From 3b7a4475b0912d6d78c5e2354599dbc8f1ade479 Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Sun, 26 Mar 2023 22:45:41 +0000 Subject: split-index; stop abusing the `base_oid` to strip the "link" extension When a split-index is in effect, the `$GIT_DIR/index` file needs to contain a "link" extension that contains all the information about the split-index, including the information about the shared index. However, in some cases Git needs to suppress writing that "link" extension (i.e. to fall back to writing a full index) even if the in-memory index structure _has_ a `split_index` configured. This is the case e.g. when "too many not shared" index entries exist. In such instances, the current code sets the `base_oid` field of said `split_index` structure to all-zero to indicate that `do_write_index()` should skip writing the "link" extension. This can lead to problems later on, when the in-memory index is still used to perform other operations and eventually wants to write a split-index, detects the presence of the `split_index` and reuses that, too (under the assumption that it has been initialized correctly and still has a non-null `base_oid`). Let's stop zeroing out the `base_oid` to indicate that the "link" extension should not be written. One might be tempted to simply call `discard_split_index()` instead, under the assumption that Git decided to write a non-split index and therefore the `split_index` structure might no longer be wanted. However, that is not possible because that would release index entries in `split_index->base` that are likely to still be in use. Therefore we cannot do that. The next best thing we _can_ do is to introduce a bit field to indicate specifically which index extensions (not) to write. So that's what we do here. Signed-off-by: Johannes Schindelin Signed-off-by: Junio C Hamano --- read-cache.c | 49 ++++++++++++++++++++++++++++++++----------------- 1 file changed, 32 insertions(+), 17 deletions(-) (limited to 'read-cache.c') diff --git a/read-cache.c b/read-cache.c index b09128b188..7c9a0eeeac 100644 --- a/read-cache.c +++ b/read-cache.c @@ -2868,6 +2868,16 @@ static int record_ieot(void) return !git_config_get_index_threads(&val) && val != 1; } +enum write_extensions { + WRITE_NO_EXTENSION = 0, + WRITE_SPLIT_INDEX_EXTENSION = 1<<0, + WRITE_CACHE_TREE_EXTENSION = 1<<1, + WRITE_RESOLVE_UNDO_EXTENSION = 1<<2, + WRITE_UNTRACKED_CACHE_EXTENSION = 1<<3, + WRITE_FSMONITOR_EXTENSION = 1<<4, +}; +#define WRITE_ALL_EXTENSIONS ((enum write_extensions)-1) + /* * On success, `tempfile` is closed. If it is the temporary file * of a `struct lock_file`, we will therefore effectively perform @@ -2876,7 +2886,7 @@ static int record_ieot(void) * rely on it. */ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, - int strip_extensions, unsigned flags) + enum write_extensions write_extensions, unsigned flags) { uint64_t start = getnanotime(); struct hashfile *f; @@ -3045,8 +3055,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, return -1; } - if (!strip_extensions && istate->split_index && - !is_null_oid(&istate->split_index->base_oid)) { + if (write_extensions & WRITE_SPLIT_INDEX_EXTENSION && + istate->split_index) { struct strbuf sb = STRBUF_INIT; if (istate->sparse_index) @@ -3060,7 +3070,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, if (err) return -1; } - if (!strip_extensions && !drop_cache_tree && istate->cache_tree) { + if (write_extensions & WRITE_CACHE_TREE_EXTENSION && + !drop_cache_tree && istate->cache_tree) { struct strbuf sb = STRBUF_INIT; cache_tree_write(&sb, istate->cache_tree); @@ -3070,7 +3081,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, if (err) return -1; } - if (!strip_extensions && istate->resolve_undo) { + if (write_extensions & WRITE_RESOLVE_UNDO_EXTENSION && + istate->resolve_undo) { struct strbuf sb = STRBUF_INIT; resolve_undo_write(&sb, istate->resolve_undo); @@ -3081,7 +3093,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, if (err) return -1; } - if (!strip_extensions && istate->untracked) { + if (write_extensions & WRITE_UNTRACKED_CACHE_EXTENSION && + istate->untracked) { struct strbuf sb = STRBUF_INIT; write_untracked_extension(&sb, istate->untracked); @@ -3092,7 +3105,8 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile, if (err) return -1; } - if (!strip_extensions && istate->fsmonitor_last_update) { + if (write_extensions & WRITE_FSMONITOR_EXTENSION && + istate->fsmonitor_last_update) { struct strbuf sb = STRBUF_INIT; write_fsmonitor_extension(&sb, istate); @@ -3166,8 +3180,10 @@ static int commit_locked_index(struct lock_file *lk) return commit_lock_file(lk); } -static int do_write_locked_index(struct index_state *istate, struct lock_file *lock, - unsigned flags) +static int do_write_locked_index(struct index_state *istate, + struct lock_file *lock, + unsigned flags, + enum write_extensions write_extensions) { int ret; int was_full = istate->sparse_index == INDEX_EXPANDED; @@ -3185,7 +3201,7 @@ static int do_write_locked_index(struct index_state *istate, struct lock_file *l */ trace2_region_enter_printf("index", "do_write_index", the_repository, "%s", get_lock_file_path(lock)); - ret = do_write_index(istate, lock->tempfile, 0, flags); + ret = do_write_index(istate, lock->tempfile, write_extensions, flags); trace2_region_leave_printf("index", "do_write_index", the_repository, "%s", get_lock_file_path(lock)); @@ -3214,7 +3230,7 @@ static int write_split_index(struct index_state *istate, { int ret; prepare_to_write_split_index(istate); - ret = do_write_locked_index(istate, lock, flags); + ret = do_write_locked_index(istate, lock, flags, WRITE_ALL_EXTENSIONS); finish_writing_split_index(istate); return ret; } @@ -3289,7 +3305,7 @@ static int write_shared_index(struct index_state *istate, trace2_region_enter_printf("index", "shared/do_write_index", the_repository, "%s", get_tempfile_path(*temp)); - ret = do_write_index(si->base, *temp, 1, flags); + ret = do_write_index(si->base, *temp, WRITE_NO_EXTENSION, flags); trace2_region_leave_printf("index", "shared/do_write_index", the_repository, "%s", get_tempfile_path(*temp)); @@ -3366,9 +3382,8 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock, if ((!si && !test_split_index_env) || alternate_index_output || (istate->cache_changed & ~EXTMASK)) { - if (si) - oidclr(&si->base_oid); - ret = do_write_locked_index(istate, lock, flags); + ret = do_write_locked_index(istate, lock, flags, + ~WRITE_SPLIT_INDEX_EXTENSION); goto out; } @@ -3394,8 +3409,8 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock, /* Same initial permissions as the main .git/index file */ temp = mks_tempfile_sm(git_path("sharedindex_XXXXXX"), 0, 0666); if (!temp) { - oidclr(&si->base_oid); - ret = do_write_locked_index(istate, lock, flags); + ret = do_write_locked_index(istate, lock, flags, + ~WRITE_SPLIT_INDEX_EXTENSION); goto out; } ret = write_shared_index(istate, &temp, flags); -- cgit v1.2.3