kernel
/
git
mirror of https://git.kernel.org/pub/scm/git/git.git
1
0
Fork 0
Code Releases Activity

t5326: demonstrate bitmap corruption after permutation 

This patch demonstrates a cause of bitmap corruption that can occur when
the contents of the multi-pack index does not change, but the underlying
object order does.

In this example, we have a MIDX containing two packs, each with a
distinct set of objects (pack A corresponds to the tree, blob, and
commit from the first patch, and pack B corresponds to the second
patch).

First, a MIDX is written where the 'A' pack is preferred. As expected,
the bitmaps generated there are in-tact. But then, we generate an
identical MIDX with a different object order: this time preferring pack
'B'.

Due to a bug which will be explained and fixed in the following commit,
the MIDX is updated, but the .rev file is not, causing the .bitmap file
to be read incorrectly. Specifically, the .bitmap file will contain
correct data, but the auxiliary object order in the .rev file is stale,
causing readers to get confused by reading the new bitmaps using the old
object order.

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>
maint
Taylor Blau 2022-01-25 17:41:01 -05:00 committed by Junio C Hamano
parent dcc0cd074f
commit 61fd31a179
1 changed files with 31 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
t/t5326-multi-pack-bitmaps.sh
View File

@ -395,4 +395,35 @@ test_expect_success 'hash-cache values are propagated from pack bitmaps' '
)
'

test_expect_failure 'changing the preferred pack does not corrupt bitmaps' '
rm -fr repo &&
git init repo &&
test_when_finished "rm -fr repo" &&
(
cd repo &&

test_commit A &&
test_commit B &&

git rev-list --objects --no-object-names HEAD^ >A.objects &&
git rev-list --objects --no-object-names HEAD^.. >B.objects &&

A=$(git pack-objects $objdir/pack/pack <A.objects) &&
B=$(git pack-objects $objdir/pack/pack <B.objects) &&

cat >indexes <<-EOF &&
pack-$A.idx
pack-$B.idx
EOF

git multi-pack-index write --bitmap --stdin-packs \
--preferred-pack=pack-$A.pack <indexes &&
git rev-list --test-bitmap A &&

git multi-pack-index write --bitmap --stdin-packs \
--preferred-pack=pack-$B.pack <indexes &&
git rev-list --test-bitmap A
)
'

test_done