diff options
author | Taylor Blau <me@ttaylorr.com> | 2021-03-30 18:04:26 +0300 |
---|---|---|
committer | Junio C Hamano <gitster@pobox.com> | 2021-04-01 23:07:37 +0300 |
commit | f894081deae88e875536bd53c56b8b189474770c (patch) | |
tree | 4e0b90800abc74c0164aff8abb883a1dffbf7262 /pack-revindex.h | |
parent | b25fd24c00a6670a940d998287736c5abe4ce09d (diff) |
pack-revindex: read multi-pack reverse indexes
Implement reading for multi-pack reverse indexes, as described in the
previous patch.
Note that these functions don't yet have any callers, and won't until
multi-pack reachability bitmaps are introduced in a later patch series.
In the meantime, this patch implements some of the infrastructure
necessary to support multi-pack bitmaps.
There are three new functions exposed by the revindex API:
- load_midx_revindex(): loads the reverse index corresponding to the
given multi-pack index.
- midx_to_pack_pos() and pack_pos_to_midx(): these convert between the
multi-pack index and pseudo-pack order.
load_midx_revindex() and pack_pos_to_midx() are both relatively
straightforward.
load_midx_revindex() needs a few functions to be exposed from the midx
API. One to get the checksum of a midx, and another to get the .rev's
filename. Similar to recent changes in the packed_git struct, three new
fields are added to the multi_pack_index struct: one to keep track of
the size, one to keep track of the mmap'd pointer, and another to point
past the header and at the reverse index's data.
pack_pos_to_midx() simply reads the corresponding entry out of the
table.
midx_to_pack_pos() is the trickiest, since it needs to find an object's
position in the psuedo-pack order, but that order can only be recovered
in the .rev file itself. This mapping can be implemented with a binary
search, but note that the thing we're binary searching over isn't an
array of values, but rather a permuted order of those values.
So, when comparing two items, it's helpful to keep in mind the
difference. Instead of a traditional binary search, where you are
comparing two things directly, here we're comparing a (pack, offset)
tuple with an index into the multi-pack index. That index describes
another (pack, offset) tuple, and it is _those_ two tuples that are
compared.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'pack-revindex.h')
-rw-r--r-- | pack-revindex.h | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/pack-revindex.h b/pack-revindex.h index ba7c82c125..479b8f2f9c 100644 --- a/pack-revindex.h +++ b/pack-revindex.h @@ -14,6 +14,20 @@ * * - offset: the byte offset within the .pack file at which the object contents * can be found + * + * The revindex can also be used with a multi-pack index (MIDX). In this + * setting: + * + * - index position refers to an object's numeric position within the MIDX + * + * - pack position refers to an object's position within a non-existent pack + * described by the MIDX. The pack structure is described in + * Documentation/technical/pack-format.txt. + * + * It is effectively a concatanation of all packs in the MIDX (ordered by + * their numeric ID within the MIDX) in their original order within each + * pack), removing duplicates, and placing the preferred pack (if any) + * first. */ @@ -24,6 +38,7 @@ #define GIT_TEST_REV_INDEX_DIE_IN_MEMORY "GIT_TEST_REV_INDEX_DIE_IN_MEMORY" struct packed_git; +struct multi_pack_index; /* * load_pack_revindex populates the revindex's internal data-structures for the @@ -35,6 +50,22 @@ struct packed_git; int load_pack_revindex(struct packed_git *p); /* + * load_midx_revindex loads the '.rev' file corresponding to the given + * multi-pack index by mmap-ing it and assigning pointers in the + * multi_pack_index to point at it. + * + * A negative number is returned on error. + */ +int load_midx_revindex(struct multi_pack_index *m); + +/* + * Frees resources associated with a multi-pack reverse index. + * + * A negative number is returned on error. + */ +int close_midx_revindex(struct multi_pack_index *m); + +/* * offset_to_pack_pos converts an object offset to a pack position. This * function returns zero on success, and a negative number otherwise. The * parameter 'pos' is usable only on success. @@ -71,4 +102,26 @@ uint32_t pack_pos_to_index(struct packed_git *p, uint32_t pos); */ off_t pack_pos_to_offset(struct packed_git *p, uint32_t pos); +/* + * pack_pos_to_midx converts the object at position "pos" within the MIDX + * pseudo-pack into a MIDX position. + * + * If the reverse index has not yet been loaded, or the position is out of + * bounds, this function aborts. + * + * This function runs in time O(log N) with the number of objects in the MIDX. + */ +uint32_t pack_pos_to_midx(struct multi_pack_index *m, uint32_t pos); + +/* + * midx_to_pack_pos converts from the MIDX-relative position at "at" to the + * corresponding pack position. + * + * If the reverse index has not yet been loaded, or the position is out of + * bounds, this function aborts. + * + * This function runs in constant time. + */ +int midx_to_pack_pos(struct multi_pack_index *midx, uint32_t at, uint32_t *pos); + #endif |