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We have a couple of tests that explicitly verify the structure of the
object database. Naturally, this structure is dependent on whether or
not we run repository maintenance: if it decides to optimize the object
database the expected structure is likely to not materialize.
Explicitly disable auto-maintenance in such tests so that we are not
dependent on decisions made by our maintenance.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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There are many tests that validate whether 'git pack-objects' works as
expected. Instead of duplicating these tests, add a new test environment
variable, GIT_TEST_PACK_PATH_WALK, that implies --path-walk by default
when specified.
This was useful in testing the implementation of the --path-walk
implementation, helping to find tests that are overly specific to the
default object walk. These include:
- t0411-clone-from-partial.sh : One test fetches from a repo that does
not have the boundary objects. This causes the path-based walk to
fail. Disable the variable for this test.
- t5306-pack-nobase.sh : Similar to t0411, one test fetches from a repo
without a boundary object.
- t5310-pack-bitmaps.sh : One test compares the case when packing with
bitmaps to the case when packing without them. Since we disable the
test variable when writing bitmaps, this causes a difference in the
object list (the --path-walk option adds an extra object). Specify
--no-path-walk in both processes for the comparison. Another test
checks for a specific delta base, but when computing dynamically
without using bitmaps, the base object it too small to be considered
in the delta calculations so no base is used.
- t5316-pack-delta-depth.sh : This script cares about certain delta
choices and their chain lengths. The --path-walk option changes how
these chains are selected, and thus changes the results of this test.
- t5322-pack-objects-sparse.sh : This demonstrates the effectiveness of
the --sparse option and how it combines with --path-walk.
- t5332-multi-pack-reuse.sh : This test verifies that the preferred
pack is used for delta reuse when possible. The --path-walk option is
not currently aware of the preferred pack at all, so finds a
different delta base.
- t7406-submodule-update.sh : When using the variable, the --depth
option collides with the --path-walk feature, resulting in a warning
message. Disable the variable so this warning does not appear.
I want to call out one specific test change that is only temporary:
- t5530-upload-pack-error.sh : One test cares specifically about an
"unable to read" error message. Since the current implementation
performs delta calculations within the path-walk API callback, a
different "unable to get size" error message appears. When this
is changed in a future refactoring, this test change can be reverted.
Similar to GIT_TEST_NAME_HASH_VERSION, we do not add this option to the
linux-TEST-vars CI build as that's already an overloaded build.
Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Leakfixes.
* ps/leakfixes-part-10: (27 commits)
t: remove TEST_PASSES_SANITIZE_LEAK annotations
test-lib: unconditionally enable leak checking
t: remove unneeded !SANITIZE_LEAK prerequisites
t: mark some tests as leak free
t5601: work around leak sanitizer issue
git-compat-util: drop now-unused `UNLEAK()` macro
global: drop `UNLEAK()` annotation
t/helper: fix leaking commit graph in "read-graph" subcommand
builtin/branch: fix leaking sorting options
builtin/init-db: fix leaking directory paths
builtin/help: fix leaks in `check_git_cmd()`
help: fix leaking return value from `help_unknown_cmd()`
help: fix leaking `struct cmdnames`
help: refactor to not use globals for reading config
builtin/sparse-checkout: fix leaking sanitized patterns
split-index: fix memory leak in `move_cache_to_base_index()`
git: refactor builtin handling to use a `struct strvec`
git: refactor alias handling to use a `struct strvec`
strvec: introduce new `strvec_splice()` function
line-log: fix leak when rewriting commit parents
...
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Now that the default value for TEST_PASSES_SANITIZE_LEAK is `true` there
is no longer a need to have that variable declared in all of our tests.
Drop it.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When reusing objects from source pack(s), write_reused_pack_verbatim()
is responsible for reusing objects whole eword_t's at a time. It works
by taking the longest continuous run of objects from the beginning of
each source pack that the caller wants, and reuses the entirety of that
section from each pack.
This is based on the assumption that we don't have any gaps within the
region. This assumption relieves us from having to patch any
OFS_DELTAs, since we know that there aren't any gaps between any delta
and its base in that region.
To illustrate why this assumption is necessary, suppose we have some
pack P, which has objects X, Y, and Z. If the MIDX's copy of Y was
selected from a pack other than P, then the bit corresponding to object
Y will appear earlier in the bitmap than the bits corresponding to X and
Z.
If pack-objects already has or will use the copy of Y from the pack it
was selected from in the MIDX, then it is an error to reuse all objects
between X and Z in the source pack. Doing so will cause us to reuse Y
from a different pack than the one which represents Y in the MIDX,
causing us to either:
- include the object twice, assuming that the caller wants Y in the
pack, or
- include the object once, resulting in us packing more objects than
necessary.
This regression comes from ca0fd69e37 (pack-objects: prepare
`write_reused_pack_verbatim()` for multi-pack reuse, 2023-12-14), which
incorrectly assumed that there would be no gaps in reusable regions of
non-preferred packs.
Instead, we can only safely perform the whole-word reuse optimization on
the preferred pack, where we know with certainty that no gaps exist in
that region of the bitmap. We can still reuse objects from non-preferred
packs, but we have to inspect them individually in write_reused_pack()
to ensure that any gaps that may exist are accounted for.
This allows us to simplify the implementation of
write_reused_pack_verbatim() back to almost its pre-multi-pack reuse
form, since we can now assume that the beginning of the pack appears at
the beginning of the bitmap, meaning that we don't have to account for
any bits up to the first word boundary (like we had to special case in
ca0fd69e37).
The only significant changes from the pre-ca0fd69e37 implementation are:
- that we can no longer inspect words up to the end of
reuse_packfile_bitmap->word_alloc, since we only want to look at
words whose bits all correspond to objects in the given packfile, and
- that we return early when given a reuse_packfile which is not
preferred, making the call a noop.
In the future, it might be possible to restore this optimization if we
could guarantee that some reuse packs don't contain any gaps by
construction (similar to the "disjoint packs" idea in very early
versions of multi-pack reuse).
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In the multi-pack reuse code, there are two paths for reusing the
on-disk representation of an object, handled by:
- builtin/pack-objects.c::write_reused_pack_one()
- builtin/pack-objects.c::write_reused_pack_verbatim()
The former is responsible for copying the bytes for a single object out
of an existing source pack. The latter does the same but for a region of
objects aligned at eword_t boundaries.
Demonstrate a bug whereby write_reused_pack_verbatim() can be tricked
into writing out objects from some source pack, even when those objects
were selected from a different source pack in the MIDX bitmap.
When the caller wants at least one of the objects in that region,
pack-objects will write the same object twice as a result of this bug.
In the other case where the caller doesn't want any of the objects in
the region of interest, we will write out objects that weren't
requested.
Demonstrate this bug by creating two packs, where the preferred one of
those packs contains a single object which also appears in the main
(non-preferred) pack. A separate bug[^1] prevents us from triggering the
main bug when the duplicated object is the last one in the main pack,
but any earlier object will suffice.
We could fix that separate bug, but the following commit will simplify
write_reused_pack_verbatim() and only call it on the preferred pack, so
doing so would have little point.
[^1]: Because write_reused_pack_verbatim() only reuses bits in the range
off_t pack_start_off = pack_pos_to_offset(reuse_packfile->p, 0);
off_t pack_end_off = pack_pos_to_offset(reuse_packfile->p,
pos - reuse_packfile->bitmap_pos);
written += pos - reuse_packfile->bitmap_pos;
/* We're recording one chunk, not one object. */
record_reused_object(pack_start_off,
pack_start_off - (hashfile_total(out) - pack_start));
, or in other words excluding the object beginning at position 'pos -
reuse_packfile->bitmap_pos' in the source pack. But since
reuse_packfile->bitmap_pos is '1' in the non-preferred pack
(accounting for the single-object pack which is preferred), we don't
actually copy the bytes from the last object.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When reusing chunks verbatim from an existing source pack, the function
write_reused_pack() first attempts to reuse whole words (via the
function `write_reused_pack_verbatim()`), and then individual bits (via
`write_reused_pack_one()`).
In the non-MIDX case, all of this code works fine. Likewise, in the MIDX
case, processing bits individually from the first (preferred) pack works
fine. However, processing subsequent packs in the MIDX case is broken
when there are duplicate objects among the set of MIDX'd packs.
This is because we treat the individual bit positions as valid pack
positions within the source pack(s), which does not account for gaps in
the source pack, like we see when the MIDX must break ties between
duplicate objects which appear in multiple packs.
The broken code looks like:
for (; i < reuse_packfile_bitmap->word_alloc; i++) {
for (offset = 0; offset < BITS_IN_EWORD, offset++) {
/* ... */
write_reused_pack_one(reuse_packfile->p,
pos + offset - reuse_packfile->bitmap_pos,
f, pack_start, &w_curs);
}
}
, where the second argument is incorrect and does not account for gaps.
Instead, make sure that we translate bit positions in the MIDX's
pseudo-pack order to pack positions in the respective source packs by:
- Translating the bit position (pseudo-pack order) to a MIDX position
(lexical order).
- Use the MIDX position to obtain the offset at which the given object
occurs in the source pack.
- Then translate that offset back into a pack relative position within
the source pack by calling offset_to_pack_pos().
After doing this, then we can safely use the result as a pack position.
Note that when doing single-pack reuse, as well as reusing objects from
the MIDX's preferred pack, such translation is not necessary, since
either ties are broken in favor of the preferred pack, or there are no
ties to break at all (in the case of non-MIDX bitmaps).
Failing to do this can result in strange failure modes. One example that
can occur when misinterpreting bits in the above fashion is that Git
thinks it's supposed to send a delta that the caller does not want.
Under this (incorrect) assumption, we try to look up the delta's base
(so that we can patch any OFS_DELTAs if necessary). We do this using
find_reused_offset().
But if we try and call that function for an offset belonging to an
object we did not send, we'll get back garbage. This can result in us
computing a negative fixup value, which results in memory corruption
when trying to write the (patched) OFS_DELTA header.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In our tests for multi-pack reuse, we have two helper functions:
- test_pack_objects_reused_all(), and
- test_pack_objects_reused()
which invoke pack-objects (either with `--all`, or the supplied tips via
stdin, respectively) and ensure that (a) the number of reused objects,
and (b) the number of packs which those objects were reused from both
match the expected values.
Both functions discard the output of pack-objects and assert only on the
contents of the trace2 stream.
However, if we store the pack and attempt to index it with `--strict`,
we find that a number of our tests are broken, indicating a bug within
multi-pack reuse.
That bug will be addressed in a subsequent commit. But let's first
harden these tests by trying to index the resulting pack, marking the
tests which fail appropriately.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that the rest of the MIDX subsystem and relevant callers have been
updated to learn about how to read and process incremental MIDX chains,
let's finally update the implementation in `write_midx_internal()` to be
able to write incremental MIDX chains.
This new feature is available behind the `--incremental` option for the
`multi-pack-index` builtin, like so:
$ git multi-pack-index write --incremental
The implementation for doing so is relatively straightforward, and boils
down to a handful of different kinds of changes implemented in this
patch:
- The `compute_sorted_entries()` function is taught to reject objects
which appear in any existing MIDX layer.
- Functions like `write_midx_revindex()` are adjusted to write
pack_order values which are offset by the number of objects in the
base MIDX layer.
- The end of `write_midx_internal()` is adjusted to move
non-incremental MIDX files when necessary (i.e. when creating an
incremental chain with an existing non-incremental MIDX in the
repository).
There are a handful of other changes that are introduced, like new
functions to clear incremental MIDX files that are unrelated to the
current chain (using the same "keep_hash" mechanism as in the
non-incremental case).
The tests explicitly exercising the new incremental MIDX feature are
relatively limited for two reasons:
1. Most of the "interesting" behavior is already thoroughly covered in
t5319-multi-pack-index.sh, which handles the core logic of reading
objects through a MIDX.
The new tests in t5334-incremental-multi-pack-index.sh are mostly
focused on creating and destroying incremental MIDXs, as well as
stitching their results together across layers.
2. A new GIT_TEST environment variable is added called
"GIT_TEST_MULTI_PACK_INDEX_WRITE_INCREMENTAL", which modifies the
entire test suite to write incremental MIDXs after repacking when
combined with the "GIT_TEST_MULTI_PACK_INDEX" variable.
This exercises the long tail of other interesting behavior that is
defined implicitly throughout the rest of the CI suite. It is
likewise added to the linux-TEST-vars job.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When performing multi-pack reuse, reuse_partial_packfile_from_bitmap()
is responsible for generating an array of bitmapped_pack structs from
which to perform reuse.
In the multi-pack case, we loop over the MIDXs packs and copy the result
of calling `nth_bitmapped_pack()` to construct the list of reusable
paths.
But we may also want to do pack-reuse over a single pack, either because
we only had one pack to perform reuse over (in the case of single-pack
bitmaps), or because we explicitly asked to do single pack reuse even
with a MIDX[^1].
When this is the case, the array we generate of reusable packs contains
only a single element, which is either (a) the pack attached to the
single-pack bitmap, or (b) the MIDX's preferred pack.
In 795006fff4 (pack-bitmap: gracefully handle missing BTMP chunks,
2024-04-15), we refactored the reuse_partial_packfile_from_bitmap()
function and stopped assigning the pack_int_id field when reusing only
the MIDX's preferred pack. This results in an uninitialized read down in
try_partial_reuse() like so:
==7474==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x55c5cd191dde in try_partial_reuse pack-bitmap.c:1887:8
#1 0x55c5cd191dde in reuse_partial_packfile_from_bitmap_1 pack-bitmap.c:2001:8
#2 0x55c5cd191dde in reuse_partial_packfile_from_bitmap pack-bitmap.c:2105:3
#3 0x55c5cce0bd0e in get_object_list_from_bitmap builtin/pack-objects.c:4043:3
#4 0x55c5cce0bd0e in get_object_list builtin/pack-objects.c:4156:27
#5 0x55c5cce0bd0e in cmd_pack_objects builtin/pack-objects.c:4596:3
#6 0x55c5ccc8fac8 in run_builtin git.c:474:11
which happens when try_partial_reuse() tries to call
midx_pair_to_pack_pos() when it tries to reject cross-pack deltas.
Avoid the uninitialized read by ensuring that the pack_int_id field is
set in the single-pack reuse case by setting it to either the MIDX
preferred pack's pack_int_id, or '-1', in the case of single-pack
bitmaps. In the latter case, we never read the pack_int_id field, so
the choice of '-1' is intentional as a "garbage in, garbage out"
measure.
Guard against further regressions in this area by adding a test which
ensures that we do not throw out deltas from the preferred pack as
"cross-pack" due to an uninitialized pack_int_id.
[^1]: This can happen for a couple of reasons, either because the
repository is configured with 'pack.allowPackReuse=(true|single)', or
because the MIDX was generated prior to the introduction of the BTMP
chunk, which contains information necessary to perform multi-pack
reuse.
Reported-by: Kyle Lippincott <spectral@google.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Setting `feature.experimental` opts the user into multi-pack reuse
experiment
* tb/multi-pack-reuse-experiment:
pack-objects: enable multi-pack reuse via `feature.experimental`
t5332-multi-pack-reuse.sh: extract pack-objects helper functions
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Now that multi-pack reuse is supported, enable it via the
feature.experimental configuration in addition to the classic
`pack.allowPackReuse`.
This will allow more users to experiment with the new behavior who might
not otherwise be aware of the existing `pack.allowPackReuse`
configuration option.
The enum with values NO_PACK_REUSE, SINGLE_PACK_REUSE, and
MULTI_PACK_REUSE is defined statically in builtin/pack-objects.c's
compilation unit. We could hoist that enum into a scope visible from the
repository_settings struct, and then use that enum value in
pack-objects. Instead, define a single int that indicates what
pack-objects's default value should be to avoid additional unnecessary
code movement.
Though `feature.experimental` implies `pack.allowPackReuse=multi`, this
can still be overridden by explicitly setting the latter configuration
to either "single" or "false". Tests covering all of these cases are
showin t5332.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Most of the tests in t5332 perform some setup before repeating a common
refrain that looks like:
: >trace2.txt &&
GIT_TRACE2_EVENT="$PWD/trace2.txt" \
git pack-objects --stdout --revs --all >/dev/null &&
test_pack_reused $objects_nr <trace2.txt &&
test_packs_reused $packs_nr <trace2.txt
The next commit will add more tests which repeat the above refrain.
Avoid duplicating this invocation even further and prepare for the
following commit by wrapping the above in a helper function called
`test_pack_objects_reused_all()`.
Introduce another similar function `test_pack_objects_reused`, which
expects to read a list of revisions over stdin for tests which need more
fine-grained control of the contents of the pack they generate.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This test is leak-free since it was added in af626ac0e0 (pack-bitmap:
enable reuse from all bitmapped packs, 2023-12-14).
Let's mark it as leak-free to make sure it stays that way (and to reduce
noise when looking for other leak-free scripts after we fix some leaks).
Signed-off-by: Rubén Justo <rjusto@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Now that both the pack-bitmap and pack-objects code are prepared to
handle marking and using objects from multiple bitmapped packs for
verbatim reuse, allow marking objects from all bitmapped packs as
eligible for reuse.
Within the `reuse_partial_packfile_from_bitmap()` function, we no longer
only mark the pack whose first object is at bit position zero for reuse,
and instead mark any pack contained in the MIDX as a reuse candidate.
Provide a handful of test cases in a new script (t5332) exercising
interesting behavior for multi-pack reuse to ensure that we performed
all of the previous steps correctly.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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