midx: read `RIDX` chunk when present

When a MIDX contains the new `RIDX` chunk, ensure that the reverse index
is read from it instead of the on-disk .rev file. Since we need to
encode the object order in the MIDX itself for correctness reasons,
there is no point in storing the same data again outside of the MIDX.

So, this patch stops writing separate .rev files, and reads it out of
the MIDX itself. This is possible to do with relatively little new code,
since the format of the RIDX chunk is identical to the data in the .rev
file. In other words, we can implement this by pointing the
`revindex_data` field at the reverse index chunk of the MIDX instead of
the .rev file without any other changes.

Note that we have two knobs that are adjusted for the new tests:
GIT_TEST_MIDX_WRITE_REV and GIT_TEST_MIDX_READ_RIDX. The former controls
whether the MIDX .rev is written at all, and the latter controls whether
we read the MIDX's RIDX chunk.

Both are necessary to ensure that the test added at the beginning of
this series continues to work. This is because we always need to write
the RIDX chunk in the MIDX in order to change its checksum, but we want
to make sure reading the existing .rev file still works (since the RIDX
chunk takes precedence by default).

Arguably this isn't a very interesting mode to test, because the
precedence rules mean that we'll always read the RIDX chunk over the
.rev file. But it makes it impossible for a user to induce corruption in
their repository by adjusting the test knobs (since if we had an
either/or knob they could stop writing the RIDX chunk, allowing them to
tweak the MIDX's object order without changing its checksum).

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/midx.c b/midx.c
index 0248c4577c7241acfb6290d67cd2fe5fce07f228..6e6cb0eb0494f543f4e2ea2e4fd5521950776f09 100644 (file)
--- a/midx.c
+++ b/midx.c
@@ -162,6 +162,9 @@ struct multi_pack_index *load_multi_pack_index(const char *object_dir, int local
 
        pair_chunk(cf, MIDX_CHUNKID_LARGEOFFSETS, &m->chunk_large_offsets);
 
+       if (git_env_bool("GIT_TEST_MIDX_READ_RIDX", 1))
+               pair_chunk(cf, MIDX_CHUNKID_REVINDEX, &m->chunk_revindex);
+
        m->num_objects = ntohl(m->chunk_oid_fanout[255]);
 
        CALLOC_ARRAY(m->pack_names, m->num_packs);
@@ -1429,7 +1432,8 @@ static int write_midx_internal(const char *object_dir,
        finalize_hashfile(f, midx_hash, CSUM_FSYNC | CSUM_HASH_IN_STREAM);
        free_chunkfile(cf);
 
-       if (flags & MIDX_WRITE_REV_INDEX)
+       if (flags & MIDX_WRITE_REV_INDEX &&
+           git_env_bool("GIT_TEST_MIDX_WRITE_REV", 0))
                write_midx_reverse_index(midx_name.buf, midx_hash, &ctx);
        if (flags & MIDX_WRITE_BITMAP) {
                if (write_midx_bitmap(midx_name.buf, midx_hash, &ctx,

diff --git a/midx.h b/midx.h
index b7d79a515c63a73422755737d789b0c2febe22a9..22e8e53288ec226f7673d8a0f277961d5bb1d856 100644 (file)
--- a/midx.h
+++ b/midx.h
@@ -36,6 +36,7 @@ struct multi_pack_index {
        const unsigned char *chunk_oid_lookup;
        const unsigned char *chunk_object_offsets;
        const unsigned char *chunk_large_offsets;
+       const unsigned char *chunk_revindex;
 
        const char **pack_names;
        struct packed_git **packs;

diff --git a/pack-revindex.c b/pack-revindex.c
index bd15ebad03ec024ac85fa5b856e7b2f694e027c9..08dc1601679f1011f7ff38b7a721dbb4dd116c85 100644 (file)
--- a/pack-revindex.c
+++ b/pack-revindex.c
@@ -298,9 +298,26 @@ int load_midx_revindex(struct multi_pack_index *m)
 {
        struct strbuf revindex_name = STRBUF_INIT;
        int ret;
+
        if (m->revindex_data)
                return 0;
 
+       if (m->chunk_revindex) {
+               /*
+                * If the MIDX `m` has a `RIDX` chunk, then use its contents for
+                * the reverse index instead of trying to load a separate `.rev`
+                * file.
+                *
+                * Note that we do *not* set `m->revindex_map` here, since we do
+                * not want to accidentally call munmap() in the middle of the
+                * MIDX.
+                */
+               trace2_data_string("load_midx_revindex", the_repository,
+                                  "source", "midx");
+               m->revindex_data = (const uint32_t *)m->chunk_revindex;
+               return 0;
+       }
+
        trace2_data_string("load_midx_revindex", the_repository,
                           "source", "rev");
 

diff --git a/t/lib-bitmap.sh b/t/lib-bitmap.sh
index 253895c04ed8fb7bcd6fcb20b216eb51327c186a..a95537e759b0365db3f80ccf9135838da0cbde5e 100644 (file)
--- a/t/lib-bitmap.sh
+++ b/t/lib-bitmap.sh
@@ -290,7 +290,7 @@ test_rev_exists () {
 }
 
 midx_bitmap_core () {
-       rev_kind="${1:-rev}"
+       rev_kind="${1:-midx}"
 
        setup_bitmap_history
 
@@ -434,7 +434,7 @@ midx_bitmap_core () {
 }
 
 midx_bitmap_partial_tests () {
-       rev_kind="${1:-rev}"
+       rev_kind="${1:-midx}"
 
        test_expect_success 'setup partial bitmaps' '
                test_commit packed &&

diff --git a/t/t5326-multi-pack-bitmaps.sh b/t/t5326-multi-pack-bitmaps.sh
index 100ac90d154c003e6fda13a5d4a261947083d7ea..c0924074c4de0eddec3ebb8ff9c66484c79483c9 100755 (executable)
--- a/t/t5326-multi-pack-bitmaps.sh
+++ b/t/t5326-multi-pack-bitmaps.sh
@@ -9,6 +9,12 @@ test_description='exercise basic multi-pack bitmap functionality'
 GIT_TEST_MULTI_PACK_INDEX=0
 GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
 
+# This test exercise multi-pack bitmap functionality where the object order is
+# stored and read from a special chunk within the MIDX, so use the default
+# behavior here.
+sane_unset GIT_TEST_MIDX_WRITE_REV
+sane_unset GIT_TEST_MIDX_READ_RIDX
+
 midx_bitmap_core
 
 bitmap_reuse_tests() {

diff --git a/t/t5327-multi-pack-bitmaps-rev.sh b/t/t5327-multi-pack-bitmaps-rev.sh
new file mode 100755 (executable)
index 0000000..d30ba63
--- /dev/null
+++ b/t/t5327-multi-pack-bitmaps-rev.sh
@@ -0,0 +1,23 @@
+#!/bin/sh
+
+test_description='exercise basic multi-pack bitmap functionality (.rev files)'
+
+. ./test-lib.sh
+. "${TEST_DIRECTORY}/lib-bitmap.sh"
+
+# We'll be writing our own midx and bitmaps, so avoid getting confused by the
+# automatic ones.
+GIT_TEST_MULTI_PACK_INDEX=0
+GIT_TEST_MULTI_PACK_INDEX_WRITE_BITMAP=0
+
+# Unlike t5326, this test exercise multi-pack bitmap functionality where the
+# object order is stored in a separate .rev file.
+GIT_TEST_MIDX_WRITE_REV=1
+GIT_TEST_MIDX_READ_RIDX=0
+export GIT_TEST_MIDX_WRITE_REV
+export GIT_TEST_MIDX_READ_RIDX
+
+midx_bitmap_core rev
+midx_bitmap_partial_tests rev
+
+test_done

diff --git a/t/t7700-repack.sh b/t/t7700-repack.sh
index 4693f8dc2bb9d5182649af7b1cadba26750a1c03..02a6633a165b34d169e9cad2583fa18347bff723 100755 (executable)
--- a/t/t7700-repack.sh
+++ b/t/t7700-repack.sh
@@ -311,16 +311,13 @@ test_expect_success 'cleans up MIDX when appropriate' '
                checksum=$(midx_checksum $objdir) &&
                test_path_is_file $midx &&
                test_path_is_file $midx-$checksum.bitmap &&
-               test_path_is_file $midx-$checksum.rev &&
 
                test_commit repack-3 &&
                GIT_TEST_MULTI_PACK_INDEX=0 git repack -Adb --write-midx &&
 
                test_path_is_file $midx &&
                test_path_is_missing $midx-$checksum.bitmap &&
-               test_path_is_missing $midx-$checksum.rev &&
                test_path_is_file $midx-$(midx_checksum $objdir).bitmap &&
-               test_path_is_file $midx-$(midx_checksum $objdir).rev &&
 
                test_commit repack-4 &&
                GIT_TEST_MULTI_PACK_INDEX=0 git repack -Adb &&
@@ -353,7 +350,6 @@ test_expect_success '--write-midx with preferred bitmap tips' '
                test_line_count = 1 before &&
 
                rm -fr $midx-$(midx_checksum $objdir).bitmap &&
-               rm -fr $midx-$(midx_checksum $objdir).rev &&
                rm -fr $midx &&
 
                # instead of constructing the snapshot ourselves (c.f., the test