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author | Taylor Blau <me@ttaylorr.com> | 2021-03-30 15:04:26 (GMT) |
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committer | Junio C Hamano <gitster@pobox.com> | 2021-04-01 20:07:37 (GMT) |
commit | f894081deae88e875536bd53c56b8b189474770c (patch) | |
tree | 4e0b90800abc74c0164aff8abb883a1dffbf7262 /midx.c | |
parent | b25fd24c00a6670a940d998287736c5abe4ce09d (diff) | |
download | git-f894081deae88e875536bd53c56b8b189474770c.zip git-f894081deae88e875536bd53c56b8b189474770c.tar.gz git-f894081deae88e875536bd53c56b8b189474770c.tar.bz2 |
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 'midx.c')
-rw-r--r-- | midx.c | 11 |
1 files changed, 11 insertions, 0 deletions
@@ -47,11 +47,22 @@ static uint8_t oid_version(void) } } +static const unsigned char *get_midx_checksum(struct multi_pack_index *m) +{ + return m->data + m->data_len - the_hash_algo->rawsz; +} + static char *get_midx_filename(const char *object_dir) { return xstrfmt("%s/pack/multi-pack-index", object_dir); } +char *get_midx_rev_filename(struct multi_pack_index *m) +{ + return xstrfmt("%s/pack/multi-pack-index-%s.rev", + m->object_dir, hash_to_hex(get_midx_checksum(m))); +} + static int midx_read_oid_fanout(const unsigned char *chunk_start, size_t chunk_size, void *data) { |