7 +835,7 @@ void diffcore_rename(struct diff_options *options)
 	STABLE_QSORT(mx, dst_cnt * NUM_CANDIDATE_PER_DST, score_compare);
 
 	rename_count += find_renames(mx, dst_cnt, minimum_score, 0);
-	if (detect_rename == DIFF_DETECT_COPY)
+	if (want_copies)
 		rename_count += find_renames(mx, dst_cnt, minimum_score, 1);
 	free(mx);
 	trace2_region_leave("diff", "inexact renames", options->repo);
diff --git a/dir.c b/dir.c
index d153a63bbd..fd8aa7c40f 100644
--- a/dir.c
+++ b/dir.c
@@ -2730,11 +2730,8 @@ static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *d
 		return NULL;
 	}
 
-	if (!dir->untracked->root) {
-		const int len = sizeof(*dir->untracked->root);
-		dir->untracked->root = xmalloc(len);
-		memset(dir->untracked->root, 0, len);
-	}
+	if (!dir->untracked->root)
+		FLEX_ALLOC_STR(dir->untracked->root, name, "");
 
 	/* Validate $GIT_DIR/info/exclude and core.excludesfile */
 	root = dir->untracked->root;
diff --git a/fetch-pack.c b/fetch-pack.c
index 1eaedcb5dc..0cb59acc48 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -790,14 +790,36 @@ static void create_promisor_file(const char *keep_name,
 	strbuf_release(&promisor_name);
 }
 
+static void parse_gitmodules_oids(int fd, struct oidset *gitmodules_oids)
+{
+	int len = the_hash_algo->hexsz + 1; /* hash + NL */
+
+	do {
+		char hex_hash[GIT_MAX_HEXSZ + 1];
+		int read_len = read_in_full(fd, hex_hash, len);
+		struct object_id oid;
+		const char *end;
+
+		if (!read_len)
+			return;
+		if (read_len != len)
+			die("invalid length read %d", read_len);
+		if (parse_oid_hex(hex_hash, &oid, &end) || *end != '\n')
+			die("invalid hash");
+		oidset_insert(gitmodules_oids, &oid);
+	} while (1);
+}
+
 /*
- * Pass 1 as "only_packfile" if the pack received is the only pack in this
- * fetch request (that is, if there were no packfile URIs provided).
+ * If packfile URIs were provided, pass a non-NULL pointer to index_pack_args.
+ * The strings to pass as the --index-pack-arg arguments to http-fetch will be
+ * stored there. (It must be freed by the caller.)
  */
 static int get_pack(struct fetch_pack_args *args,
 		    int xd[2], struct string_list *pack_lockfiles,
-		    int only_packfile,
-		    struct ref **sought, int nr_sought)
+		    struct strvec *index_pack_args,
+		    struct ref **sought, int nr_sought,
+		    struct oidset *gitmodules_oids)
 {
 	struct async demux;
 	int do_keep = args->keep_pack;
@@ -805,6 +827,7 @@ static int get_pack(struct fetch_pack_args *args,
 	struct pack_header header;
 	int pass_header = 0;
 	struct child_process cmd = CHILD_PROCESS_INIT;
+	int fsck_objects = 0;
 	int ret;
 
 	memset(&demux, 0, sizeof(demux));
@@ -839,8 +862,15 @@ static int get_pack(struct fetch_pack_args *args,
 		strvec_push(&cmd.args, alternate_shallow_file);
 	}
 
-	if (do_keep || args->from_promisor) {
-		if (pack_lockfiles)
+	if (fetch_fsck_objects >= 0
+	    ? fetch_fsck_objects
+	    : transfer_fsck_objects >= 0
+	    ? transfer_fsck_objects
+	    : 0)
+		fsck_objects = 1;
+
+	if (do_keep || args->from_promisor || index_pack_args || fsck_objects) {
+		if (pack_lockfiles || fsck_objects)
 			cmd.out = -1;
 		cmd_name = "index-pack";
 		strvec_push(&cmd.args, cmd_name);
@@ -857,7 +887,7 @@ static int get_pack(struct fetch_pack_args *args,
 				     "--keep=fetch-pack %"PRIuMAX " on %s",
 				     (uintmax_t)getpid(), hostname);
 		}
-		if (only_packfile && args->check_self_contained_and_connected)
+		if (!index_pack_args && args->check_self_contained_and_connected)
 			strvec_push(&cmd.args, "--check-self-contained-and-connected");
 		else
 			/*
@@ -890,12 +920,8 @@ static int get_pack(struct fetch_pack_args *args,
 		strvec_pushf(&cmd.args, "--pack_header=%"PRIu32",%"PRIu32,
 			     ntohl(header.hdr_version),
 				 ntohl(header.hdr_entries));
-	if (fetch_fsck_objects >= 0
-	    ? fetch_fsck_objects
-	    : transfer_fsck_objects >= 0
-	    ? transfer_fsck_objects
-	    : 0) {
-		if (args->from_promisor || !only_packfile)
+	if (fsck_objects) {
+		if (args->from_promisor || index_pack_args)
 			/*
 			 * We cannot use --strict in index-pack because it
 			 * checks both broken objects and links, but we only
@@ -907,14 +933,26 @@ static int get_pack(struct fetch_pack_args *args,
 				     fsck_msg_types.buf);
 	}
 
+	if (index_pack_args) {
+		int i;
+
+		for (i = 0; i < cmd.args.nr; i++)
+			strvec_push(index_pack_args, cmd.args.v[i]);
+	}
+
 	cmd.in = demux.out;
 	cmd.git_cmd = 1;
 	if (start_command(&cmd))
 		die(_("fetch-pack: unable to fork off %s"), cmd_name);
-	if (do_keep && pack_lockfiles) {
-		char *pack_lockfile = index_pack_lockfile(cmd.out);
+	if (do_keep && (pack_lockfiles || fsck_objects)) {
+		int is_well_formed;
+		char *pack_lockfile = index_pack_lockfile(cmd.out, &is_well_formed);
+
+		if (!is_well_formed)
+			die(_("fetch-pack: invalid index-pack output"));
 		if (pack_lockfile)
 			string_list_append_nodup(pack_lockfiles, pack_lockfile);
+		parse_gitmodules_oids(cmd.out, gitmodules_oids);
 		close(cmd.out);
 	}
 
@@ -949,6 +987,22 @@ static int cmp_ref_by_name(const void *a_, const void *b_)
 	return strcmp(a->name, b->name);
 }
 
+static void fsck_gitmodules_oids(struct oidset *gitmodules_oids)
+{
+	struct oidset_iter iter;
+	const struct object_id *oid;
+	struct fsck_options fo = FSCK_OPTIONS_STRICT;
+
+	if (!oidset_size(gitmodules_oids))
+		return;
+
+	oidset_iter_init(gitmodules_oids, &iter);
+	while ((oid = oidset_iter_next(&iter)))
+		register_found_gitmodules(oid);
+	if (fsck_finish(&fo))
+		die("fsck failed");
+}
+
 static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 				 int fd[2],
 				 const struct ref *orig_ref,
@@ -963,6 +1017,7 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 	int agent_len;
 	struct fetch_negotiator negotiator_alloc;
 	struct fetch_negotiator *negotiator;
+	struct oidset gitmodules_oids = OIDSET_INIT;
 
 	negotiator = &negotiator_alloc;
 	fetch_negotiator_init(r, negotiator);
@@ -1078,8 +1133,10 @@ static struct ref *do_fetch_pack(struct fetch_pack_args *args,
 		alternate_shallow_file = setup_temporary_shallow(si->shallow);
 	else
 		alternate_shallow_file = NULL;
-	if (get_pack(args, fd, pack_lockfiles, 1, sought, nr_sought))
+	if (get_pack(args, fd, pack_lockfiles, NULL, sought, nr_sought,
+		     &gitmodules_oids))
 		die(_("git fetch-pack: fetch failed."));
+	fsck_gitmodules_oids(&gitmodules_oids);
 
  all_done:
 	if (negotiator)
@@ -1529,6 +1586,8 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	int seen_ack = 0;
 	struct string_list packfile_uris = STRING_LIST_INIT_DUP;
 	int i;
+	struct strvec index_pack_args = STRVEC_INIT;
+	struct oidset gitmodules_oids = OIDSET_INIT;
 
 	negotiator = &negotiator_alloc;
 	fetch_negotiator_init(r, negotiator);
@@ -1618,7 +1677,8 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				receive_packfile_uris(&reader, &packfile_uris);
 			process_section_header(&reader, "packfile", 0);
 			if (get_pack(args, fd, pack_lockfiles,
-				     !packfile_uris.nr, sought, nr_sought))
+				     packfile_uris.nr ? &index_pack_args : NULL,
+				     sought, nr_sought, &gitmodules_oids))
 				die(_("git fetch-pack: fetch failed."));
 			do_check_stateless_delimiter(args, &reader);
 
@@ -1630,6 +1690,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 	}
 
 	for (i = 0; i < packfile_uris.nr; i++) {
+		int j;
 		struct child_process cmd = CHILD_PROCESS_INIT;
 		char packname[GIT_MAX_HEXSZ + 1];
 		const char *uri = packfile_uris.items[i].string +
@@ -1639,6 +1700,9 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 		strvec_pushf(&cmd.args, "--packfile=%.*s",
 			     (int) the_hash_algo->hexsz,
 			     packfile_uris.items[i].string);
+		for (j = 0; j < index_pack_args.nr; j++)
+			strvec_pushf(&cmd.args, "--index-pack-arg=%s",
+				     index_pack_args.v[j]);
 		strvec_push(&cmd.args, uri);
 		cmd.git_cmd = 1;
 		cmd.no_stdin = 1;
@@ -1657,6 +1721,8 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 
 		packname[the_hash_algo->hexsz] = '\0';
 
+		parse_gitmodules_oids(cmd.out, &gitmodules_oids);
+
 		close(cmd.out);
 
 		if (finish_command(&cmd))
@@ -1674,6 +1740,9 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 						 packname));
 	}
 	string_list_clear(&packfile_uris, 0);
+	strvec_clear(&index_pack_args);
+
+	fsck_gitmodules_oids(&gitmodules_oids);
 
 	if (negotiator)
 		negotiator->release(negotiator);
diff --git a/fsck.c b/fsck.c
index 71134fdefa..e3030f3b35 100644
--- a/fsck.c
+++ b/fsck.c
@@ -1276,6 +1276,11 @@ int fsck_error_function(struct fsck_options *o,
 	return 1;
 }
 
+void register_found_gitmodules(const struct object_id *oid)
+{
+	oidset_insert(&gitmodules_found, oid);
+}
+
 int fsck_finish(struct fsck_options *options)
 {
 	int ret = 0;
diff --git a/fsck.h b/fsck.h
index 423c467feb..733378f126 100644
--- a/fsck.h
+++ b/fsck.h
@@ -62,6 +62,8 @@ int fsck_walk(struct object *obj, void *data, struct fsck_options *options);
 int fsck_object(struct object *obj, void *data, unsigned long size,
 	struct fsck_options *options);
 
+void register_found_gitmodules(const struct object_id *oid);
+
 /*
  * fsck a tag, and pass info about it back to the caller. This is
  * exposed fsck_object() internals for git-mktag(1).
diff --git a/fsmonitor.c b/fsmonitor.c
index fe9e9d7baf..23f8a0c97e 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -90,7 +90,11 @@ int read_fsmonitor_extension(struct index_state *istate, const void *data,
 	if (!istate->split_index)
 		assert_index_minimum(istate, istate->fsmonitor_dirty->bit_size);
 
-	trace_printf_key(&trace_fsmonitor, "read fsmonitor extension successful");
+	trace2_data_string("index", NULL, "extension/fsmn/read/token",
+			   istate->fsmonitor_last_update);
+	trace_printf_key(&trace_fsmonitor,
+			 "read fsmonitor extension successful '%s'",
+			 istate->fsmonitor_last_update);
 	return 0;
 }
 
@@ -134,7 +138,11 @@ void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
 	put_be32(&ewah_size, sb->len - ewah_start);
 	memcpy(sb->buf + fixup, &ewah_size, sizeof(uint32_t));
 
-	trace_printf_key(&trace_fsmonitor, "write fsmonitor extension successful");
+	trace2_data_string("index", NULL, "extension/fsmn/write/token",
+			   istate->fsmonitor_last_update);
+	trace_printf_key(&trace_fsmonitor,
+			 "write fsmonitor extension successful '%s'",
+			 istate->fsmonitor_last_update);
 }
 
 /*
@@ -143,6 +151,7 @@ void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)
 static int query_fsmonitor(int version, const char *last_update, struct strbuf *query_result)
 {
 	struct child_process cp = CHILD_PROCESS_INIT;
+	int result;
 
 	if (!core_fsmonitor)
 		return -1;
@@ -153,16 +162,63 @@ static int query_fsmonitor(int version, const char *last_update, struct strbuf *
 	cp.use_shell = 1;
 	cp.dir = get_git_work_tree();
 
-	return capture_command(&cp, query_result, 1024);
+	trace2_region_enter("fsm_hook", "query", NULL);
+
+	result = capture_command(&cp, query_result, 1024);
+
+	if (result)
+		trace2_data_intmax("fsm_hook", NULL, "query/failed", result);
+	else {
+		trace2_data_intmax("fsm_hook", NULL, "query/response-length",
+				   query_result->len);
+
+		if (fsmonitor_is_trivial_response(query_result))
+			trace2_data_intmax("fsm_hook", NULL,
+					   "query/trivial-response", 1);
+	}
+
+	trace2_region_leave("fsm_hook", "query", NULL);
+
+	return result;
 }
 
-static void fsmonitor_refresh_callback(struct index_state *istate, const char *name)
+int fsmonitor_is_trivial_response(const struct strbuf *query_result)
 {
-	int pos = index_name_pos(istate, name, strlen(name));
+	static char trivial_response[3] = { '\0', '/', '\0' };
+	int is_trivial = !memcmp(trivial_response,
+				 &query_result->buf[query_result->len - 3], 3);
+
+	return is_trivial;
+}
+
+static void fsmonitor_refresh_callback(struct index_state *istate, char *name)
+{
+	int i, len = strlen(name);
+	if (name[len - 1] == '/') {
+
+		/*
+		 * TODO We should binary search to find the first path with
+		 * TODO this directory prefix.  Then linearly update entries
+		 * TODO while the prefix matches.  Taking care to search without
+		 * TODO the trailing slash -- because '/' sorts after a few
+		 * TODO interesting special chars, like '.' and ' '.
+		 */
+
+		/* Mark all entries for the folder invalid */
+		for (i = 0; i < istate->cache_nr; i++) {
+			if (istate->cache[i]->ce_flags & CE_FSMONITOR_VALID &&
+			    starts_with(istate->cache[i]->name, name))
+				istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;
+		}
+		/* Need to remove the / from the path for the untracked cache */
+		name[len - 1] = '\0';
+	} else {
+		int pos = index_name_pos(istate, name, strlen(name));
 
-	if (pos >= 0) {
-		struct cache_entry *ce = istate->cache[pos];
-		ce->ce_flags &= ~CE_FSMONITOR_VALID;
+		if (pos >= 0) {
+			struct cache_entry *ce = istate->cache[pos];
+			ce->ce_flags &= ~CE_FSMONITOR_VALID;
+		}
 	}
 
 	/*
@@ -288,16 +344,45 @@ void refresh_fsmonitor(struct index_state *istate)
 	istate->fsmonitor_last_update = strbuf_detach(&last_update_token, NULL);
 }
 
+/*
+ * The caller wants to turn on FSMonitor.  And when the caller writes
+ * the index to disk, a FSMonitor extension should be included.  This
+ * requires that `istate->fsmonitor_last_update` not be NULL.  But we
+ * have not actually talked to a FSMonitor process yet, so we don't
+ * have an initial value for this field.
+ *
+ * For a protocol V1 FSMonitor process, this field is a formatted
+ * "nanoseconds since epoch" field.  However, for a protocol V2
+ * FSMonitor process, this field is an opaque token.
+ *
+ * Historically, `add_fsmonitor()` has initialized this field to the
+ * current time for protocol V1 processes.  There are lots of race
+ * conditions here, but that code has shipped...
+ *
+ * The only true solution is to use a V2 FSMonitor and get a current
+ * or default token value (that it understands), but we cannot do that
+ * until we have actually talked to an instance of the FSMonitor process
+ * (but the protocol requires that we send a token first...).
+ *
+ * For simplicity, just initialize like we have a V1 process and require
+ * that V2 processes adapt.
+ */
+static void initialize_fsmonitor_last_update(struct index_state *istate)
+{
+	struct strbuf last_update = STRBUF_INIT;
+
+	strbuf_addf(&last_update, "%"PRIu64"", getnanotime());
+	istate->fsmonitor_last_update = strbuf_detach(&last_update, NULL);
+}
+
 void add_fsmonitor(struct index_state *istate)
 {
 	unsigned int i;
-	struct strbuf last_update = STRBUF_INIT;
 
 	if (!istate->fsmonitor_last_update) {
 		trace_printf_key(&trace_fsmonitor, "add fsmonitor");
 		istate->cache_changed |= FSMONITOR_CHANGED;
-		strbuf_addf(&last_update, "%"PRIu64"", getnanotime());
-		istate->fsmonitor_last_update = strbuf_detach(&last_update, NULL);
+		initialize_fsmonitor_last_update(istate);
 
 		/* reset the fsmonitor state */
 		for (i = 0; i < istate->cache_nr; i++)
diff --git a/fsmonitor.h b/fsmonitor.h
index 739318ab6d..7f1794b90b 100644
--- a/fsmonitor.h
+++ b/fsmonitor.h
@@ -45,6 +45,11 @@ void tweak_fsmonitor(struct index_state *istate);
 void refresh_fsmonitor(struct index_state *istate);
 
 /*
+ * Does the received result contain the "trivial" response?
+ */
+int fsmonitor_is_trivial_response(const struct strbuf *query_result);
+
+/*
  * Set the given cache entries CE_FSMONITOR_VALID bit. This should be
  * called any time the cache entry has been updated to reflect the
  * current state of the file on disk.
diff --git a/git-gui/git-gui.sh b/git-gui/git-gui.sh
index 201524c34e..236bc4e61d 100755
--- a/git-gui/git-gui.sh
+++ b/git-gui/git-gui.sh
@@ -875,6 +875,7 @@ set default_config(merge.summary) false
 set default_config(merge.verbosity) 2
 set default_config(user.name) {}
 set default_config(user.email) {}
+set default_config(core.commentchar) "#"
 
 set default_config(gui.encoding) [encoding system]
 set default_config(gui.matchtrackingbranch) false
@@ -3436,6 +3437,10 @@ proc trace_commit_type {varname args} {
 	merge         {set txt [mc "Merge Commit Message:"]}
 	*             {set txt [mc "Commit Message:"]}
 	}
+
+	set comment_char [get_config core.commentchar]
+	set txt [string cat $txt \
+				 [mc " (Lines starting with '$comment_char' will be ignored)"]]
 	$ui_coml conf -text $txt
 }
 trace add variable commit_type write trace_commit_type
diff --git a/git-gui/lib/commit.tcl b/git-gui/lib/commit.tcl
index 11379f8ad3..23d67d4651 100644
--- a/git-gui/lib/commit.tcl
+++ b/git-gui/lib/commit.tcl
@@ -141,6 +141,20 @@ proc setup_commit_encoding {msg_wt {quiet 0}} {
 	}
 }
 
+proc strip_msg {msg} {
+	set cmd [concat [list | ] [_git_cmd stripspace] --strip-comments]
+	_trace_exec $cmd
+	set fd [open $cmd r+]
+	fconfigure $fd -translation binary -encoding utf-8
+
+	puts -nonewline $fd $msg
+	close $fd w
+	set result [read $fd]
+	close $fd
+
+	return $result
+}
+
 proc commit_tree {} {
 	global HEAD commit_type file_states ui_comm repo_config
 	global pch_error
@@ -207,8 +221,8 @@ You must stage at least 1 file before you can commit.
 
 	# -- A message is required.
 	#
-	set msg [string trim [$ui_comm get 1.0 end]]
-	regsub -all -line {[ \t\r]+$} $msg {} msg
+	set msg [strip_msg [$ui_comm get 1.0 end]]
+
 	if {$msg eq {}} {
 		error_popup [mc "Please supply a commit message.
 
diff --git a/git-gui/po/ru.po b/git-gui/po/ru.po
index 161ee1ac8c..7aebaf809d 100644
--- a/git-gui/po/ru.po
+++ b/git-gui/po/ru.po
@@ -331,7 +331,7 @@ msgstr "Добавить изменённые файлы в индекс"
 
 #: git-gui.sh:2936
 msgid "Unstage From Commit"
-msgstr "Убрать из издекса"
+msgstr "Убрать из индекса"
 
 #: git-gui.sh:2942 lib/index.tcl:521
 msgid "Revert Changes"
diff --git a/http-fetch.c b/http-fetch.c
index c4ccc5fea9..fa642462a9 100644
--- a/http-fetch.c
+++ b/http-fetch.c
@@ -3,6 +3,7 @@
 #include "exec-cmd.h"
 #include "http.h"
 #include "walker.h"
+#include "strvec.h"
 
 static const char http_fetch_usage[] = "git http-fetch "
 "[-c] [-t] [-a] [-v] [--recover] [-w ref] [--stdin | --packfile=hash | commit-id] url";
@@ -44,7 +45,8 @@ static int fetch_using_walker(const char *raw_url, int get_verbosely,
 }
 
 static void fetch_single_packfile(struct object_id *packfile_hash,
-				  const char *url) {
+				  const char *url,
+				  const char **index_pack_args) {
 	struct http_pack_request *preq;
 	struct slot_results results;
 	int ret;
@@ -55,7 +57,8 @@ static void fetch_single_packfile(struct object_id *packfile_hash,
 	if (preq == NULL)
 		die("couldn't create http pack request");
 	preq->slot->results = &results;
-	preq->generate_keep = 1;
+	preq->index_pack_args = index_pack_args;
+	preq->preserve_index_pack_stdout = 1;
 
 	if (start_active_slot(preq->slot)) {
 		run_active_slot(preq->slot);
@@ -86,6 +89,7 @@ int cmd_main(int argc, const char **argv)
 	int packfile = 0;
 	int nongit;
 	struct object_id packfile_hash;
+	struct strvec index_pack_args = STRVEC_INIT;
 
 	setup_git_directory_gently(&nongit);
 
@@ -112,6 +116,8 @@ int cmd_main(int argc, const char **argv)
 			packfile = 1;
 			if (parse_oid_hex(p, &packfile_hash, &end) || *end)
 				die(_("argument to --packfile must be a valid hash (got '%s')"), p);
+		} else if (skip_prefix(argv[arg], "--index-pack-arg=", &p)) {
+			strvec_push(&index_pack_args, p);
 		}
 		arg++;
 	}
@@ -124,10 +130,18 @@ int cmd_main(int argc, const char **argv)
 	git_config(git_default_config, NULL);
 
 	if (packfile) {
-		fetch_single_packfile(&packfile_hash, argv[arg]);
+		if (!index_pack_args.nr)
+			die(_("--packfile requires --index-pack-args"));
+
+		fetch_single_packfile(&packfile_hash, argv[arg],
+				      index_pack_args.v);
+
 		return 0;
 	}
 
+	if (index_pack_args.nr)
+		die(_("--index-pack-args can only be used with --packfile"));
+
 	if (commits_on_stdin) {
 		commits = walker_targets_stdin(&commit_id, &write_ref);
 	} else {
diff --git a/http.c b/http.c
index 8b23a546af..f8ea28bb2e 100644
--- a/http.c
+++ b/http.c
@@ -2259,6 +2259,9 @@ void release_http_pack_request(struct http_pack_request *preq)
 	free(preq);
 }
 
+static const char *default_index_pack_args[] =
+	{"index-pack", "--stdin", NULL};
+
 int finish_http_pack_request(struct http_pack_request *preq)
 {
 	struct child_process ip = CHILD_PROCESS_INIT;
@@ -2270,17 +2273,15 @@ int finish_http_pack_request(struct http_pack_request *preq)
 
 	tmpfile_fd = xopen(preq->tmpfile.buf, O_RDONLY);
 
-	strvec_push(&ip.args, "index-pack");
-	strvec_push(&ip.args, "--stdin");
 	ip.git_cmd = 1;
 	ip.in = tmpfile_fd;
-	if (preq->generate_keep) {
-		strvec_pushf(&ip.args, "--keep=git %"PRIuMAX,
-			     (uintmax_t)getpid());
+	ip.argv = preq->index_pack_args ? preq->index_pack_args
+					: default_index_pack_args;
+
+	if (preq->preserve_index_pack_stdout)
 		ip.out = 0;
-	} else {
+	else
 		ip.no_stdout = 1;
-	}
 
 	if (run_command(&ip)) {
 		ret = -1;
diff --git a/http.h b/http.h
index 5de792ef3f..bf3d1270ad 100644
--- a/http.h
+++ b/http.h
@@ -218,12 +218,12 @@ struct http_pack_request {
 	char *url;
 
 	/*
-	 * If this is true, finish_http_pack_request() will pass "--keep" to
-	 * index-pack, resulting in the creation of a keep file, and will not
-	 * suppress its stdout (that is, the "keep\t<hash>\n" line will be
-	 * printed to stdout).
+	 * index-pack command to run. Must be terminated by NULL.
+	 *
+	 * If NULL, defaults to	{"index-pack", "--stdin", NULL}.
 	 */
-	unsigned generate_keep : 1;
+	const char **index_pack_args;
+	unsigned preserve_index_pack_stdout : 1;
 
 	FILE *packfile;
 	struct strbuf tmpfile;
diff --git a/merge-ort.c b/merge-ort.c
index 931b91438c..603d30c521 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -535,6 +535,23 @@ static void setup_path_info(struct merge_options *opt,
 	result->util = mi;
 }
 
+static void add_pair(struct merge_options *opt,
+		     struct name_entry *names,
+		     const char *pathname,
+		     unsigned side,
+		     unsigned is_add /* if false, is_delete */)
+{
+	struct diff_filespec *one, *two;
+	struct rename_info *renames = &opt->priv->renames;
+	int names_idx = is_add ? side : 0;
+
+	one = alloc_filespec(pathname);
+	two = alloc_filespec(pathname);
+	fill_filespec(is_add ? two : one,
+		      &names[names_idx].oid, 1, names[names_idx].mode);
+	diff_queue(&renames->pairs[side], one, two);
+}
+
 static void collect_rename_info(struct merge_options *opt,
 				struct name_entry *names,
 				const char *dirname,
@@ -544,6 +561,7 @@ static void collect_rename_info(struct merge_options *opt,
 				unsigned match_mask)
 {
 	struct rename_info *renames = &opt->priv->renames;
+	unsigned side;
 
 	/* Update dirs_removed, as needed */
 	if (dirmask == 1 || dirmask == 3 || dirmask == 5) {
@@ -554,6 +572,21 @@ static void collect_rename_info(struct merge_options *opt,
 		if (sides & 2)
 			strset_add(&renames->dirs_removed[2], fullname);
 	}
+
+	if (filemask == 0 || filemask == 7)
+		return;
+
+	for (side = MERGE_SIDE1; side <= MERGE_SIDE2; ++side) {
+		unsigned side_mask = (1 << side);
+
+		/* Check for deletion on side */
+		if ((filemask & 1) && !(filemask & side_mask))
+			add_pair(opt, names, fullname, side, 0 /* delete */);
+
+		/* Check for addition on side */
+		if (!(filemask & 1) && (filemask & side_mask))
+			add_pair(opt, names, fullname, side, 1 /* add */);
+	}
 }
 
 static int collect_merge_info_callback(int n,
@@ -2079,6 +2112,27 @@ static int process_renames(struct merge_options *opt,
 	return clean_merge;
 }
 
+static void resolve_diffpair_statuses(struct diff_queue_struct *q)
+{
+	/*
+	 * A simplified version of diff_resolve_rename_copy(); would probably
+	 * just use that function but it's static...
+	 */
+	int i;
+	struct diff_filepair *p;
+
+	for (i = 0; i < q->nr; ++i) {
+		p = q->queue[i];
+		p->status = 0; /* undecided */
+		if (!DIFF_FILE_VALID(p->one))
+			p->status = DIFF_STATUS_ADDED;
+		else if (!DIFF_FILE_VALID(p->two))
+			p->status = DIFF_STATUS_DELETED;
+		else if (DIFF_PAIR_RENAME(p))
+			p->status = DIFF_STATUS_RENAMED;
+	}
+}
+
 static int compare_pairs(const void *a_, const void *b_)
 {
 	const struct diff_filepair *a = *((const struct diff_filepair **)a_);
@@ -2089,8 +2143,6 @@ static int compare_pairs(const void *a_, const void *b_)
 
 /* Call diffcore_rename() to compute which files have changed on given side */
 static void detect_regular_renames(struct merge_options *opt,
-				   struct tree *merge_base,
-				   struct tree *side,
 				   unsigned side_index)
 {
 	struct diff_options diff_opts;
@@ -2108,11 +2160,11 @@ static void detect_regular_renames(struct merge_options *opt,
 	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
 	diff_setup_done(&diff_opts);
 
+	diff_queued_diff = renames->pairs[side_index];
 	trace2_region_enter("diff", "diffcore_rename", opt->repo);
-	diff_tree_oid(&merge_base->object.oid, &side->object.oid, "",
-		      &diff_opts);
-	diffcore_std(&diff_opts);
+	diffcore_rename(&diff_opts);
 	trace2_region_leave("diff", "diffcore_rename", opt->repo);
+	resolve_diffpair_statuses(&diff_queued_diff);
 
 	if (diff_opts.needed_rename_limit > renames->needed_limit)
 		renames->needed_limit = diff_opts.needed_rename_limit;
@@ -2212,8 +2264,8 @@ static int detect_and_process_renames(struct merge_options *opt,
 	memset(&combined, 0, sizeof(combined));
 
 	trace2_region_enter("merge", "regular renames", opt->repo);
-	detect_regular_renames(opt, merge_base, side1, MERGE_SIDE1);
-	detect_regular_renames(opt, merge_base, side2, MERGE_SIDE2);
+	detect_regular_renames(opt, MERGE_SIDE1);
+	detect_regular_renames(opt, MERGE_SIDE2);
 	trace2_region_leave("merge", "regular renames", opt->repo);
 
 	trace2_region_enter("merge", "directory renames", opt->repo);
diff --git a/midx.c b/midx.c
index 05c40a98e0..971faa8cfc 100644
--- a/midx.c
+++ b/midx.c
@@ -11,6 +11,7 @@
 #include "trace2.h"
 #include "run-command.h"
 #include "repository.h"
+#include "chunk-format.h"
 
 #define MIDX_SIGNATURE 0x4d494458 /* "MIDX" */
 #define MIDX_VERSION 1
@@ -21,14 +22,12 @@
 #define MIDX_HEADER_SIZE 12
 #define MIDX_MIN_SIZE (MIDX_HEADER_SIZE + the_hash_algo->rawsz)
 
-#define MIDX_MAX_CHUNKS 5
 #define MIDX_CHUNK_ALIGNMENT 4
 #define MIDX_CHUNKID_PACKNAMES 0x504e414d /* "PNAM" */
 #define MIDX_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
 #define MIDX_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
 #define MIDX_CHUNKID_OBJECTOFFSETS 0x4f4f4646 /* "OOFF" */
 #define MIDX_CHUNKID_LARGEOFFSETS 0x4c4f4646 /* "LOFF" */
-#define MIDX_CHUNKLOOKUP_WIDTH (sizeof(uint32_t) + sizeof(uint64_t))
 #define MIDX_CHUNK_FANOUT_SIZE (sizeof(uint32_t) * 256)
 #define MIDX_CHUNK_OFFSET_WIDTH (2 * sizeof(uint32_t))
 #define MIDX_CHUNK_LARGE_OFFSET_WIDTH (sizeof(uint64_t))
@@ -53,6 +52,19 @@ static char *get_midx_filename(const char *object_dir)
 	return xstrfmt("%s/pack/multi-pack-index", object_dir);
 }
 
+static int midx_read_oid_fanout(const unsigned char *chunk_start,
+				size_t chunk_size, void *data)
+{
+	struct multi_pack_index *m = data;
+	m->chunk_oid_fanout = (uint32_t *)chunk_start;
+
+	if (chunk_size != 4 * 256) {
+		error(_("multi-pack-index OID fanout is of the wrong size"));
+		return 1;
+	}
+	return 0;
+}
+
 struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local)
 {
 	struct multi_pack_index *m = NULL;
@@ -64,6 +76,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 	char *midx_name = get_midx_filename(object_dir);
 	uint32_t i;
 	const char *cur_pack_name;
+	struct chunkfile *cf = NULL;
 
 	fd = git_open(midx_name);
 
@@ -113,58 +126,23 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 
 	m->num_packs = get_be32(m->data + MIDX_BYTE_NUM_PACKS);
 
-	for (i = 0; i < m->num_chunks; i++) {
-		uint32_t chunk_id = get_be32(m->data + MIDX_HEADER_SIZE +
-					     MIDX_CHUNKLOOKUP_WIDTH * i);
-		uint64_t chunk_offset = get_be64(m->data + MIDX_HEADER_SIZE + 4 +
-						 MIDX_CHUNKLOOKUP_WIDTH * i);
-
-		if (chunk_offset >= m->data_len)
-			die(_("invalid chunk offset (too large)"));
-
-		switch (chunk_id) {
-			case MIDX_CHUNKID_PACKNAMES:
-				m->chunk_pack_names = m->data + chunk_offset;
-				break;
-
-			case MIDX_CHUNKID_OIDFANOUT:
-				m->chunk_oid_fanout = (uint32_t *)(m->data + chunk_offset);
-				break;
-
-			case MIDX_CHUNKID_OIDLOOKUP:
-				m->chunk_oid_lookup = m->data + chunk_offset;
-				break;
-
-			case MIDX_CHUNKID_OBJECTOFFSETS:
-				m->chunk_object_offsets = m->data + chunk_offset;
-				break;
-
-			case MIDX_CHUNKID_LARGEOFFSETS:
-				m->chunk_large_offsets = m->data + chunk_offset;
-				break;
-
-			case 0:
-				die(_("terminating multi-pack-index chunk id appears earlier than expected"));
-				break;
-
-			default:
-				/*
-				 * Do nothing on unrecognized chunks, allowing future
-				 * extensions to add optional chunks.
-				 */
-				break;
-		}
-	}
+	cf = init_chunkfile(NULL);
+
+	if (read_table_of_contents(cf, m->data, midx_size,
+				   MIDX_HEADER_SIZE, m->num_chunks))
+		goto cleanup_fail;
 
-	if (!m->chunk_pack_names)
+	if (pair_chunk(cf, MIDX_CHUNKID_PACKNAMES, &m->chunk_pack_names) == CHUNK_NOT_FOUND)
 		die(_("multi-pack-index missing required pack-name chunk"));
-	if (!m->chunk_oid_fanout)
+	if (read_chunk(cf, MIDX_CHUNKID_OIDFANOUT, midx_read_oid_fanout, m) == CHUNK_NOT_FOUND)
 		die(_("multi-pack-index missing required OID fanout chunk"));
-	if (!m->chunk_oid_lookup)
+	if (pair_chunk(cf, MIDX_CHUNKID_OIDLOOKUP, &m->chunk_oid_lookup) == CHUNK_NOT_FOUND)
 		die(_("multi-pack-index missing required OID lookup chunk"));
-	if (!m->chunk_object_offsets)
+	if (pair_chunk(cf, MIDX_CHUNKID_OBJECTOFFSETS, &m->chunk_object_offsets) == CHUNK_NOT_FOUND)
 		die(_("multi-pack-index missing required object offsets chunk"));
 
+	pair_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets);
+
 	m->num_objects = ntohl(m->chunk_oid_fanout[255]);
 
 	m->pack_names = xcalloc(m->num_packs, sizeof(*m->pack_names));
@@ -190,6 +168,7 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 cleanup_fail:
 	free(m);
 	free(midx_name);
+	free(cf);
 	if (midx_map)
 		munmap(midx_map, midx_size);
 	if (0 <= fd)
@@ -265,7 +244,7 @@ static off_t nth_midxed_offset(struct multi_pack_index *m, uint32_t pos)
 	const unsigned char *offset_data;
 	uint32_t offset32;
 
-	offset_data = m->chunk_object_offsets + pos * MIDX_CHUNK_OFFSET_WIDTH;
+	offset_data = m->chunk_object_offsets + (off_t)pos * MIDX_CHUNK_OFFSET_WIDTH;
 	offset32 = get_be32(offset_data + sizeof(uint32_t));
 
 	if (m->chunk_large_offsets && offset32 & MIDX_LARGE_OFFSET_NEEDED) {
@@ -281,7 +260,8 @@ static off_t nth_midxed_offset(struct multi_pack_index *m, uint32_t pos)
 
 static uint32_t nth_midxed_pack_int_id(struct multi_pack_index *m, uint32_t pos)
 {
-	return get_be32(m->chunk_object_offsets + pos * MIDX_CHUNK_OFFSET_WIDTH);
+	return get_be32(m->chunk_object_offsets +
+			(off_t)pos * MIDX_CHUNK_OFFSET_WIDTH);
 }
 
 static int nth_midxed_pack_entry(struct repository *r,
@@ -451,49 +431,56 @@ static int pack_info_compare(const void *_a, const void *_b)
 	return strcmp(a->pack_name, b->pack_name);
 }
 
-struct pack_list {
+struct write_midx_context {
 	struct pack_info *info;
 	uint32_t nr;
 	uint32_t alloc;
 	struct multi_pack_index *m;
 	struct progress *progress;
 	unsigned pack_paths_checked;
+
+	struct pack_midx_entry *entries;
+	uint32_t entries_nr;
+
+	uint32_t *pack_perm;
+	unsigned large_offsets_needed:1;
+	uint32_t num_large_offsets;
 };
 
 static void add_pack_to_midx(const char *full_path, size_t full_path_len,
 			     const char *file_name, void *data)
 {
-	struct pack_list *packs = (struct pack_list *)data;
+	struct write_midx_context *ctx = data;
 
 	if (ends_with(file_name, ".idx")) {
-		display_progress(packs->progress, ++packs->pack_paths_checked);
-		if (packs->m && midx_contains_pack(packs->m, file_name))
+		display_progress(ctx->progress, ++ctx->pack_paths_checked);
+		if (ctx->m && midx_contains_pack(ctx->m, file_name))
 			return;
 
-		ALLOC_GROW(packs->info, packs->nr + 1, packs->alloc);
+		ALLOC_GROW(ctx->info, ctx->nr + 1, ctx->alloc);
 
-		packs->info[packs->nr].p = add_packed_git(full_path,
-							  full_path_len,
-							  0);
+		ctx->info[ctx->nr].p = add_packed_git(full_path,
+						      full_path_len,
+						      0);
 
-		if (!packs->info[packs->nr].p) {
+		if (!ctx->info[ctx->nr].p) {
 			warning(_("failed to add packfile '%s'"),
 				full_path);
 			return;
 		}
 
-		if (open_pack_index(packs->info[packs->nr].p)) {
+		if (open_pack_index(ctx->info[ctx->nr].p)) {
 			warning(_("failed to open pack-index '%s'"),
 				full_path);
-			close_pack(packs->info[packs->nr].p);
-			FREE_AND_NULL(packs->info[packs->nr].p);
+			close_pack(ctx->info[ctx->nr].p);
+			FREE_AND_NULL(ctx->info[ctx->nr].p);
 			return;
 		}
 
-		packs->info[packs->nr].pack_name = xstrdup(file_name);
-		packs->info[packs->nr].orig_pack_int_id = packs->nr;
-		packs->info[packs->nr].expired = 0;
-		packs->nr++;
+		ctx->info[ctx->nr].pack_name = xstrdup(file_name);
+		ctx->info[ctx->nr].orig_pack_int_id = ctx->nr;
+		ctx->info[ctx->nr].expired = 0;
+		ctx->nr++;
 	}
 }
 
@@ -643,27 +630,26 @@ static struct pack_midx_entry *get_sorted_entries(struct multi_pack_index *m,
 	return deduplicated_entries;
 }
 
-static size_t write_midx_pack_names(struct hashfile *f,
-				    struct pack_info *info,
-				    uint32_t num_packs)
+static int write_midx_pack_names(struct hashfile *f, void *data)
 {
+	struct write_midx_context *ctx = data;
 	uint32_t i;
 	unsigned char padding[MIDX_CHUNK_ALIGNMENT];
 	size_t written = 0;
 
-	for (i = 0; i < num_packs; i++) {
+	for (i = 0; i < ctx->nr; i++) {
 		size_t writelen;
 
-		if (info[i].expired)
+		if (ctx->info[i].expired)
 			continue;
 
-		if (i && strcmp(info[i].pack_name, info[i - 1].pack_name) <= 0)
+		if (i && strcmp(ctx->info[i].pack_name, ctx->info[i - 1].pack_name) <= 0)
 			BUG("incorrect pack-file order: %s before %s",
-			    info[i - 1].pack_name,
-			    info[i].pack_name);
+			    ctx->info[i - 1].pack_name,
+			    ctx->info[i].pack_name);
 
-		writelen = strlen(info[i].pack_name) + 1;
-		hashwrite(f, info[i].pack_name, writelen);
+		writelen = strlen(ctx->info[i].pack_name) + 1;
+		hashwrite(f, ctx->info[i].pack_name, writelen);
 		written += writelen;
 	}
 
@@ -672,18 +658,17 @@ static size_t write_midx_pack_names(struct hashfile *f,
 	if (i < MIDX_CHUNK_ALIGNMENT) {
 		memset(padding, 0, sizeof(padding));
 		hashwrite(f, padding, i);
-		written += i;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_oid_fanout(struct hashfile *f,
-				    struct pack_midx_entry *objects,
-				    uint32_t nr_objects)
+static int write_midx_oid_fanout(struct hashfile *f,
+				 void *data)
 {
-	struct pack_midx_entry *list = objects;
-	struct pack_midx_entry *last = objects + nr_objects;
+	struct write_midx_context *ctx = data;
+	struct pack_midx_entry *list = ctx->entries;
+	struct pack_midx_entry *last = ctx->entries + ctx->entries_nr;
 	uint32_t count = 0;
 	uint32_t i;
 
@@ -704,21 +689,21 @@ static size_t write_midx_oid_fanout(struct hashfile *f,
 		list = next;
 	}
 
-	return MIDX_CHUNK_FANOUT_SIZE;
+	return 0;
 }
 
-static size_t write_midx_oid_lookup(struct hashfile *f, unsigned char hash_len,
-				    struct pack_midx_entry *objects,
-				    uint32_t nr_objects)
+static int write_midx_oid_lookup(struct hashfile *f,
+				 void *data)
 {
-	struct pack_midx_entry *list = objects;
+	struct write_midx_context *ctx = data;
+	unsigned char hash_len = the_hash_algo->rawsz;
+	struct pack_midx_entry *list = ctx->entries;
 	uint32_t i;
-	size_t written = 0;
 
-	for (i = 0; i < nr_objects; i++) {
+	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *obj = list++;
 
-		if (i < nr_objects - 1) {
+		if (i < ctx->entries_nr - 1) {
 			struct pack_midx_entry *next = list;
 			if (oidcmp(&obj->oid, &next->oid) >= 0)
 				BUG("OIDs not in order: %s >= %s",
@@ -727,50 +712,48 @@ static size_t write_midx_oid_lookup(struct hashfile *f, unsigned char hash_len,
 		}
 
 		hashwrite(f, obj->oid.hash, (int)hash_len);
-		written += hash_len;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_object_offsets(struct hashfile *f, int large_offset_needed,
-					uint32_t *perm,
-					struct pack_midx_entry *objects, uint32_t nr_objects)
+static int write_midx_object_offsets(struct hashfile *f,
+				     void *data)
 {
-	struct pack_midx_entry *list = objects;
+	struct write_midx_context *ctx = data;
+	struct pack_midx_entry *list = ctx->entries;
 	uint32_t i, nr_large_offset = 0;
-	size_t written = 0;
 
-	for (i = 0; i < nr_objects; i++) {
+	for (i = 0; i < ctx->entries_nr; i++) {
 		struct pack_midx_entry *obj = list++;
 
-		if (perm[obj->pack_int_id] == PACK_EXPIRED)
+		if (ctx->pack_perm[obj->pack_int_id] == PACK_EXPIRED)
 			BUG("object %s is in an expired pack with int-id %d",
 			    oid_to_hex(&obj->oid),
 			    obj->pack_int_id);
 
-		hashwrite_be32(f, perm[obj->pack_int_id]);
+		hashwrite_be32(f, ctx->pack_perm[obj->pack_int_id]);
 
-		if (large_offset_needed && obj->offset >> 31)
+		if (ctx->large_offsets_needed && obj->offset >> 31)
 			hashwrite_be32(f, MIDX_LARGE_OFFSET_NEEDED | nr_large_offset++);
-		else if (!large_offset_needed && obj->offset >> 32)
+		else if (!ctx->large_offsets_needed && obj->offset >> 32)
 			BUG("object %s requires a large offset (%"PRIx64") but the MIDX is not writing large offsets!",
 			    oid_to_hex(&obj->oid),
 			    obj->offset);
 		else
 			hashwrite_be32(f, (uint32_t)obj->offset);
-
-		written += MIDX_CHUNK_OFFSET_WIDTH;
 	}
 
-	return written;
+	return 0;
 }
 
-static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_offset,
-				       struct pack_midx_entry *objects, uint32_t nr_objects)
+static int write_midx_large_offsets(struct hashfile *f,
+				    void *data)
 {
-	struct pack_midx_entry *list = objects, *end = objects + nr_objects;
-	size_t written = 0;
+	struct write_midx_context *ctx = data;
+	struct pack_midx_entry *list = ctx->entries;
+	struct pack_midx_entry *end = ctx->entries + ctx->entries_nr;
+	uint32_t nr_large_offset = ctx->num_large_offsets;
 
 	while (nr_large_offset) {
 		struct pack_midx_entry *obj;
@@ -785,34 +768,26 @@ static size_t write_midx_large_offsets(struct hashfile *f, uint32_t nr_large_off
 		if (!(offset >> 31))
 			continue;
 
-		written += hashwrite_be64(f, offset);
+		hashwrite_be64(f, offset);
 
 		nr_large_offset--;
 	}
 
-	return written;
+	return 0;
 }
 
 static int write_midx_internal(const char *object_dir, struct multi_pack_index *m,
 			       struct string_list *packs_to_drop, unsigned flags)
 {
-	unsigned char cur_chunk, num_chunks = 0;
 	char *midx_name;
 	uint32_t i;
 	struct hashfile *f = NULL;
 	struct lock_file lk;
-	struct pack_list packs;
-	uint32_t *pack_perm = NULL;
-	uint64_t written = 0;
-	uint32_t chunk_ids[MIDX_MAX_CHUNKS + 1];
-	uint64_t chunk_offsets[MIDX_MAX_CHUNKS + 1];
-	uint32_t nr_entries, num_large_offsets = 0;
-	struct pack_midx_entry *entries = NULL;
-	struct progress *progress = NULL;
-	int large_offsets_needed = 0;
+	struct write_midx_context ctx = { 0 };
 	int pack_name_concat_len = 0;
 	int dropped_packs = 0;
 	int result = 0;
+	struct chunkfile *cf;
 
 	midx_name = get_midx_filename(object_dir);
 	if (safe_create_leading_directories(midx_name))
@@ -820,61 +795,62 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 			  midx_name);
 
 	if (m)
-		packs.m = m;
+		ctx.m = m;
 	else
-		packs.m = load_multi_pack_index(object_dir, 1);
-
-	packs.nr = 0;
-	packs.alloc = packs.m ? packs.m->num_packs : 16;
-	packs.info = NULL;
-	ALLOC_ARRAY(packs.info, packs.alloc);
-
-	if (packs.m) {
-		for (i = 0; i < packs.m->num_packs; i++) {
-			ALLOC_GROW(packs.info, packs.nr + 1, packs.alloc);
-
-			packs.info[packs.nr].orig_pack_int_id = i;
-			packs.info[packs.nr].pack_name = xstrdup(packs.m->pack_names[i]);
-			packs.info[packs.nr].p = NULL;
-			packs.info[packs.nr].expired = 0;
-			packs.nr++;
+		ctx.m = load_multi_pack_index(object_dir, 1);
+
+	ctx.nr = 0;
+	ctx.alloc = ctx.m ? ctx.m->num_packs : 16;
+	ctx.info = NULL;
+	ALLOC_ARRAY(ctx.info, ctx.alloc);
+
+	if (ctx.m) {
+		for (i = 0; i < ctx.m->num_packs; i++) {
+			ALLOC_GROW(ctx.info, ctx.nr + 1, ctx.alloc);
+
+			ctx.info[ctx.nr].orig_pack_int_id = i;
+			ctx.info[ctx.nr].pack_name = xstrdup(ctx.m->pack_names[i]);
+			ctx.info[ctx.nr].p = NULL;
+			ctx.info[ctx.nr].expired = 0;
+			ctx.nr++;
 		}
 	}
 
-	packs.pack_paths_checked = 0;
+	ctx.pack_paths_checked = 0;
 	if (flags & MIDX_PROGRESS)
-		packs.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
+		ctx.progress = start_delayed_progress(_("Adding packfiles to multi-pack-index"), 0);
 	else
-		packs.progress = NULL;
+		ctx.progress = NULL;
 
-	for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &packs);
-	stop_progress(&packs.progress);
+	for_each_file_in_pack_dir(object_dir, add_pack_to_midx, &ctx);
+	stop_progress(&ctx.progress);
 
-	if (packs.m && packs.nr == packs.m->num_packs && !packs_to_drop)
+	if (ctx.m && ctx.nr == ctx.m->num_packs && !packs_to_drop)
 		goto cleanup;
 
-	entries = get_sorted_entries(packs.m, packs.info, packs.nr, &nr_entries);
+	ctx.entries = get_sorted_entries(ctx.m, ctx.info, ctx.nr, &ctx.entries_nr);
 
-	for (i = 0; i < nr_entries; i++) {
-		if (entries[i].offset > 0x7fffffff)
-			num_large_offsets++;
-		if (entries[i].offset > 0xffffffff)
-			large_offsets_needed = 1;
+	ctx.large_offsets_needed = 0;
+	for (i = 0; i < ctx.entries_nr; i++) {
+		if (ctx.entries[i].offset > 0x7fffffff)
+			ctx.num_large_offsets++;
+		if (ctx.entries[i].offset > 0xffffffff)
+			ctx.large_offsets_needed = 1;
 	}
 
-	QSORT(packs.info, packs.nr, pack_info_compare);
+	QSORT(ctx.info, ctx.nr, pack_info_compare);
 
 	if (packs_to_drop && packs_to_drop->nr) {
 		int drop_index = 0;
 		int missing_drops = 0;
 
-		for (i = 0; i < packs.nr && drop_index < packs_to_drop->nr; i++) {
-			int cmp = strcmp(packs.info[i].pack_name,
+		for (i = 0; i < ctx.nr && drop_index < packs_to_drop->nr; i++) {
+			int cmp = strcmp(ctx.info[i].pack_name,
 					 packs_to_drop->items[drop_index].string);
 
 			if (!cmp) {
 				drop_index++;
-				packs.info[i].expired = 1;
+				ctx.info[i].expired = 1;
 			} else if (cmp > 0) {
 				error(_("did not see pack-file %s to drop"),
 				      packs_to_drop->items[drop_index].string);
@@ -882,7 +858,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 				missing_drops++;
 				i--;
 			} else {
-				packs.info[i].expired = 0;
+				ctx.info[i].expired = 0;
 			}
 		}
 
@@ -898,19 +874,19 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	 *
 	 * pack_perm[old_id] = new_id
 	 */
-	ALLOC_ARRAY(pack_perm, packs.nr);
-	for (i = 0; i < packs.nr; i++) {
-		if (packs.info[i].expired) {
+	ALLOC_ARRAY(ctx.pack_perm, ctx.nr);
+	for (i = 0; i < ctx.nr; i++) {
+		if (ctx.info[i].expired) {
 			dropped_packs++;
-			pack_perm[packs.info[i].orig_pack_int_id] = PACK_EXPIRED;
+			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = PACK_EXPIRED;
 		} else {
-			pack_perm[packs.info[i].orig_pack_int_id] = i - dropped_packs;
+			ctx.pack_perm[ctx.info[i].orig_pack_int_id] = i - dropped_packs;
 		}
 	}
 
-	for (i = 0; i < packs.nr; i++) {
-		if (!packs.info[i].expired)
-			pack_name_concat_len += strlen(packs.info[i].pack_name) + 1;
+	for (i = 0; i < ctx.nr; i++) {
+		if (!ctx.info[i].expired)
+			pack_name_concat_len += strlen(ctx.info[i].pack_name) + 1;
 	}
 
 	if (pack_name_concat_len % MIDX_CHUNK_ALIGNMENT)
@@ -921,123 +897,52 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 	f = hashfd(get_lock_file_fd(&lk), get_lock_file_path(&lk));
 	FREE_AND_NULL(midx_name);
 
-	if (packs.m)
-		close_midx(packs.m);
-
-	cur_chunk = 0;
-	num_chunks = large_offsets_needed ? 5 : 4;
+	if (ctx.m)
+		close_midx(ctx.m);
 
-	if (packs.nr - dropped_packs == 0) {
+	if (ctx.nr - dropped_packs == 0) {
 		error(_("no pack files to index."));
 		result = 1;
 		goto cleanup;
 	}
 
-	written = write_midx_header(f, num_chunks, packs.nr - dropped_packs);
-
-	chunk_ids[cur_chunk] = MIDX_CHUNKID_PACKNAMES;
-	chunk_offsets[cur_chunk] = written + (num_chunks + 1) * MIDX_CHUNKLOOKUP_WIDTH;
-
-	cur_chunk++;
-	chunk_ids[cur_chunk] = MIDX_CHUNKID_OIDFANOUT;
-	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + pack_name_concat_len;
-
-	cur_chunk++;
-	chunk_ids[cur_chunk] = MIDX_CHUNKID_OIDLOOKUP;
-	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + MIDX_CHUNK_FANOUT_SIZE;
-
-	cur_chunk++;
-	chunk_ids[cur_chunk] = MIDX_CHUNKID_OBJECTOFFSETS;
-	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + nr_entries * the_hash_algo->rawsz;
-
-	cur_chunk++;
-	chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] + nr_entries * MIDX_CHUNK_OFFSET_WIDTH;
-	if (large_offsets_needed) {
-		chunk_ids[cur_chunk] = MIDX_CHUNKID_LARGEOFFSETS;
-
-		cur_chunk++;
-		chunk_offsets[cur_chunk] = chunk_offsets[cur_chunk - 1] +
-					   num_large_offsets * MIDX_CHUNK_LARGE_OFFSET_WIDTH;
-	}
-
-	chunk_ids[cur_chunk] = 0;
+	cf = init_chunkfile(f);
 
-	for (i = 0; i <= num_chunks; i++) {
-		if (i && chunk_offsets[i] < chunk_offsets[i - 1])
-			BUG("incorrect chunk offsets: %"PRIu64" before %"PRIu64,
-			    chunk_offsets[i - 1],
-			    chunk_offsets[i]);
+	add_chunk(cf, MIDX_CHUNKID_PACKNAMES, pack_name_concat_len,
+		  write_midx_pack_names);
+	add_chunk(cf, MIDX_CHUNKID_OIDFANOUT, MIDX_CHUNK_FANOUT_SIZE,
+		  write_midx_oid_fanout);
+	add_chunk(cf, MIDX_CHUNKID_OIDLOOKUP,
+		  (size_t)ctx.entries_nr * the_hash_algo->rawsz,
+		  write_midx_oid_lookup);
+	add_chunk(cf, MIDX_CHUNKID_OBJECTOFFSETS,
+		  (size_t)ctx.entries_nr * MIDX_CHUNK_OFFSET_WIDTH,
+		  write_midx_object_offsets);
 
-		if (chunk_offsets[i] % MIDX_CHUNK_ALIGNMENT)
-			BUG("chunk offset %"PRIu64" is not properly aligned",
-			    chunk_offsets[i]);
-
-		hashwrite_be32(f, chunk_ids[i]);
-		hashwrite_be64(f, chunk_offsets[i]);
-
-		written += MIDX_CHUNKLOOKUP_WIDTH;
-	}
-
-	if (flags & MIDX_PROGRESS)
-		progress = start_delayed_progress(_("Writing chunks to multi-pack-index"),
-					  num_chunks);
-	for (i = 0; i < num_chunks; i++) {
-		if (written != chunk_offsets[i])
-			BUG("incorrect chunk offset (%"PRIu64" != %"PRIu64") for chunk id %"PRIx32,
-			    chunk_offsets[i],
-			    written,
-			    chunk_ids[i]);
-
-		switch (chunk_ids[i]) {
-			case MIDX_CHUNKID_PACKNAMES:
-				written += write_midx_pack_names(f, packs.info, packs.nr);
-				break;
-
-			case MIDX_CHUNKID_OIDFANOUT:
-				written += write_midx_oid_fanout(f, entries, nr_entries);
-				break;
-
-			case MIDX_CHUNKID_OIDLOOKUP:
-				written += write_midx_oid_lookup(f, the_hash_algo->rawsz, entries, nr_entries);
-				break;
-
-			case MIDX_CHUNKID_OBJECTOFFSETS:
-				written += write_midx_object_offsets(f, large_offsets_needed, pack_perm, entries, nr_entries);
-				break;
-
-			case MIDX_CHUNKID_LARGEOFFSETS:
-				written += write_midx_large_offsets(f, num_large_offsets, entries, nr_entries);
-				break;
-
-			default:
-				BUG("trying to write unknown chunk id %"PRIx32,
-				    chunk_ids[i]);
-		}
-
-		display_progress(progress, i + 1);
-	}
-	stop_progress(&progress);
+	if (ctx.large_offsets_needed)
+		add_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS,
+			(size_t)ctx.num_large_offsets * MIDX_CHUNK_LARGE_OFFSET_WIDTH,
+			write_midx_large_offsets);
 
-	if (written != chunk_offsets[num_chunks])
-		BUG("incorrect final offset %"PRIu64" != %"PRIu64,
-		    written,
-		    chunk_offsets[num_chunks]);
+	write_midx_header(f, get_num_chunks(cf), ctx.nr - dropped_packs);
+	write_chunkfile(cf, &ctx);
 
 	finalize_hashfile(f, NULL, CSUM_FSYNC | CSUM_HASH_IN_STREAM);
+	free_chunkfile(cf);
 	commit_lock_file(&lk);
 
 cleanup:
-	for (i = 0; i < packs.nr; i++) {
-		if (packs.info[i].p) {
-			close_pack(packs.info[i].p);
-			free(packs.info[i].p);
+	for (i = 0; i < ctx.nr; i++) {
+		if (ctx.info[i].p) {
+			close_pack(ctx.info[i].p);
+			free(ctx.info[i].p);
 		}
-		free(packs.info[i].pack_name);
+		free(ctx.info[i].pack_name);
 	}
 
-	free(packs.info);
-	free(entries);
-	free(pack_perm);
+	free(ctx.info);
+	free(ctx.entries);
+	free(ctx.pack_perm);
 	free(midx_name);
 	return result;
 }
diff --git a/pack-write.c b/pack-write.c
index 680c36755d..2ca85a9d16 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -380,7 +380,7 @@ void fixup_pack_header_footer(int pack_fd,
 	fsync_or_die(pack_fd, pack_name);
 }
 
-char *index_pack_lockfile(int ip_out)
+char *index_pack_lockfile(int ip_out, int *is_well_formed)
 {
 	char packname[GIT_MAX_HEXSZ + 6];
 	const int len = the_hash_algo->hexsz + 6;
@@ -394,11 +394,17 @@ char *index_pack_lockfile(int ip_out)
 	 */
 	if (read_in_full(ip_out, packname, len) == len && packname[len-1] == '\n') {
 		const char *name;
+
+		if (is_well_formed)
+			*is_well_formed = 1;
 		packname[len-1] = 0;
 		if (skip_prefix(packname, "keep\t", &name))
 			return xstrfmt("%s/pack/pack-%s.keep",
 				       get_object_directory(), name);
+		return NULL;
 	}
+	if (is_well_formed)
+		*is_well_formed = 0;
 	return NULL;
 }
 
diff --git a/pack.h b/pack.h
index afdcf8f5c7..857cbd5bd4 100644
--- a/pack.h
+++ b/pack.h
@@ -87,7 +87,7 @@ int verify_pack_index(struct packed_git *);
 int verify_pack(struct repository *, struct packed_git *, verify_fn fn, struct progress *, uint32_t);
 off_t write_pack_header(struct hashfile *f, uint32_t);
 void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t, unsigned char *, off_t);
-char *index_pack_lockfile(int fd);
+char *index_pack_lockfile(int fd, int *is_well_formed);
 
 struct ref;
 
diff --git a/preload-index.c b/preload-index.c
index ed6eaa4738..e5529a5863 100644
--- a/preload-index.c
+++ b/preload-index.c
@@ -31,6 +31,7 @@ struct thread_data {
 	struct pathspec pathspec;
 	struct progress_data *progress;
 	int offset, nr;
+	int t2_nr_lstat;
 };
 
 static void *preload_thread(void *_data)
@@ -73,6 +74,7 @@ static void *preload_thread(void *_data)
 			continue;
 		if (threaded_has_symlink_leading_path(&cache, ce->name, ce_namelen(ce)))
 			continue;
+		p->t2_nr_lstat++;
 		if (lstat(ce->name, &st))
 			continue;
 		if (ie_match_stat(index, ce, &st, CE_MATCH_RACY_IS_DIRTY|CE_MATCH_IGNORE_FSMONITOR))
@@ -98,6 +100,7 @@ void preload_index(struct index_state *index,
 	int threads, i, work, offset;
 	struct thread_data data[MAX_PARALLEL];
 	struct progress_data pd;
+	int t2_sum_lstat = 0;
 
 	if (!HAVE_THREADS || !core_preload_index)
 		return;
@@ -107,6 +110,9 @@ void preload_index(struct index_state *index,
 		threads = 2;
 	if (threads < 2)
 		return;
+
+	trace2_region_enter("index", "preload", NULL);
+
 	trace_performance_enter();
 	if (threads > MAX_PARALLEL)
 		threads = MAX_PARALLEL;
@@ -141,10 +147,14 @@ void preload_index(struct index_state *index,
 		struct thread_data *p = data+i;
 		if (pthread_join(p->pthread, NULL))
 			die("unable to join threaded lstat");
+		t2_sum_lstat += p->t2_nr_lstat;
 	}
 	stop_progress(&pd.progress);
 
 	trace_performance_leave("preload index");
+
+	trace2_data_intmax("index", NULL, "preload/sum_lstat", t2_sum_lstat);
+	trace2_region_leave("index", "preload", NULL);
 }
 
 int repo_read_index_preload(struct repository *repo,
diff --git a/pretty.c b/pretty.c
index b4ff3f602f..c5f5ecc40d 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1149,6 +1149,63 @@ static int format_trailer_match_cb(const struct strbuf *key, void *ud)
 	return 0;
 }
 
+int format_set_trailers_options(struct process_trailer_options *opts,
+				struct string_list *filter_list,
+				struct strbuf *sepbuf,
+				struct strbuf *kvsepbuf,
+				const char **arg,
+				char **invalid_arg)
+{
+	for (;;) {
+		const char *argval;
+		size_t arglen;
+
+		if (**arg == ')')
+			break;
+
+		if (match_placeholder_arg_value(*arg, "key", arg, &argval, &arglen)) {
+			uintptr_t len = arglen;
+
+			if (!argval)
+				return -1;
+
+			if (len && argval[len - 1] == ':')
+				len--;
+			string_list_append(filter_list, argval)->util = (char *)len;
+
+			opts->filter = format_trailer_match_cb;
+			opts->filter_data = filter_list;
+			opts->only_trailers = 1;
+		} else if (match_placeholder_arg_value(*arg, "separator", arg, &argval, &arglen)) {
+			char *fmt;
+
+			strbuf_reset(sepbuf);
+			fmt = xstrndup(argval, arglen);
+			strbuf_expand(sepbuf, fmt, strbuf_expand_literal_cb, NULL);
+			free(fmt);
+			opts->separator = sepbuf;
+		} else if (match_placeholder_arg_value(*arg, "key_value_separator", arg, &argval, &arglen)) {
+			char *fmt;
+
+			strbuf_reset(kvsepbuf);
+			fmt = xstrndup(argval, arglen);
+			strbuf_expand(kvsepbuf, fmt, strbuf_expand_literal_cb, NULL);
+			free(fmt);
+			opts->key_value_separator = kvsepbuf;
+		} else if (!match_placeholder_bool_arg(*arg, "only", arg, &opts->only_trailers) &&
+			   !match_placeholder_bool_arg(*arg, "unfold", arg, &opts->unfold) &&
+			   !match_placeholder_bool_arg(*arg, "keyonly", arg, &opts->key_only) &&
+			   !match_placeholder_bool_arg(*arg, "valueonly", arg, &opts->value_only)) {
+			if (invalid_arg) {
+				size_t len = strcspn(*arg, ",)");
+				*invalid_arg = xstrndup(*arg, len);
+			}
+			return -1;
+		}
+	}
+	return 0;
+}
+
 static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 				const char *placeholder,
 				void *context)
@@ -1429,45 +1486,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 
 		if (*arg == ':') {
 			arg++;
-			for (;;) {
-				const char *argval;
-				size_t arglen;
-
-				if (match_placeholder_arg_value(arg, "key", &arg, &argval, &arglen)) {
-					uintptr_t len = arglen;
-
-					if (!argval)
-						goto trailer_out;
-
-					if (len && argval[len - 1] == ':')
-						len--;
-					string_list_append(&filter_list, argval)->util = (char *)len;
-
-					opts.filter = format_trailer_match_cb;
-					opts.filter_data = &filter_list;
-					opts.only_trailers = 1;
-				} else if (match_placeholder_arg_value(arg, "separator", &arg, &argval, &arglen)) {
-					char *fmt;
-
-					strbuf_reset(&sepbuf);
-					fmt = xstrndup(argval, arglen);
-					strbuf_expand(&sepbuf, fmt, strbuf_expand_literal_cb, NULL);
-					free(fmt);
-					opts.separator = &sepbuf;
-				} else if (match_placeholder_arg_value(arg, "key_value_separator", &arg, &argval, &arglen)) {
-					char *fmt;
-
-					strbuf_reset(&kvsepbuf);
-					fmt = xstrndup(argval, arglen);
-					strbuf_expand(&kvsepbuf, fmt, strbuf_expand_literal_cb, NULL);
-					free(fmt);
-					opts.key_value_separator = &kvsepbuf;
-				} else if (!match_placeholder_bool_arg(arg, "only", &arg, &opts.only_trailers) &&
-					   !match_placeholder_bool_arg(arg, "unfold", &arg, &opts.unfold) &&
-					   !match_placeholder_bool_arg(arg, "keyonly", &arg, &opts.key_only) &&
-					   !match_placeholder_bool_arg(arg, "valueonly", &arg, &opts.value_only))
-					break;
-			}
+			if (format_set_trailers_options(&opts, &filter_list, &sepbuf, &kvsepbuf, &arg, NULL))
+				goto trailer_out;
 		}
 		if (*arg == ')') {
 			format_trailers_from_commit(sb, msg + c->subject_off, &opts);
diff --git a/pretty.h b/pretty.h
index 7ce6c0b437..d902cdd70a 100644
--- a/pretty.h
+++ b/pretty.h
@@ -6,6 +6,7 @@
 
 struct commit;
 struct strbuf;
+struct process_trailer_options;
 
 /* Commit formats */
 enum cmit_fmt {
@@ -142,4 +143,15 @@ int commit_format_is_empty(enum cmit_fmt);
 /* Make subject of commit message suitable for filename */
 void format_sanitized_subject(struct strbuf *sb, const char *msg, size_t len);
 
+/*
+ * Set values of fields in "struct process_trailer_options"
+ * according to trailers arguments.
+ */
+int format_set_trailers_options(struct process_trailer_options *opts,
+			struct string_list *filter_list,
+			struct strbuf *sepbuf,
+			struct strbuf *kvsepbuf,
+			const char **arg,
+			char **invalid_arg);
+
 #endif /* PRETTY_H */
diff --git a/read-cache.c b/read-cache.c
index 29144cf879..1e9a50c6c7 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1364,7 +1364,9 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 					     struct cache_entry *ce,
 					     unsigned int options, int *err,
-					     int *changed_ret)
+					     int *changed_ret,
+					     int *t2_did_lstat,
+					     int *t2_did_scan)
 {
 	struct stat st;
 	struct cache_entry *updated;
@@ -1406,6 +1408,8 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		return NULL;
 	}
 
+	if (t2_did_lstat)
+		*t2_did_lstat = 1;
 	if (lstat(ce->name, &st) < 0) {
 		if (ignore_missing && errno == ENOENT)
 			return ce;
@@ -1442,6 +1446,8 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		}
 	}
 
+	if (t2_did_scan)
+		*t2_did_scan = 1;
 	if (ie_modified(istate, ce, &st, options)) {
 		if (err)
 			*err = EINVAL;
@@ -1519,6 +1525,8 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	const char *added_fmt;
 	const char *unmerged_fmt;
 	struct progress *progress = NULL;
+	int t2_sum_lstat = 0;
+	int t2_sum_scan = 0;
 
 	if (flags & REFRESH_PROGRESS && isatty(2))
 		progress = start_delayed_progress(_("Refresh index"),
@@ -1536,11 +1544,14 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	 * we only have to do the special cases that are left.
 	 */
 	preload_index(istate, pathspec, 0);
+	trace2_region_enter("index", "refresh", NULL);
 	for (i = 0; i < istate->cache_nr; i++) {
 		struct cache_entry *ce, *new_entry;
 		int cache_errno = 0;
 		int changed = 0;
 		int filtered = 0;
+		int t2_did_lstat = 0;
+		int t2_did_scan = 0;
 
 		ce = istate->cache[i];
 		if (ignore_submodules && S_ISGITLINK(ce->ce_mode))
@@ -1566,7 +1577,11 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 		if (filtered)
 			continue;
 
-		new_entry = refresh_cache_ent(istate, ce, options, &cache_errno, &changed);
+		new_entry = refresh_cache_ent(istate, ce, options,
+					      &cache_errno, &changed,
+					      &t2_did_lstat, &t2_did_scan);
+		t2_sum_lstat += t2_did_lstat;
+		t2_sum_scan += t2_did_scan;
 		if (new_entry == ce)
 			continue;
 		if (progress)
@@ -1602,6 +1617,9 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 
 		replace_index_entry(istate, i, new_entry);
 	}
+	trace2_data_intmax("index", NULL, "refresh/sum_lstat", t2_sum_lstat);
+	trace2_data_intmax("index", NULL, "refresh/sum_scan", t2_sum_scan);
+	trace2_region_leave("index", "refresh", NULL);
 	if (progress) {
 		display_progress(progress, istate->cache_nr);
 		stop_progress(&progress);
@@ -1614,7 +1632,7 @@ struct cache_entry *refresh_cache_entry(struct index_state *istate,
 					struct cache_entry *ce,
 					unsigned int options)
 {
-	return refresh_cache_ent(istate, ce, options, NULL, NULL);
+	return refresh_cache_ent(istate, ce, options, NULL, NULL, NULL, NULL);
 }
 
 
@@ -2447,7 +2465,7 @@ int repo_index_has_changes(struct repository *repo,
 	}
 }
 
-#define WRITE_BUFFER_SIZE 8192
+#define WRITE_BUFFER_SIZE (128 * 1024)
 static unsigned char write_buffer[WRITE_BUFFER_SIZE];
 static unsigned long write_buffer_len;
 
diff --git a/ref-filter.c b/ref-filter.c
index bade6528ee..e84efb53db 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -67,6 +67,12 @@ struct refname_atom {
 	int lstrip, rstrip;
 };
 
+static struct ref_trailer_buf {
+	struct string_list filter_list;
+	struct strbuf sepbuf;
+	struct strbuf kvsepbuf;
+} ref_trailer_buf = {STRING_LIST_INIT_NODUP, STRBUF_INIT, STRBUF_INIT};
+
 static struct expand_data {
 	struct object_id oid;
 	enum object_type type;
@@ -313,28 +319,26 @@ static int subject_atom_parser(const struct ref_format *format, struct used_atom
 static int trailers_atom_parser(const struct ref_format *format, struct used_atom *atom,
 				const char *arg, struct strbuf *err)
 {
-	struct string_list params = STRING_LIST_INIT_DUP;
-	int i;
-
 	atom->u.contents.trailer_opts.no_divider = 1;
 
 	if (arg) {
-		string_list_split(&params, arg, ',', -1);
-		for (i = 0; i < params.nr; i++) {
-			const char *s = params.items[i].string;
-			if (!strcmp(s, "unfold"))
-				atom->u.contents.trailer_opts.unfold = 1;
-			else if (!strcmp(s, "only"))
-				atom->u.contents.trailer_opts.only_trailers = 1;
-			else {
-				strbuf_addf(err, _("unknown %%(trailers) argument: %s"), s);
-				string_list_clear(&params, 0);
-				return -1;
-			}
+		const char *argbuf = xstrfmt("%s)", arg);
+		char *invalid_arg = NULL;
+
+		if (format_set_trailers_options(&atom->u.contents.trailer_opts,
+		    &ref_trailer_buf.filter_list,
+		    &ref_trailer_buf.sepbuf,
+		    &ref_trailer_buf.kvsepbuf,
+		    &argbuf, &invalid_arg)) {
+			if (!invalid_arg)
+				strbuf_addf(err, _("expected %%(trailers:key=<value>)"));
+			else
+				strbuf_addf(err, _("unknown %%(trailers) argument: %s"), invalid_arg);
+			free((char *)invalid_arg);
+			return -1;
 		}
 	}
 	atom->u.contents.option = C_TRAILERS;
-	string_list_clear(&params, 0);
 	return 0;
 }
 
diff --git a/t/perf/.gitignore b/t/perf/.gitignore
index 982eb8e3a9..72f5d0d314 100644
--- a/t/perf/.gitignore
+++ b/t/perf/.gitignore
@@ -1,3 +1,4 @@
 /build/
 /test-results/
+/test-trace/
 /trash directory*/
diff --git a/t/perf/Makefile b/t/perf/Makefile
index fcb0e8865e..2465770a78 100644
--- a/t/perf/Makefile
+++ b/t/perf/Makefile
@@ -7,10 +7,10 @@ perf: pre-clean
 	./run
 
 pre-clean:
-	rm -rf test-results
+	rm -rf test-results test-trace
 
 clean:
-	rm -rf build "trash directory".* test-results
+	rm -rf build "trash directory".* test-results test-trace
 
 test-lint:
 	$(MAKE) -C .. test-lint
diff --git a/t/perf/p7519-fsmonitor.sh b/t/perf/p7519-fsmonitor.sh
index 1e20a184c7..b657564aed 100755
--- a/t/perf/p7519-fsmonitor.sh
+++ b/t/perf/p7519-fsmonitor.sh
@@ -32,6 +32,8 @@ test_description="Test core.fsmonitor"
 #
 # GIT_PERF_7519_DROP_CACHE: if set, the OS caches are dropped between tests
 #
+# GIT_PERF_7519_TRACE: if set, enable trace logging during the test.
+#   Trace logs will be grouped by fsmonitor provider.
 
 test_perf_large_repo
 test_checkout_worktree
@@ -70,6 +72,32 @@ then
 	fi
 fi
 
+trace_start() {
+	if test -n "$GIT_PERF_7519_TRACE"
+	then
+		name="$1"
+		TEST_TRACE_DIR="$TEST_OUTPUT_DIRECTORY/test-trace/p7519/"
+		echo "Writing trace logging to $TEST_TRACE_DIR"
+
+		mkdir -p "$TEST_TRACE_DIR"
+
+		# Start Trace2 logging and any other GIT_TRACE_* logs that you
+		# want for this named test case.
+
+		GIT_TRACE2_PERF="$TEST_TRACE_DIR/$name.trace2perf"
+		export GIT_TRACE2_PERF
+
+		>"$GIT_TRACE2_PERF"
+	fi
+}
+
+trace_stop() {
+	if test -n "$GIT_PERF_7519_TRACE"
+	then
+		unset GIT_TRACE2_PERF
+	fi
+}
+
 test_expect_success "one time repo setup" '
 	# set untrackedCache depending on the environment
 	if test -n "$GIT_PERF_7519_UNTRACKED_CACHE"
@@ -101,7 +129,7 @@ test_expect_success "one time repo setup" '
 	# If Watchman exists, watch the work tree and attempt a query.
 	if test_have_prereq WATCHMAN; then
 		watchman watch "$GIT_WORK_TREE" &&
-		watchman watch-list | grep -q -F "$GIT_WORK_TREE"
+		watchman watch-list | grep -q -F "p7519-fsmonitor"
 	fi
 '
 
@@ -169,8 +197,18 @@ test_fsmonitor_suite() {
 		git status -uall
 	'
 
+	# Update the mtimes on upto 100k files to make status think
+	# that they are dirty.  For simplicity, omit any files with
+	# LFs (i.e. anything that ls-files thinks it needs to dquote).
+	# Then fully backslash-quote the paths to capture any
+	# whitespace so that they pass thru xargs properly.
+	#
 	test_perf_w_drop_caches "status (dirty) ($DESC)" '
-		git ls-files | head -100000 | xargs -d "\n" touch -h &&
+		git ls-files | \
+			head -100000 | \
+			grep -v \" | \
+			sed '\''s/\(.\)/\\\1/g'\'' | \
+			xargs test-tool chmtime -300 &&
 		git status
 	'
 
@@ -203,6 +241,12 @@ test_fsmonitor_suite() {
 	'
 }
 
+#
+# Run a full set of perf tests using each Hook-based fsmonitor provider,
+# such as Watchman.
+#
+
+trace_start fsmonitor-watchman
 if test -n "$GIT_PERF_7519_FSMONITOR"; then
 	for INTEGRATION_PATH in $GIT_PERF_7519_FSMONITOR; do
 		test_expect_success "setup for fsmonitor $INTEGRATION_PATH" 'setup_for_fsmonitor'
@@ -213,14 +257,6 @@ else
 	test_fsmonitor_suite
 fi
 
-test_expect_success "setup without fsmonitor" '
-	unset INTEGRATION_SCRIPT &&
-	git config --unset core.fsmonitor &&
-	git update-index --no-fsmonitor
-'
-
-test_fsmonitor_suite
-
 if test_have_prereq WATCHMAN
 then
 	watchman watch-del "$GIT_WORK_TREE" >/dev/null 2>&1 &&
@@ -229,5 +265,20 @@ then
 	# preventing the removal of the trash directory
 	watchman shutdown-server >/dev/null 2>&1
 fi
+trace_stop
+
+#
+# Run a full set of perf tests with the fsmonitor feature disabled.
+#
+
+trace_start fsmonitor-disabled
+test_expect_success "setup without fsmonitor" '
+	unset INTEGRATION_SCRIPT &&
+	git config --unset core.fsmonitor &&
+	git update-index --no-fsmonitor
+'
+
+test_fsmonitor_suite
+trace_stop
 
 test_done
diff --git a/t/t4001-diff-rename.sh b/t/t4001-diff-rename.sh
index 2f9700742a..68f2ebca58 100755
--- a/t/t4001-diff-rename.sh
+++ b/t/t4001-diff-rename.sh
@@ -262,4 +262,28 @@ test_expect_success 'diff-tree -l0 defaults to a big rename limit, not zero' '
 	grep "myotherfile.*myfile" actual
 '
 
+test_expect_success 'basename similarity vs best similarity' '
+	mkdir subdir &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			 line6 line7 line8 line9 line10 >subdir/file.txt &&
+	git add subdir/file.txt &&
+	git commit -m "base txt" &&
+
+	git rm subdir/file.txt &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			  line6 line7 line8 >file.txt &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			  line6 line7 line8 line9 >file.md &&
+	git add file.txt file.md &&
+	git commit -a -m "rename" &&
+	git diff-tree -r -M --name-status HEAD^ HEAD >actual &&
+	# subdir/file.txt is 88% similar to file.md, 78% similar to file.txt,
+	# but since same basenames are checked first...
+	cat >expected <<-\EOF &&
+	A	file.md
+	R078	subdir/file.txt	file.txt
+	EOF
+	test_cmp expected actual
+'
+
 test_done
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index fa2ba93fe8..edeb6d6d31 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -585,7 +585,7 @@ test_expect_success 'detect bad hash version' '
 
 test_expect_success 'detect low chunk count' '
 	corrupt_graph_and_verify $GRAPH_BYTE_CHUNK_COUNT "\01" \
-		"missing the .* chunk"
+		"final chunk has non-zero id"
 '
 
 test_expect_success 'detect missing OID fanout chunk' '
diff --git a/t/t5319-multi-pack-index.sh b/t/t5319-multi-pack-index.sh
index 2fc3aadbd1..b4afab1dfc 100755
--- a/t/t5319-multi-pack-index.sh
+++ b/t/t5319-multi-pack-index.sh
@@ -314,12 +314,12 @@ test_expect_success 'verify bad OID version' '
 
 test_expect_success 'verify truncated chunk count' '
 	corrupt_midx_and_verify $MIDX_BYTE_CHUNK_COUNT "\01" $objdir \
-		"missing required"
+		"final chunk has non-zero id"
 '
 
 test_expect_success 'verify extended chunk count' '
 	corrupt_midx_and_verify $MIDX_BYTE_CHUNK_COUNT "\07" $objdir \
-		"terminating multi-pack-index chunk id appears earlier than expected"
+		"terminating chunk id appears earlier than expected"
 '
 
 test_expect_success 'verify missing required chunk' '
@@ -329,7 +329,7 @@ test_expect_success 'verify missing required chunk' '
 
 test_expect_success 'verify invalid chunk offset' '
 	corrupt_midx_and_verify $MIDX_BYTE_CHUNK_OFFSET "\01" $objdir \
-		"invalid chunk offset (too large)"
+		"improper chunk offset(s)"
 '
 
 test_expect_success 'verify packnames out of order' '
diff --git a/t/t5550-http-fetch-dumb.sh b/t/t5550-http-fetch-dumb.sh
index 2ecb06bb63..6d9142afc3 100755
--- a/t/t5550-http-fetch-dumb.sh
+++ b/t/t5550-http-fetch-dumb.sh
@@ -227,7 +227,10 @@ test_expect_success 'http-fetch --packfile' '
 
 	git init packfileclient &&
 	p=$(cd "$HTTPD_DOCUMENT_ROOT_PATH"/repo_pack.git && ls objects/pack/pack-*.pack) &&
-	git -C packfileclient http-fetch --packfile=$ARBITRARY "$HTTPD_URL"/dumb/repo_pack.git/$p >out &&
+	git -C packfileclient http-fetch --packfile=$ARBITRARY \
+		--index-pack-arg=index-pack --index-pack-arg=--stdin \
+		--index-pack-arg=--keep \
+		"$HTTPD_URL"/dumb/repo_pack.git/$p >out &&
 
 	grep "^keep.[0-9a-f]\{16,\}$" out &&
 	cut -c6- out >packhash &&
diff --git a/t/t5702-protocol-v2.sh b/t/t5702-protocol-v2.sh
index 9113d209c5..994a76ca3c 100755
--- a/t/t5702-protocol-v2.sh
+++ b/t/t5702-protocol-v2.sh
@@ -875,11 +875,10 @@ test_expect_success 'part of packfile response provided as URI' '
 	test -f hfound &&
 	test -f h2found &&
 
-	# Ensure that there are exactly 6 files (3 .pack and 3 .idx).
-	ls http_child/.git/objects/pack/*.pack >packlist &&
-	ls http_child/.git/objects/pack/*.idx >idxlist &&
-	test_line_count = 3 idxlist &&
-	test_line_count = 3 packlist
+	# Ensure that there are exactly 3 packfiles with associated .idx
+	ls http_child/.git/objects/pack/*.pack \
+	    http_child/.git/objects/pack/*.idx >filelist &&
+	test_line_count = 6 filelist
 '
 
 test_expect_success 'fetching with valid packfile URI but invalid hash fails' '
@@ -931,11 +930,10 @@ test_expect_success 'packfile-uri with transfer.fsckobjects' '
 		-c fetch.uriprotocols=http,https \
 		clone "$HTTPD_URL/smart/http_parent" http_child &&
 
-	# Ensure that there are exactly 4 files (2 .pack and 2 .idx).
-	ls http_child/.git/objects/pack/*.pack >packlist &&
-	ls http_child/.git/objects/pack/*.idx >idxlist &&
-	test_line_count = 2 idxlist &&
-	test_line_count = 2 packlist
+	# Ensure that there are exactly 2 packfiles with associated .idx
+	ls http_child/.git/objects/pack/*.pack \
+	    http_child/.git/objects/pack/*.idx >filelist &&
+	test_line_count = 4 filelist
 '
 
 test_expect_success 'packfile-uri with transfer.fsckobjects fails on bad object' '
@@ -968,6 +966,54 @@ test_expect_success 'packfile-uri with transfer.fsckobjects fails on bad object'
 	test_i18ngrep "invalid author/committer line - missing email" error
 '
 
+test_expect_success 'packfile-uri with transfer.fsckobjects succeeds when .gitmodules is separate from tree' '
+	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
+	rm -rf "$P" http_child &&
+
+	git init "$P" &&
+	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
+
+	echo "[submodule libfoo]" >"$P/.gitmodules" &&
+	echo "path = include/foo" >>"$P/.gitmodules" &&
+	echo "url = git://example.com/git/lib.git" >>"$P/.gitmodules" &&
+	git -C "$P" add .gitmodules &&
+	git -C "$P" commit -m x &&
+
+	configure_exclusion "$P" .gitmodules >h &&
+
+	sane_unset GIT_TEST_SIDEBAND_ALL &&
+	git -c protocol.version=2 -c transfer.fsckobjects=1 \
+		-c fetch.uriprotocols=http,https \
+		clone "$HTTPD_URL/smart/http_parent" http_child &&
+
+	# Ensure that there are exactly 2 packfiles with associated .idx
+	ls http_child/.git/objects/pack/*.pack \
+	    http_child/.git/objects/pack/*.idx >filelist &&
+	test_line_count = 4 filelist
+'
+
+test_expect_success 'packfile-uri with transfer.fsckobjects fails when .gitmodules separate from tree is invalid' '
+	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
+	rm -rf "$P" http_child err &&
+
+	git init "$P" &&
+	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
+
+	echo "[submodule \"..\"]" >"$P/.gitmodules" &&
+	echo "path = include/foo" >>"$P/.gitmodules" &&
+	echo "url = git://example.com/git/lib.git" >>"$P/.gitmodules" &&
+	git -C "$P" add .gitmodules &&
+	git -C "$P" commit -m x &&
+
+	configure_exclusion "$P" .gitmodules >h &&
+
+	sane_unset GIT_TEST_SIDEBAND_ALL &&
+	test_must_fail git -c protocol.version=2 -c transfer.fsckobjects=1 \
+		-c fetch.uriprotocols=http,https \
+		clone "$HTTPD_URL/smart/http_parent" http_child 2>err &&
+	test_i18ngrep "disallowed submodule name" err
+'
+
 # DO NOT add non-httpd-specific tests here, because the last part of this
 # test script is only executed when httpd is available and enabled.
 
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index ca62e764b5..cac7f443d0 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -814,53 +814,152 @@ test_expect_success 'set up trailers for next test' '
 	EOF
 '
 
-test_expect_success '%(trailers:unfold) unfolds trailers' '
-	{
-		unfold <trailers
-		echo
-	} >expect &&
-	git for-each-ref --format="%(trailers:unfold)" refs/heads/main >actual &&
-	test_cmp expect actual &&
-	git for-each-ref --format="%(contents:trailers:unfold)" refs/heads/main >actual &&
-	test_cmp expect actual
-'
+test_trailer_option () {
+	title=$1 option=$2
+	cat >expect
+	test_expect_success "$title" '
+		git for-each-ref --format="%($option)" refs/heads/main >actual &&
+		test_cmp expect actual &&
+		git for-each-ref --format="%(contents:$option)" refs/heads/main >actual &&
+		test_cmp expect actual
+	'
+}
 
-test_expect_success '%(trailers:only) shows only "key: value" trailers' '
-	{
-		grep -v patch.description <trailers &&
-		echo
-	} >expect &&
-	git for-each-ref --format="%(trailers:only)" refs/heads/main >actual &&
-	test_cmp expect actual &&
-	git for-each-ref --format="%(contents:trailers:only)" refs/heads/main >actual &&
-	test_cmp expect actual
-'
+test_trailer_option '%(trailers:unfold) unfolds trailers' \
+	'trailers:unfold' <<-EOF
+	$(unfold <trailers)
 
-test_expect_success '%(trailers:only) and %(trailers:unfold) work together' '
-	{
-		grep -v patch.description <trailers | unfold &&
-		echo
-	} >expect &&
-	git for-each-ref --format="%(trailers:only,unfold)" refs/heads/main >actual &&
-	test_cmp expect actual &&
-	git for-each-ref --format="%(trailers:unfold,only)" refs/heads/main >actual &&
-	test_cmp actual actual &&
-	git for-each-ref --format="%(contents:trailers:only,unfold)" refs/heads/main >actual &&
-	test_cmp expect actual &&
-	git for-each-ref --format="%(contents:trailers:unfold,only)" refs/heads/main >actual &&
-	test_cmp actual actual
-'
-
-test_expect_success '%(trailers) rejects unknown trailers arguments' '
-	# error message cannot be checked under i18n
-	cat >expect <<-EOF &&
+	EOF
+
+test_trailer_option '%(trailers:only) shows only "key: value" trailers' \
+	'trailers:only' <<-EOF
+	$(grep -v patch.description <trailers)
+
+	EOF
+
+test_trailer_option '%(trailers:only=no,only=true) shows only "key: value" trailers' \
+	'trailers:only=no,only=true' <<-EOF
+	$(grep -v patch.description <trailers)
+
+	EOF
+
+test_trailer_option '%(trailers:only=yes) shows only "key: value" trailers' \
+	'trailers:only=yes' <<-EOF
+	$(grep -v patch.description <trailers)
+
+	EOF
+
+test_trailer_option '%(trailers:only=no) shows all trailers' \
+	'trailers:only=no' <<-EOF
+	$(cat trailers)
+
+	EOF
+
+test_trailer_option '%(trailers:only) and %(trailers:unfold) work together' \
+	'trailers:only,unfold' <<-EOF
+	$(grep -v patch.description <trailers | unfold)
+
+	EOF
+
+test_trailer_option '%(trailers:unfold) and %(trailers:only) work together' \
+	'trailers:unfold,only' <<-EOF
+	$(grep -v patch.description <trailers | unfold)
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo) shows that trailer' \
+	'trailers:key=Signed-off-by' <<-EOF
+	Signed-off-by: A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo) is case insensitive' \
+	'trailers:key=SiGned-oFf-bY' <<-EOF
+	Signed-off-by: A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo:) trailing colon also works' \
+	'trailers:key=Signed-off-by:' <<-EOF
+	Signed-off-by: A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo) multiple keys' \
+	'trailers:key=Reviewed-by:,key=Signed-off-by' <<-EOF
+	Reviewed-by: A U Thor <author@example.com>
+	Signed-off-by: A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:key=nonexistent) becomes empty' \
+	'trailers:key=Shined-off-by:' <<-EOF
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo) handles multiple lines even if folded' \
+	'trailers:key=Acked-by' <<-EOF
+	$(grep -v patch.description <trailers | grep -v Signed-off-by | grep -v Reviewed-by)
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo,unfold) properly unfolds' \
+	'trailers:key=Signed-Off-by,unfold' <<-EOF
+	$(unfold <trailers | grep Signed-off-by)
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo,only=no) also includes nontrailer lines' \
+	'trailers:key=Signed-off-by,only=no' <<-EOF
+	Signed-off-by: A U Thor <author@example.com>
+	$(grep patch.description <trailers)
+
+	EOF
+
+test_trailer_option '%(trailers:key=foo,valueonly) shows only value' \
+	'trailers:key=Signed-off-by,valueonly' <<-EOF
+	A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:separator) changes separator' \
+	'trailers:separator=%x2C,key=Reviewed-by,key=Signed-off-by:' <<-EOF
+	Reviewed-by: A U Thor <author@example.com>,Signed-off-by: A U Thor <author@example.com>
+	EOF
+
+test_trailer_option '%(trailers:key_value_separator) changes key-value separator' \
+	'trailers:key_value_separator=%x2C,key=Reviewed-by,key=Signed-off-by:' <<-EOF
+	Reviewed-by,A U Thor <author@example.com>
+	Signed-off-by,A U Thor <author@example.com>
+
+	EOF
+
+test_trailer_option '%(trailers:separator,key_value_separator) changes both separators' \
+	'trailers:separator=%x2C,key_value_separator=%x2C,key=Reviewed-by,key=Signed-off-by:' <<-EOF
+	Reviewed-by,A U Thor <author@example.com>,Signed-off-by,A U Thor <author@example.com>
+	EOF
+
+test_failing_trailer_option () {
+	title=$1 option=$2
+	cat >expect
+	test_expect_success "$title" '
+		# error message cannot be checked under i18n
+		test_must_fail git for-each-ref --format="%($option)" refs/heads/main 2>actual &&
+		test_i18ncmp expect actual &&
+		test_must_fail git for-each-ref --format="%(contents:$option)" refs/heads/main 2>actual &&
+		test_i18ncmp expect actual
+	'
+}
+
+test_failing_trailer_option '%(trailers) rejects unknown trailers arguments' \
+	'trailers:unsupported' <<-\EOF
 	fatal: unknown %(trailers) argument: unsupported
 	EOF
-	test_must_fail git for-each-ref --format="%(trailers:unsupported)" 2>actual &&
-	test_i18ncmp expect actual &&
-	test_must_fail git for-each-ref --format="%(contents:trailers:unsupported)" 2>actual &&
-	test_i18ncmp expect actual
-'
+
+test_failing_trailer_option '%(trailers:key) without value is error' \
+	'trailers:key' <<-\EOF
+	fatal: expected %(trailers:key=<value>)
+	EOF
 
 test_expect_success 'if arguments, %(contents:trailers) shows error if colon is missing' '
 	cat >expect <<-EOF &&
diff --git a/t/t7001-mv.sh b/t/t7001-mv.sh
index 080a653083..25bb9bbb89 100755
--- a/t/t7001-mv.sh
+++ b/t/t7001-mv.sh
@@ -3,74 +3,74 @@
 test_description='git mv in subdirs'
 . ./test-lib.sh
 
-test_expect_success \
-    'prepare reference tree' \
-    'mkdir path0 path1 &&
-     cp "$TEST_DIRECTORY"/../COPYING path0/COPYING &&
-     git add path0/COPYING &&
-     git commit -m add -a'
+test_expect_success 'prepare reference tree' '
+	mkdir path0 path1 &&
+	cp "$TEST_DIRECTORY"/../COPYING path0/COPYING &&
+	git add path0/COPYING &&
+	git commit -m add -a
+'
 
-test_expect_success \
-    'moving the file out of subdirectory' \
-    'cd path0 && git mv COPYING ../path1/COPYING'
+test_expect_success 'moving the file out of subdirectory' '
+	git -C path0 mv COPYING ../path1/COPYING
+'
 
 # in path0 currently
-test_expect_success \
-    'commiting the change' \
-    'cd .. && git commit -m move-out -a'
+test_expect_success 'commiting the change' '
+	git commit -m move-out -a
+'
 
-test_expect_success \
-    'checking the commit' \
-    'git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
-    grep "^R100..*path0/COPYING..*path1/COPYING" actual'
+test_expect_success 'checking the commit' '
+	git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
+	grep "^R100..*path0/COPYING..*path1/COPYING" actual
+'
 
-test_expect_success \
-    'moving the file back into subdirectory' \
-    'cd path0 && git mv ../path1/COPYING COPYING'
+test_expect_success 'moving the file back into subdirectory' '
+	git -C path0 mv ../path1/COPYING COPYING
+'
 
 # in path0 currently
-test_expect_success \
-    'commiting the change' \
-    'cd .. && git commit -m move-in -a'
-
-test_expect_success \
-    'checking the commit' \
-    'git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
-    grep "^R100..*path1/COPYING..*path0/COPYING" actual'
-
-test_expect_success \
-    'mv --dry-run does not move file' \
-    'git mv -n path0/COPYING MOVED &&
-     test -f path0/COPYING &&
-     test ! -f MOVED'
-
-test_expect_success \
-    'checking -k on non-existing file' \
-    'git mv -k idontexist path0'
-
-test_expect_success \
-    'checking -k on untracked file' \
-    'touch untracked1 &&
-     git mv -k untracked1 path0 &&
-     test -f untracked1 &&
-     test ! -f path0/untracked1'
-
-test_expect_success \
-    'checking -k on multiple untracked files' \
-    'touch untracked2 &&
-     git mv -k untracked1 untracked2 path0 &&
-     test -f untracked1 &&
-     test -f untracked2 &&
-     test ! -f path0/untracked1 &&
-     test ! -f path0/untracked2'
-
-test_expect_success \
-    'checking -f on untracked file with existing target' \
-    'touch path0/untracked1 &&
-     test_must_fail git mv -f untracked1 path0 &&
-     test ! -f .git/index.lock &&
-     test -f untracked1 &&
-     test -f path0/untracked1'
+test_expect_success 'commiting the change' '
+	git commit -m move-in -a
+'
+
+test_expect_success 'checking the commit' '
+	git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
+	grep "^R100..*path1/COPYING..*path0/COPYING" actual
+'
+
+test_expect_success 'mv --dry-run does not move file' '
+	git mv -n path0/COPYING MOVED &&
+	test -f path0/COPYING &&
+	test ! -f MOVED
+'
+
+test_expect_success 'checking -k on non-existing file' '
+	git mv -k idontexist path0
+'
+
+test_expect_success 'checking -k on untracked file' '
+	>untracked1 &&
+	git mv -k untracked1 path0 &&
+	test -f untracked1 &&
+	test ! -f path0/untracked1
+'
+
+test_expect_success 'checking -k on multiple untracked files' '
+	>untracked2 &&
+	git mv -k untracked1 untracked2 path0 &&
+	test -f untracked1 &&
+	test -f untracked2 &&
+	test ! -f path0/untracked1 &&
+	test ! -f path0/untracked2
+'
+
+test_expect_success 'checking -f on untracked file with existing target' '
+	>path0/untracked1 &&
+	test_must_fail git mv -f untracked1 path0 &&
+	test ! -f .git/index.lock &&
+	test -f untracked1 &&
+	test -f path0/untracked1
+'
 
 # clean up the mess in case bad things happen
 rm -f idontexist untracked1 untracked2 \
@@ -78,87 +78,89 @@ rm -f idontexist untracked1 untracked2 \
      .git/index.lock
 rmdir path1
 
-test_expect_success \
-    'moving to absent target with trailing slash' \
-    'test_must_fail git mv path0/COPYING no-such-dir/ &&
-     test_must_fail git mv path0/COPYING no-such-dir// &&
-     git mv path0/ no-such-dir/ &&
-     test_path_is_dir no-such-dir'
-
-test_expect_success \
-    'clean up' \
-    'git reset --hard'
-
-test_expect_success \
-    'moving to existing untracked target with trailing slash' \
-    'mkdir path1 &&
-     git mv path0/ path1/ &&
-     test_path_is_dir path1/path0/'
-
-test_expect_success \
-    'moving to existing tracked target with trailing slash' \
-    'mkdir path2 &&
-     >path2/file && git add path2/file &&
-     git mv path1/path0/ path2/ &&
-     test_path_is_dir path2/path0/'
-
-test_expect_success \
-    'clean up' \
-    'git reset --hard'
-
-test_expect_success \
-    'adding another file' \
-    'cp "$TEST_DIRECTORY"/../README.md path0/README &&
-     git add path0/README &&
-     git commit -m add2 -a'
-
-test_expect_success \
-    'moving whole subdirectory' \
-    'git mv path0 path2'
-
-test_expect_success \
-    'commiting the change' \
-    'git commit -m dir-move -a'
-
-test_expect_success \
-    'checking the commit' \
-    'git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
-     grep "^R100..*path0/COPYING..*path2/COPYING" actual &&
-     grep "^R100..*path0/README..*path2/README" actual'
-
-test_expect_success \
-    'succeed when source is a prefix of destination' \
-    'git mv path2/COPYING path2/COPYING-renamed'
-
-test_expect_success \
-    'moving whole subdirectory into subdirectory' \
-    'git mv path2 path1'
-
-test_expect_success \
-    'commiting the change' \
-    'git commit -m dir-move -a'
-
-test_expect_success \
-    'checking the commit' \
-    'git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
-     grep "^R100..*path2/COPYING..*path1/path2/COPYING" actual &&
-     grep "^R100..*path2/README..*path1/path2/README" actual'
-
-test_expect_success \
-    'do not move directory over existing directory' \
-    'mkdir path0 && mkdir path0/path2 && test_must_fail git mv path2 path0'
-
-test_expect_success \
-    'move into "."' \
-    'git mv path1/path2/ .'
+test_expect_success 'moving to absent target with trailing slash' '
+	test_must_fail git mv path0/COPYING no-such-dir/ &&
+	test_must_fail git mv path0/COPYING no-such-dir// &&
+	git mv path0/ no-such-dir/ &&
+	test_path_is_dir no-such-dir
+'
+
+test_expect_success 'clean up' '
+	git reset --hard
+'
+
+test_expect_success 'moving to existing untracked target with trailing slash' '
+	mkdir path1 &&
+	git mv path0/ path1/ &&
+	test_path_is_dir path1/path0/
+'
+
+test_expect_success 'moving to existing tracked target with trailing slash' '
+	mkdir path2 &&
+	>path2/file && git add path2/file &&
+	git mv path1/path0/ path2/ &&
+	test_path_is_dir path2/path0/
+'
+
+test_expect_success 'clean up' '
+	git reset --hard
+'
+
+test_expect_success 'adding another file' '
+	cp "$TEST_DIRECTORY"/../README.md path0/README &&
+	git add path0/README &&
+	git commit -m add2 -a
+'
+
+test_expect_success 'moving whole subdirectory' '
+	git mv path0 path2
+'
+
+test_expect_success 'commiting the change' '
+	git commit -m dir-move -a
+'
+
+test_expect_success 'checking the commit' '
+	git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
+	grep "^R100..*path0/COPYING..*path2/COPYING" actual &&
+	grep "^R100..*path0/README..*path2/README" actual
+'
+
+test_expect_success 'succeed when source is a prefix of destination' '
+	git mv path2/COPYING path2/COPYING-renamed
+'
+
+test_expect_success 'moving whole subdirectory into subdirectory' '
+	git mv path2 path1
+'
+
+test_expect_success 'commiting the change' '
+	git commit -m dir-move -a
+'
+
+test_expect_success 'checking the commit' '
+	git diff-tree -r -M --name-status  HEAD^ HEAD >actual &&
+	grep "^R100..*path2/COPYING..*path1/path2/COPYING" actual &&
+	grep "^R100..*path2/README..*path1/path2/README" actual
+'
+
+test_expect_success 'do not move directory over existing directory' '
+	mkdir path0 &&
+	mkdir path0/path2 &&
+	test_must_fail git mv path2 path0
+'
+
+test_expect_success 'move into "."' '
+	git mv path1/path2/ .
+'
 
 test_expect_success "Michael Cassar's test case" '
 	rm -fr .git papers partA &&
 	git init &&
 	mkdir -p papers/unsorted papers/all-papers partA &&
-	echo a > papers/unsorted/Thesis.pdf &&
-	echo b > partA/outline.txt &&
-	echo c > papers/unsorted/_another &&
+	echo a >papers/unsorted/Thesis.pdf &&
+	echo b >partA/outline.txt &&
+	echo c >papers/unsorted/_another &&
 	git add papers partA &&
 	T1=$(git write-tree) &&
 
@@ -181,43 +183,42 @@ test_expect_success "Sergey Vlasov's test case" '
 	git mv ab a
 '
 
-test_expect_success 'absolute pathname' '(
-
-	rm -fr mine &&
-	mkdir mine &&
-	cd mine &&
-	test_create_repo one &&
-	cd one &&
-	mkdir sub &&
-	>sub/file &&
-	git add sub/file &&
-
-	git mv sub "$(pwd)/in" &&
-	! test -d sub &&
-	test -d in &&
-	git ls-files --error-unmatch in/file
-
-
-)'
-
-test_expect_success 'absolute pathname outside should fail' '(
-
-	rm -fr mine &&
-	mkdir mine &&
-	cd mine &&
-	out=$(pwd) &&
-	test_create_repo one &&
-	cd one &&
-	mkdir sub &&
-	>sub/file &&
-	git add sub/file &&
-
-	test_must_fail git mv sub "$out/out" &&
-	test -d sub &&
-	! test -d ../in &&
-	git ls-files --error-unmatch sub/file
+test_expect_success 'absolute pathname' '
+	(
+		rm -fr mine &&
+		mkdir mine &&
+		cd mine &&
+		test_create_repo one &&
+		cd one &&
+		mkdir sub &&
+		>sub/file &&
+		git add sub/file &&
+
+		git mv sub "$(pwd)/in" &&
+		! test -d sub &&
+		test -d in &&
+		git ls-files --error-unmatch in/file
+	)
+'
 
-)'
+test_expect_success 'absolute pathname outside should fail' '
+	(
+		rm -fr mine &&
+		mkdir mine &&
+		cd mine &&
+		out=$(pwd) &&
+		test_create_repo one &&
+		cd one &&
+		mkdir sub &&
+		>sub/file &&
+		git add sub/file &&
+
+		test_must_fail git mv sub "$out/out" &&
+		test -d sub &&
+		! test -d ../in &&
+		git ls-files --error-unmatch sub/file
+	)
+'
 
 test_expect_success 'git mv to move multiple sources into a directory' '
 	rm -fr .git && git init &&
@@ -227,23 +228,24 @@ test_expect_success 'git mv to move multiple sources into a directory' '
 	git add dir/?.txt &&
 	git mv dir/a.txt dir/b.txt other &&
 	git ls-files >actual &&
-	{ echo other/a.txt; echo other/b.txt; } >expect &&
+	cat >expect <<-\EOF &&
+	other/a.txt
+	other/b.txt
+	EOF
 	test_cmp expect actual
 '
 
 test_expect_success 'git mv should not change sha1 of moved cache entry' '
-
 	rm -fr .git &&
 	git init &&
 	echo 1 >dirty &&
 	git add dirty &&
 	entry="$(git ls-files --stage dirty | cut -f 1)" &&
 	git mv dirty dirty2 &&
-	[ "$entry" = "$(git ls-files --stage dirty2 | cut -f 1)" ] &&
+	test "$entry" = "$(git ls-files --stage dirty2 | cut -f 1)" &&
 	echo 2 >dirty2 &&
 	git mv dirty2 dirty &&
-	[ "$entry" = "$(git ls-files --stage dirty | cut -f 1)" ]
-
+	test "$entry" = "$(git ls-files --stage dirty | cut -f 1)"
 '
 
 rm -f dirty dirty2
@@ -266,7 +268,6 @@ test_expect_success 'git mv error on conflicted file' '
 '
 
 test_expect_success 'git mv should overwrite symlink to a file' '
-
 	rm -fr .git &&
 	git init &&
 	echo 1 >moved &&
@@ -279,13 +280,11 @@ test_expect_success 'git mv should overwrite symlink to a file' '
 	test "$(cat symlink)" = 1 &&
 	git update-index --refresh &&
 	git diff-files --quiet
-
 '
 
 rm -f moved symlink
 
 test_expect_success 'git mv should overwrite file with a symlink' '
-
 	rm -fr .git &&
 	git init &&
 	echo 1 >moved &&
@@ -296,11 +295,9 @@ test_expect_success 'git mv should overwrite file with a symlink' '
 	! test -e symlink &&
 	git update-index --refresh &&
 	git diff-files --quiet
-
 '
 
 test_expect_success SYMLINKS 'check moved symlink' '
-
 	test -h moved
 '
 
@@ -335,11 +332,8 @@ test_expect_success 'git mv moves a submodule with a .git directory and no .gitm
 	mkdir mod &&
 	git mv sub mod/sub &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	git update-index --refresh &&
 	git diff-files --quiet
 '
@@ -358,11 +352,8 @@ test_expect_success 'git mv moves a submodule with a .git directory and .gitmodu
 	mkdir mod &&
 	git mv sub mod/sub &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	echo mod/sub >expected &&
 	git config -f .gitmodules submodule.sub.path >actual &&
 	test_cmp expected actual &&
@@ -376,16 +367,10 @@ test_expect_success 'git mv moves a submodule with gitfile' '
 	git submodule update &&
 	entry="$(git ls-files --stage sub | cut -f 1)" &&
 	mkdir mod &&
-	(
-		cd mod &&
-		git mv ../sub/ .
-	) &&
+	git -C mod mv ../sub/ . &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	echo mod/sub >expected &&
 	git config -f .gitmodules submodule.sub.path >actual &&
 	test_cmp expected actual &&
@@ -403,11 +388,8 @@ test_expect_success 'mv does not complain when no .gitmodules file is found' '
 	git mv sub mod/sub 2>actual.err &&
 	test_must_be_empty actual.err &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	git update-index --refresh &&
 	git diff-files --quiet
 '
@@ -427,11 +409,8 @@ test_expect_success 'mv will error out on a modified .gitmodules file unless sta
 	git mv sub mod/sub 2>actual.err &&
 	test_must_be_empty actual.err &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	git update-index --refresh &&
 	git diff-files --quiet
 '
@@ -448,11 +427,8 @@ test_expect_success 'mv issues a warning when section is not found in .gitmodule
 	git mv sub mod/sub 2>actual.err &&
 	test_cmp expect.err actual.err &&
 	! test -e sub &&
-	[ "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" ] &&
-	(
-		cd mod/sub &&
-		git status
-	) &&
+	test "$entry" = "$(git ls-files --stage mod/sub | cut -f 1)" &&
+	git -C mod/sub status &&
 	git update-index --refresh &&
 	git diff-files --quiet
 '
@@ -515,15 +491,17 @@ test_expect_success 'moving a submodule in nested directories' '
 test_expect_success 'moving nested submodules' '
 	git commit -am "cleanup commit" &&
 	mkdir sub_nested_nested &&
-	(cd sub_nested_nested &&
-		touch nested_level2 &&
+	(
+		cd sub_nested_nested &&
+		>nested_level2 &&
 		git init &&
 		git add . &&
 		git commit -m "nested level 2"
 	) &&
 	mkdir sub_nested &&
-	(cd sub_nested &&
-		touch nested_level1 &&
+	(
+		cd sub_nested &&
+		>nested_level1 &&
 		git init &&
 		git add . &&
 		git commit -m "nested level 1" &&