More code paths have a repository passed through the callchain,
instead of assuming the primary the_repository object.
* ps/the-repository:
match-trees: stop using `the_repository`
graph: stop using `the_repository`
add-interactive: stop using `the_repository`
tmp-objdir: stop using `the_repository`
resolve-undo: stop using `the_repository`
credential: stop using `the_repository`
mailinfo: stop using `the_repository`
diagnose: stop using `the_repository`
server-info: stop using `the_repository`
send-pack: stop using `the_repository`
serve: stop using `the_repository`
trace: stop using `the_repository`
pager: stop using `the_repository`
progress: stop using `the_repository`
Code to reuse objects based on bitmap contents have been tightened
to avoid race condition even when multiple packs are involved.
* tb/bitmap-fix-pack-reuse:
pack-bitmap.c: ensure pack validity for all reuse packs
Start working to make the codebase buildable with -Wsign-compare.
* ps/build-sign-compare:
t/helper: don't depend on implicit wraparound
scalar: address -Wsign-compare warnings
builtin/patch-id: fix type of `get_one_patchid()`
builtin/blame: fix type of `length` variable when emitting object ID
gpg-interface: address -Wsign-comparison warnings
daemon: fix type of `max_connections`
daemon: fix loops that have mismatching integer types
global: trivial conversions to fix `-Wsign-compare` warnings
pkt-line: fix -Wsign-compare warning on 32 bit platform
csum-file: fix -Wsign-compare warning on 32-bit platform
diff.h: fix index used to loop through unsigned integer
config.mak.dev: drop `-Wno-sign-compare`
global: mark code units that generate warnings with `-Wsign-compare`
compat/win32: fix -Wsign-compare warning in "wWinMain()"
compat/regex: explicitly ignore "-Wsign-compare" warnings
git-compat-util: introduce macros to disable "-Wsign-compare" warnings
Stop using `the_repository` in the "progress" subsystem by passing in a
repository when initializing `struct progress`. Furthermore, store a
pointer to the repository in that struct so that we can pass it to the
trace2 API when logging information.
Adjust callers accordingly by using `the_repository`. While there may be
some callers that have a repository available in their context, this
trivial conversion allows for easier verification and bubbles up the use
of `the_repository` by one level.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* ps/build-sign-compare:
t/helper: don't depend on implicit wraparound
scalar: address -Wsign-compare warnings
builtin/patch-id: fix type of `get_one_patchid()`
builtin/blame: fix type of `length` variable when emitting object ID
gpg-interface: address -Wsign-comparison warnings
daemon: fix type of `max_connections`
daemon: fix loops that have mismatching integer types
global: trivial conversions to fix `-Wsign-compare` warnings
pkt-line: fix -Wsign-compare warning on 32 bit platform
csum-file: fix -Wsign-compare warning on 32-bit platform
diff.h: fix index used to loop through unsigned integer
config.mak.dev: drop `-Wno-sign-compare`
global: mark code units that generate warnings with `-Wsign-compare`
compat/win32: fix -Wsign-compare warning in "wWinMain()"
compat/regex: explicitly ignore "-Wsign-compare" warnings
git-compat-util: introduce macros to disable "-Wsign-compare" warnings
Commit 44f9fd6496 (pack-bitmap.c: check preferred pack validity when
opening MIDX bitmap, 2022-05-24) prevents a race condition whereby the
preferred pack disappears between opening the MIDX bitmap and attempting
verbatim reuse out of its packs.
That commit forces open_midx_bitmap_1() to ensure the validity of the
MIDX's preferred pack, meaning that we have an open file handle on the
*.pack, ensuring that we can reuse bytes out of verbatim later on in the
process[^1].
But 44f9fd6496 was not extended to cover multi-pack reuse, meaning that
this same race condition exists for non-preferred packs during verbatim
reuse. Work around that race in the same way by only marking valid packs
as reuse-able. For packs that aren't reusable, skip over them but
include the number of objects they have to ensure we allocate a large
enough 'reuse' bitmap (e.g. if a pack in the middle of the MIDX
disappeared but we still want to reuse later packs).
Since we're ensuring the validity of these packs within the verbatim
reuse code, we no longer have to special-case the preferred pack and
open it within the open_midx_bitmap_1() function.
An alternative approach to the one taken here would be to open all
MIDX'd packs from within open_midx_bitmap_1(). But that would be both
slower and make the bitmaps less useful, since we can still perform some
pack reuse among the packs that still exist when the *.bitmap is opened.
After applying this patch, we can simulate the new behavior after
instrumenting Git like so:
diff --git a/packfile.c b/packfile.c
index 9560f0a33c..aedce72524 100644
--- a/packfile.c
+++ b/packfile.c
@@ -557,6 +557,11 @@ static int open_packed_git_1(struct packed_git *p)
; /* nothing */
p->pack_fd = git_open(p->pack_name);
+ {
+ const char *delete = getenv("GIT_RACILY_DELETE");
+ if (delete && !strcmp(delete, pack_basename(p)))
+ return -1;
+ }
if (p->pack_fd < 0 || fstat(p->pack_fd, &st))
return -1;
pack_open_fds++;
and adding the following test:
test_expect_success 'disappearing packs' '
git init disappearing-packs &&
(
cd disappearing-packs &&
git config pack.allowPackReuse multi &&
test_commit A &&
test_commit B &&
test_commit C &&
A="$(echo "A" | git pack-objects --revs $packdir/pack-A)" &&
B="$(echo "A..B" | git pack-objects --revs $packdir/pack-B)" &&
C="$(echo "B..C" | git pack-objects --revs $packdir/pack-C)" &&
git multi-pack-index write --bitmap --preferred-pack=pack-A-$A.idx &&
test_pack_objects_reused_all 9 3 &&
test_env GIT_RACILY_DELETE=pack-A-$A.pack \
test_pack_objects_reused_all 6 2 &&
test_env GIT_RACILY_DELETE=pack-B-$B.pack \
test_pack_objects_reused_all 6 2 &&
test_env GIT_RACILY_DELETE=pack-C-$C.pack \
test_pack_objects_reused_all 6 2
)
'
Note that we could relax the single-pack version of this which was most
recently addressed in dc1daacdcc (pack-bitmap: check pack validity when
opening bitmap, 2021-07-23), but only partially. Because we still need
to know the object count in the pack, we'd still have to open the pack's
*.idx, so the savings there are marginal.
Note likewise that we add a new "if (!packs_nr)" early return in the
pack reuse code to avoid a potentially expensive allocation on the
'reuse' bitmap in the case that no packs are available for reuse.
[^1]: Unless we run out of open file handles. If that happens and we are
forced to close the only open file handle of a file that has been
removed from underneath us, there is nothing we can do.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Yet another "pass the repository through the callchain" topic.
* kn/midx-wo-the-repository:
midx: inline the `MIDX_MIN_SIZE` definition
midx: pass down `hash_algo` to functions using global variables
midx: pass `repository` to `load_multi_pack_index`
midx: cleanup internal usage of `the_repository` and `the_hash_algo`
midx-write: pass down repository to `write_midx_file[_only]`
write-midx: add repository field to `write_midx_context`
midx-write: use `revs->repo` inside `read_refs_snapshot`
midx-write: pass down repository to static functions
packfile.c: remove unnecessary prepare_packed_git() call
midx: add repository to `multi_pack_index` struct
config: make `packed_git_(limit|window_size)` non-global variables
config: make `delta_base_cache_limit` a non-global variable
packfile: pass down repository to `for_each_packed_object`
packfile: pass down repository to `has_object[_kept]_pack`
packfile: pass down repository to `odb_pack_name`
packfile: pass `repository` to static function in the file
packfile: use `repository` from `packed_git` directly
packfile: add repository to struct `packed_git`
Mark code units that generate warnings with `-Wsign-compare`. This
allows for a structured approach to get rid of all such warnings over
time in a way that can be easily measured.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The functions `get_split_midx_filename_ext()`, `get_midx_filename()` and
`get_midx_filename_ext()` use `hash_to_hex()` which internally uses the
`the_hash_algo` global variable.
Remove this dependency on global variables by passing down the
`hash_algo` through to the functions mentioned and instead calling
`hash_to_hex_algop()` along with the obtained `hash_algo`.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `multi_pack_index` struct represents the MIDX for a repository.
Here, we add a pointer to the repository in this struct, allowing direct
use of the repository variable without relying on the global
`the_repository` struct.
With this addition, we can determine the repository associated with a
`bitmap_index` struct. A `bitmap_index` points to either a `packed_git`
or a `multi_pack_index`, both of which have direct repository
references. To support this, we introduce a static helper function,
`bitmap_repo`, in `pack-bitmap.c`, which retrieves a repository given a
`bitmap_index`.
With this, we clear up all usages of `the_repository` within
`pack-bitmap.c` and also remove the `USE_THE_REPOSITORY_VARIABLE`
definition. Bringing us another step closer to remove all global
variable usage.
Although this change also opens up the potential to clean up `midx.c`,
doing so would require additional refactoring to pass the repository
struct to functions where the MIDX struct is created: a task better
suited for future patches.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The functions `has_object[_kept]_pack` currently rely on the global
variable `the_repository`. To eliminate global variable usage in
`packfile.c`, we should progressively shift the dependency on
the_repository to higher layers. Let's remove its usage from these
functions and any related ones.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the boundary-based bitmap traversal, we use the given 'rev_info'
structure to first do a commit-only walk in order to determine the
boundary between interesting and uninteresting objects.
That walk only looks at commit objects, regardless of the state of
revs->blob_objects, revs->tree_objects, and so on. In order to do this,
we store the state of these variables in temporary fields before
setting them back to zero, performing the traversal, and then setting
them back.
But there is a typo here that dates back to b0afdce5da (pack-bitmap.c:
use commit boundary during bitmap traversal, 2023-05-08), where we
incorrectly store the value of the "tags" field as "revs->blob_objects".
This could lead to problems later on if, say, the caller wants tag
objects but *not* blob objects. In the pre-image behavior, we'd set
revs->tag_objects back to the old value of revs->blob_objects, thus
emitting fewer objects than expected back to the caller.
Fix that by correctly assigning the value of 'revs->tag_objects' to the
'tmp_tags' field.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The main function we use to search a pack index for an object is
find_pack_entry_one(). That function still takes a bare pointer to the
hash, despite the fact that its underlying bsearch_pack() function needs
an object_id struct. And so we end up making an extra copy of the hash
into the struct just to do a lookup.
As it turns out, all callers but one already have such an object_id. So
we can just take a pointer to that struct and use it directly. This
avoids the extra copy and provides a more type-safe interface.
The one exception is get_delta_base() in packfile.c, when we are chasing
a REF_DELTA from inside the pack (and thus we have a pointer directly to
the mmap'd pack memory, not a struct). We can just bump the hashcpy()
from inside find_pack_entry_one() to this one caller that needs it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Fix various memory leaks hit by the pseudo-merge machinery. These leaks
are exposed by t5333, but plugging them does not yet make the whole test
suite pass.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When calling `try_partial_reuse()`, the (sole) caller from the function
`reuse_partial_packfile_from_bitmap_1()` has to translate its bit
position to a pack position.
In the MIDX bitmap case, the caller translates from the bit position, to
a position in the MIDX's pseudo-pack order (with `pack_pos_to_midx()`),
then get a pack offset (with `nth_midxed_offset()`) before finally
working backwards to get the pack position in the source pack by calling
`offset_to_pack_pos()`.
In the non-MIDX bitmap case, we can use the bit position as the pack
position directly (see the comment at the beginning of the
`reuse_partial_packfile_from_bitmap_1()` function for why).
In either case, the first thing that `try_partial_reuse()` does after
being called is determine the offset of the object at the given pack
position by calling `pack_pos_to_offset()`. But we already have that
information in the MIDX case!
Avoid re-computing that information by instead passing it in. In the
MIDX case, we already have that information stored. In the non-MIDX
case, the call to `pack_pos_to_offset()` moves from the function
`try_partial_reuse()` to its caller. In total, we'll save one call to
`pack_pos_to_offset()` when processing MIDX bitmaps.
(On my machine, there is a slight speed-up on the order of ~2ms, but it
is within the margin of error over 10 runs, so I think you'd have to
have a truly gigantic repository to confidently measure any significant
improvement here).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The next commit will need to use the bitmap's MIDX (if one exists) to
translate bit positions into pack-relative positions in the source pack.
Ordinarily, we'd use the "midx" field of the bitmap_index struct. But
since that struct is defined within pack-bitmap.c, and our caller is in
a separate compilation unit, we do not have access to the MIDX field.
Instead, add a "from_midx" field to the bitmapped_pack structure so that
we can use that piece of data from outside of pack-bitmap.c. The caller
that uses this new piece of information will be added in the following
commit.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
A CPP macro USE_THE_REPOSITORY_VARIABLE is introduced to help
transition the codebase to rely less on the availability of the
singleton the_repository instance.
* ps/use-the-repository:
hex: guard declarations with `USE_THE_REPOSITORY_VARIABLE`
t/helper: remove dependency on `the_repository` in "proc-receive"
t/helper: fix segfault in "oid-array" command without repository
t/helper: use correct object hash in partial-clone helper
compat/fsmonitor: fix socket path in networked SHA256 repos
replace-object: use hash algorithm from passed-in repository
protocol-caps: use hash algorithm from passed-in repository
oidset: pass hash algorithm when parsing file
http-fetch: don't crash when parsing packfile without a repo
hash-ll: merge with "hash.h"
refs: avoid include cycle with "repository.h"
global: introduce `USE_THE_REPOSITORY_VARIABLE` macro
hash: require hash algorithm in `empty_tree_oid_hex()`
hash: require hash algorithm in `is_empty_{blob,tree}_oid()`
hash: make `is_null_oid()` independent of `the_repository`
hash: convert `oidcmp()` and `oideq()` to compare whole hash
global: ensure that object IDs are always padded
hash: require hash algorithm in `oidread()` and `oidclr()`
hash: require hash algorithm in `hasheq()`, `hashcmp()` and `hashclr()`
hash: drop (mostly) unused `is_empty_{blob,tree}_sha1()` functions
The pseudo-merge reachability bitmap to help more efficient storage
of the reachability bitmap in a repository with too many refs has
been added.
* tb/pseudo-merge-reachability-bitmap: (26 commits)
pack-bitmap.c: ensure pseudo-merge offset reads are bounded
Documentation/technical/bitmap-format.txt: add missing position table
t/perf: implement performance tests for pseudo-merge bitmaps
pseudo-merge: implement support for finding existing merges
ewah: `bitmap_equals_ewah()`
pack-bitmap: extra trace2 information
pack-bitmap.c: use pseudo-merges during traversal
t/test-lib-functions.sh: support `--notick` in `test_commit_bulk()`
pack-bitmap: implement test helpers for pseudo-merge
ewah: implement `ewah_bitmap_popcount()`
pseudo-merge: implement support for reading pseudo-merge commits
pack-bitmap.c: read pseudo-merge extension
pseudo-merge: scaffolding for reads
pack-bitmap: extract `read_bitmap()` function
pack-bitmap-write.c: write pseudo-merge table
pseudo-merge: implement support for selecting pseudo-merge commits
config: introduce `git_config_double()`
pack-bitmap: make `bitmap_writer_push_bitmapped_commit()` public
pack-bitmap: implement `bitmap_writer_has_bitmapped_object_id()`
pack-bitmap-write: support storing pseudo-merge commits
...
After reading the pseudo-merge extension's metadata table, we allocate
an array to store information about each pseudo-merge, including its
byte offset within the .bitmap file itself.
This is done like so:
pseudo_merge_ofs = index_end - 24 -
(index->pseudo_merges.nr * sizeof(uint64_t));
for (i = 0; i < index->pseudo_merges.nr; i++) {
index->pseudo_merges.v[i].at = get_be64(pseudo_merge_ofs);
pseudo_merge_ofs += sizeof(uint64_t);
}
But if the pseudo-merge table is corrupt, we'll keep calling get_be64()
past the end of the pseudo-merge extension, potentially reading off the
end of the mmap'd region.
Prevent this by ensuring that we have at least `table_size - 24` many
bytes available to read (adding 24 to the left-hand side of our
inequality to account for the length of the metadata component).
This is sufficient to prevent us from reading off the end of the
pseudo-merge extension, and ensures that all of the get_be64() calls
below are in bounds.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Use of the `the_repository` variable is deprecated nowadays, and we
slowly but steadily convert the codebase to not use it anymore. Instead,
callers should be passing down the repository to work on via parameters.
It is hard though to prove that a given code unit does not use this
variable anymore. The most trivial case, merely demonstrating that there
is no direct use of `the_repository`, is already a bit of a pain during
code reviews as the reviewer needs to manually verify claims made by the
patch author. The bigger problem though is that we have many interfaces
that implicitly rely on `the_repository`.
Introduce a new `USE_THE_REPOSITORY_VARIABLE` macro that allows code
units to opt into usage of `the_repository`. The intent of this macro is
to demonstrate that a certain code unit does not use this variable
anymore, and to keep it from new dependencies on it in future changes,
be it explicit or implicit
For now, the macro only guards `the_repository` itself as well as
`the_hash_algo`. There are many more known interfaces where we have an
implicit dependency on `the_repository`, but those are not guarded at
the current point in time. Over time though, we should start to add
guards as required (or even better, just remove them).
Define the macro as required in our code units. As expected, most of our
code still relies on the global variable. Nearly all of our builtins
rely on the variable as there is no way yet to pass `the_repository` to
their entry point. For now, declare the macro in "biultin.h" to keep the
required changes at least a little bit more contained.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Many of our hash functions have two variants, one receiving a `struct
git_hash_algo` and one that derives it via `the_repository`. Adapt all
of those functions to always require the hash algorithm as input and
drop the variants that do not accept one.
As those functions are now independent of `the_repository`, we can move
them from "hash.h" to "hash-ll.h".
Note that both in this and subsequent commits in this series we always
just pass `the_repository->hash_algo` as input even if it is obvious
that there is a repository in the context that we should be using the
hash from instead. This is done to be on the safe side and not introduce
any regressions. All callsites should eventually be amended to use a
repo passed via parameters, but this is outside the scope of this patch
series.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
Now that we have the `get_midx_filename_ext()` helper, we can
reimplement the `midx_bitmap_filename()` function in terms of it.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This patch implements support for reusing existing pseudo-merge commits
when writing bitmaps when there is an existing pseudo-merge bitmap which
has exactly the same set of parents as one that we are about to write.
Note that unstable pseudo-merges are likely to change between
consecutive repacks, and so are generally poor candidates for reuse.
However, stable pseudo-merges (see the configuration option
'bitmapPseudoMerge.<name>.stableThreshold') are by definition unlikely
to change between runs (as they represent long-running branches).
Because there is no index from a *set* of pseudo-merge parents to a
matching pseudo-merge bitmap, we have to construct the bitmap
corresponding to the set of parents for each pending pseudo-merge commit
and see if a matching bitmap exists.
This is technically quadratic in the number of pseudo-merges, but is OK
in practice for a couple of reasons:
- non-matching pseudo-merge bitmaps are rejected quickly as soon as
they differ in a single bit
- already-matched pseudo-merge bitmaps are discarded from subsequent
rounds of search
- the number of pseudo-merges is generally small, even for large
repositories
In order to do this, implement (a) a function that finds a matching
pseudo-merge given some uncompressed bitset describing its parents, (b)
a function that computes the bitset of parents for a given pseudo-merge
commit, and (c) call that function before computing the set of reachable
objects for some pending pseudo-merge.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add some extra trace2 lines to capture the number of bitmap lookups that
are hits versus misses, as well as the number of reachability roots that
have bitmap coverage (versus those that do not).
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that all of the groundwork has been laid to support reading and
using pseudo-merges, make use of that work in this commit by teaching
the pack-bitmap machinery to use pseudo-merge(s) when available during
traversal.
The basic operation is as follows:
- When enumerating objects on either side of a reachability query,
first see if any subset of the roots satisfies some pseudo-merge
bitmap. If it does, apply that pseudo-merge bitmap.
- If any pseudo-merge bitmap(s) were applied in the previous step, OR
them into the result[^1]. Then repeat the process over all
pseudo-merge bitmaps (we'll refer to this as "cascading"
pseudo-merges). Once this is done, OR in the resulting bitmap.
- If there is no fill-in traversal to be done, return the bitmap for
that side of the reachability query. If there is fill-in traversal,
then for each commit we encounter via show_commit(), check to see if
any unsatisfied pseudo-merges containing that commit as one of its
parents has been made satisfied by the presence of that commit.
If so, OR in the object set from that pseudo-merge bitmap, and then
cascade. If not, continue traversal.
A similar implementation is present in the boundary-based bitmap
traversal routines.
[^1]: Importantly, we cannot OR in the entire set of roots along with
the objects reachable from whatever pseudo-merge bitmaps were
satisfied. This may leave some dangling bits corresponding to any
unsatisfied root(s) getting OR'd into the resulting bitmap, tricking
other parts of the traversal into thinking we already have a
reachability closure over those commit(s) when we do not.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Implement three new sub-commands for the "bitmap" test-helper:
- t/helper test-tool bitmap dump-pseudo-merges
- t/helper test-tool bitmap dump-pseudo-merge-commits <n>
- t/helper test-tool bitmap dump-pseudo-merge-objects <n>
These three helpers dump the list of pseudo merges, the "parents" of the
nth pseudo-merges, and the set of objects reachable from those parents,
respectively.
These helpers will be useful in subsequent patches when we add test
coverage for pseudo-merge bitmaps.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that the scaffolding for reading the pseudo-merge extension has been
laid, teach the pack-bitmap machinery to read the pseudo-merge extension
when present.
Note that pseudo-merges themselves are not yet used during traversal,
this step will be taken by a future commit.
In the meantime, read the table and initialize the pseudo_merge_map
structure introduced by a previous commit. When the pseudo-merge
extension is present, `load_bitmap_header()` performs basic sanity
checks to make sure that the table is well-formed.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The pack-bitmap machinery uses the `read_bitmap_1()` function to read a
bitmap from within the mmap'd region corresponding to the .bitmap file.
As as side-effect of calling this function, `read_bitmap_1()` increments
the `index->map_pos` variable to reflect the number of bytes read.
Extract the core of this routine to a separate function (that operates
over a `const unsigned char *`, a `size_t` and a `size_t *` pointer)
instead of a `struct bitmap_index *` pointer.
This function (called `read_bitmap()`) is part of the pack-bitmap.h API
so that it can be used within the upcoming portion of the implementation
in pseduo-merge.ch.
Rewrite the existing function, `read_bitmap_1()`, in terms of its more
generic counterpart.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
GIt 2.44 introduced a regression that makes the updated code to
barf in repositories with multi-pack index written by older
versions of Git, which has been corrected.
* ps/missing-btmp-fix:
pack-bitmap: gracefully handle missing BTMP chunks
In 0fea6b73f1 (Merge branch 'tb/multi-pack-verbatim-reuse', 2024-01-12)
we have introduced multi-pack verbatim reuse of objects. This series has
introduced a new BTMP chunk, which encodes information about bitmapped
objects in the multi-pack index. Starting with dab60934e3 (pack-bitmap:
pass `bitmapped_pack` struct to pack-reuse functions, 2023-12-14) we use
this information to figure out objects which we can reuse from each of
the packfiles.
One thing that we glossed over though is backwards compatibility with
repositories that do not yet have BTMP chunks in their multi-pack index.
In that case, `nth_bitmapped_pack()` would return an error, which causes
us to emit a warning followed by another error message. These warnings
are visible to users that fetch from a repository:
```
$ git fetch
...
remote: error: MIDX does not contain the BTMP chunk
remote: warning: unable to load pack: 'pack-f6bb7bd71d345ea9fe604b60cab9ba9ece54ffbe.idx', disabling pack-reuse
remote: Enumerating objects: 40, done.
remote: Counting objects: 100% (40/40), done.
remote: Compressing objects: 100% (39/39), done.
remote: Total 40 (delta 5), reused 0 (delta 0), pack-reused 0 (from 0)
...
```
While the fetch succeeds the user is left wondering what they did wrong.
Furthermore, as visible both from the warning and from the reuse stats,
pack-reuse is completely disabled in such repositories.
What is quite interesting is that this issue can even be triggered in
case `pack.allowPackReuse=single` is set, which is the default value.
One could have expected that in this case we fall back to the old logic,
which is to use the preferred packfile without consulting BTMP chunks at
all. But either we fail with the above error in case they are missing,
or we use the first pack in the multi-pack-index. The former case
disables pack-reuse altogether, whereas the latter case may result in
reusing objects from a suboptimal packfile.
Fix this issue by partially reverting the logic back to what we had
before this patch series landed. Namely, in the case where we have no
BTMP chunks or when `pack.allowPackReuse=single` are set, we use the
preferred pack instead of consulting the BTMP chunks.
Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This variable is no longer used for doing verbatim pack-reuse (or
anywhere within pack-bitmap.c) since d2ea031046 (pack-bitmap: don't rely
on bitmap_git->reuse_objects, 2019-12-18).
Remove it to avoid an unused struct member.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
Now that the pack-objects code is equipped to handle reusing objects
from multiple packs, prepare the pack-bitmap code to mark objects from
multiple packs as reuse candidates.
In order to prepare the pack-bitmap code for this change, remove the
same set of assumptions we unwound in previous commits from the helper
function `reuse_partial_packfile_from_bitmap_1()`, in preparation for it
to be called in a loop over the set of bitmapped packs in a following
commit.
Most importantly, we can no longer assume that the bit position
corresponding to the first object in a given reuse pack candidate is at
the beginning of the bitmap itself.
For the single pack that this assumption is still true for (in MIDX
bitmaps, this is the preferred pack, in single-pack bitmaps it is the
pack the bitmap is tied to), we can still use our whole-words
optimization.
But for all subsequent packs, we can not make use of this optimization,
since it assumes that all delta bases are being sent from the same pack,
which would break if we are sending OFS_DELTAs down to the client. To
understand why, consider two packs, P1 and P2 where:
- P1 has object A which is a delta on base B
- P2 has its own copy of B, in addition to other objects
Suppose that the MIDX which covers P1 and P2 selected its copy of A from
P1, but selected its copy of B from P2. Since A is a delta of B, but the
base was selected from a different pack, sending the bytes corresponding
to A as an OFS_DELTA verbatim from P1 would be incorrect, since we don't
guarantee that B is in the same place relative to A in the generated
pack as in P1.
For now, we detect and reject these cross-pack deltas by searching for
the (pack_id, offset) pair for the delta's base object (using the same
pack_id as the pack containing the delta'd object) in the MIDX. If we
find a match, that means that the MIDX did indeed pick the base object
from the same pack, and we are OK to reuse the delta.
If we don't find a match, however, that means that the base object was
selected from a different pack in the MIDX, and we can let the slower
path handle re-delta'ing our candidate object.
In the future, there are a couple of other things we could do, namely:
- Turn any cross-pack deltas (which are stored as OFS_DELTAs) into
REF_DELTAs. We already do this today when reusing an OFS_DELTA
without `--delta-base-offset` enabled, so it's not a huge stretch to
do the same for cross-pack deltas even when `--delta-base-offset` is
enabled.
This would work, but would obviously result in larger-than-necessary
packs, as we in theory *could* represent these cross-pack deltas by
patching an existing OFS_DELTA. But it's not clear how much that
would matter in practice. I suspect it would have a lot to do with
how you pack your repository in the first place.
- Finally, we could patch OFS_DELTAs across packs in a similar fashion
as we do today for OFS_DELTAs within a single pack on either side of
a gap. This would result in the smallest packs of the three options
here, but implementing this would be more involved.
At minimum, you'd have to keep the reusable chunks list for all
reused packs, not just the one we're currently processing. And you'd
have to ensure that any bases which are a part of cross-pack deltas
appear before the delta. I think this is possible to do, but would
require assembling the reusable chunks list potentially in a
different order than they appear in the source packs.
For now, let's pursue the simplest approach and reject any cross-pack
deltas.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When performing a binary search over the objects in a MIDX's bitmap
(i.e. in pseudo-pack order), the reader reconstructs the pseudo-pack
ordering using a combination of (a) the preferred pack, (b) the pack's
lexical position in the MIDX based on pack names, and (c) the object
offset within the pack.
In order to perform this binary search, the reader must know the
identity of the preferred pack. This could be stored in the MIDX, but
isn't for historical reasons, mostly because it can easily be inferred
at read-time by looking at the object in the first bit position and
finding out which pack it was selected from in the MIDX, like so:
nth_midxed_pack_int_id(m, pack_pos_to_midx(m, 0));
In midx_to_pack_pos() which performs this binary search, we look up the
identity of the preferred pack before each search. This is relatively
quick, since it involves two table-driven lookups (one in the MIDX's
revindex for `pack_pos_to_midx()`, and another in the MIDX's object
table for `nth_midxed_pack_int_id()`).
But since the preferred pack does not change after the MIDX is written,
it is safe to cache this value on the MIDX itself.
Write a helper to do just that, and rewrite all of the existing
call-sites that care about the identity of the preferred pack in terms
of this new helper.
This will prepare us for a subsequent patch where we will need to binary
search through the MIDX's pseudo-pack order multiple times.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Further prepare for enabling verbatim pack-reuse over multiple packfiles
by changing the signature of reuse_partial_packfile_from_bitmap() to
populate an array of `struct bitmapped_pack *`'s instead of a pointer to
a single packfile.
Since the array we're filling out is sized dynamically[^1], add an
additional `size_t *` parameter which will hold the number of reusable
packs (equal to the number of elements in the array).
Note that since we still have not implemented true multi-pack reuse,
these changes aren't propagated out to the rest of the caller in
builtin/pack-objects.c.
In the interim state, we expect that the array has a single element, and
we use that element to fill out the static `reuse_packfile` variable
(which is a bog-standard `struct packed_git *`). Future commits will
continue to push this change further out through the pack-objects code.
[^1]: That is, even though we know the number of packs which are
candidates for pack-reuse, we do not know how many of those
candidates we can actually reuse.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The signature of `reuse_partial_packfile_from_bitmap()` currently takes
in a bitmap, as well as three output parameters (filled through
pointers, and passed as arguments), and also returns an integer result.
The output parameters are filled out with: (a) the packfile used for
pack-reuse, (b) the number of objects from that pack that we can reuse,
and (c) a bitmap indicating which objects we can reuse. The return value
is either -1 (when there are no objects to reuse), or 0 (when there is
at least one object to reuse).
Some of these parameters are redundant. Notably, we can infer from the
bitmap how many objects are reused by calling bitmap_popcount(). And we
can similar compute the return value based on that number as well.
As such, clean up the signature of this function to drop the "*entries"
parameter, as well as the int return value, since the single caller of
this function can infer these values themself.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When trying to assemble a pack with bitmaps using `--use-bitmap-index`,
`pack-objects` asks the pack-bitmap machinery for a bitmap which
indicates the set of objects we can "reuse" verbatim from on-disk.
This set is roughly comprised of: a prefix of objects in the bitmapped
pack (or preferred pack, in the case of a multi-pack reachability
bitmap), plus any other objects not included in the prefix, excluding
any deltas whose base we are not sending in the resulting pack.
The pack-bitmap machinery is responsible for computing this bitmap, and
does so with the following functions:
- reuse_partial_packfile_from_bitmap()
- try_partial_reuse()
In the existing implementation, the first function is responsible for
(a) marking the prefix of objects in the reusable pack, and then (b)
calling try_partial_reuse() on any remaining objects to ensure that they
are also reusable (and removing them from the bitmapped set if they are
not).
Likewise, the `try_partial_reuse()` function is responsible for checking
whether an isolated object (that is, an object from the bitmapped
pack/preferred pack not contained in the prefix from earlier) may be
reused, i.e. that it isn't a delta of an object that we are not sending
in the resulting pack.
These functions are based on two core assumptions, which we will unwind
in this and the following commits:
1. There is only a single pack from the bitmap which is eligible for
verbatim pack-reuse. For single-pack bitmaps, this is trivially the
bitmapped pack. For multi-pack bitmaps, this is (currently) the
MIDX's preferred pack.
2. The pack eligible for reuse has its first object in bit position 0,
and all objects from that pack follow in pack-order from that first
bit position.
In order to perform verbatim pack reuse over multiple packs, we must
unwind these two assumptions. Most notably, in order to reuse bits from
a given packfile, we need to know the first bit position occupied by
an object form that packfile. To propagate this information around, pass
a `struct bitmapped_pack *` anywhere we previously passed a `struct
packed_git *`, since the former contains the bitmap position we're
interested in (as well as a pointer to the latter).
As an additional step, factor out a sub-routine from the main
`reuse_partial_packfile_from_bitmap()` function, called
`reuse_partial_packfile_from_bitmap_1()`. This new function will be
responsible for figuring out which objects may be reused from a single
pack, and the existing function will dispatch multiple calls to its new
helper function for each reusable pack.
Consequently, `reuse_partial_packfile_from_bitmap()` will now maintain
an array of reusable packs instead of a single such pack. We currently
expect that array to have only a single element, so this awkward state
is short-lived. It will serve as useful scaffolding in subsequent
commits as we begin to work towards enabling multi-pack reuse.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `find_objects()` function creates an object_list for any tips of the
reachability query which do not have corresponding bitmaps.
The object_list is not used outside of `find_objects()`, but we never
free it with `object_list_free()`, resulting in a leak. Let's plug that
leak by calling `object_list_free()`, which results in t6113 becoming
leak-free.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git rev-list --unpacked --objects" failed to exclude packed
non-commit objects, which has been corrected.
* tb/rev-list-unpacked-fix:
pack-bitmap: drop --unpacked non-commit objects from results
list-objects: drop --unpacked non-commit objects from results
When performing revision queries with `--objects` and
`--use-bitmap-index`, the output may incorrectly contain objects which
are packed, even when the `--unpacked` option is given. This affects
traversals, but also other querying operations, like `--count`,
`--disk-usage`, etc.
Like in the previous commit, the fix is to exclude those objects from
the result set before they are shown to the user (or, in this case,
before the bitmap containing the result of the traversal is enumerated
and its objects listed).
This is performed by a new function in pack-bitmap.c, called
`filter_packed_objects_from_bitmap()`. Note that we do not have to
inspect individual bits in the result bitmap, since we know that the
first N (where N is the number of objects in the bitmap's pack/MIDX)
bits correspond to objects which packed by definition.
In other words, for an object to have a bitmap position (not in the
extended index), it must appear in either the bitmap's pack or one of
the packs in its MIDX.
This presents an appealing optimization to us, which is that we can
simply memset() the corresponding number of `eword_t`'s to zero,
provided that we handle any objects which spill into the next word (but
don't occupy all 64 bits of the word itself).
We only have to handle objects in the bitmap's extended index. These
objects may (or may not) appear in one or more pack(s). Since these
objects are known to not appear in either the bitmap's MIDX or pack,
they may be stored as loose, appear in other pack(s), or both.
Before returning a bitmap containing the result of the traversal back to
the caller, drop any bits from the extended index which appear in one or
more packs. This implements the correct behavior for rev-list operations
which use the bitmap index to compute their result.
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This is similar to the cases in c50dca2a18 (list-objects: mark unused
callback parameters, 2023-02-24), but was added after that commit.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Various offset computation in the code that accesses the packfiles
and other data in the object layer has been hardened against
arithmetic overflow, especially on 32-bit systems.
* tb/object-access-overflow-protection:
commit-graph.c: prevent overflow in `verify_commit_graph()`
commit-graph.c: prevent overflow in `write_commit_graph()`
commit-graph.c: prevent overflow in `merge_commit_graph()`
commit-graph.c: prevent overflow in `split_graph_merge_strategy()`
commit-graph.c: prevent overflow in `load_tree_for_commit()`
commit-graph.c: prevent overflow in `fill_commit_in_graph()`
commit-graph.c: prevent overflow in `fill_commit_graph_info()`
commit-graph.c: prevent overflow in `load_oid_from_graph()`
commit-graph.c: prevent overflow in add_graph_to_chain()
commit-graph.c: prevent overflow in `write_commit_graph_file()`
pack-bitmap.c: ensure that eindex lookups don't overflow
midx.c: prevent overflow in `fill_included_packs_batch()`
midx.c: prevent overflow in `write_midx_internal()`
midx.c: store `nr`, `alloc` variables as `size_t`'s
midx.c: prevent overflow in `nth_midxed_offset()`
midx.c: prevent overflow in `nth_midxed_object_oid()`
midx.c: use `size_t`'s for fanout nr and alloc
packfile.c: use checked arithmetic in `nth_packed_object_offset()`
packfile.c: prevent overflow in `load_idx()`
packfile.c: prevent overflow in `nth_packed_object_id()`
When a bitmap is used to answer some reachability query, it creates a
pseudo-bitmap called the "extended index" on top of any existing bitmaps
to store objects that are relevant to the query, but not mentioned in
the bitmap.
When looking up the ith object in the extended index in a bitmap, it is
common to write something like:
bitmap_get(result, i + bitmap_num_objects(bitmap_git))
, indicating that we want the ith object following all other objects
mentioned in the bitmap_git.
Since the type of `i` and the return type of `bitmap_num_objects()` are
both `uint32_t`s, But if there are either a large number of objects in
the bitmap, or a large number of objects in the extended index (or
both), this addition can overflow when the sum is greater than 2^32-1.
Having that large of a bitmap position is entirely acceptable, but we
need to ensure that the computed bitmap position for that object is
performed using 64-bits and doesn't overflow.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
alloc_nr, ALLOC_GROW, and ALLOC_GROW_BY are commonly used macros for
dynamic array allocation. Moving these macros to git-compat-util.h with
the other alloc macros focuses alloc.[ch] to allocation for Git objects
and additionally allows us to remove inclusions to alloc.h from files
that solely used the above macros.
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Header files cleanup.
* en/header-split-cache-h-part-3: (28 commits)
fsmonitor-ll.h: split this header out of fsmonitor.h
hash-ll, hashmap: move oidhash() to hash-ll
object-store-ll.h: split this header out of object-store.h
khash: name the structs that khash declares
merge-ll: rename from ll-merge
git-compat-util.h: remove unneccessary include of wildmatch.h
builtin.h: remove unneccessary includes
list-objects-filter-options.h: remove unneccessary include
diff.h: remove unnecessary include of oidset.h
repository: remove unnecessary include of path.h
log-tree: replace include of revision.h with simple forward declaration
cache.h: remove this no-longer-used header
read-cache*.h: move declarations for read-cache.c functions from cache.h
repository.h: move declaration of the_index from cache.h
merge.h: move declarations for merge.c from cache.h
diff.h: move declaration for global in diff.c from cache.h
preload-index.h: move declarations for preload-index.c from elsewhere
sparse-index.h: move declarations for sparse-index.c from cache.h
name-hash.h: move declarations for name-hash.c from cache.h
run-command.h: move declarations for run-command.c from cache.h
...
Gracefully deal with a stale MIDX file that lists a packfile that
no longer exists.
* tb/open-midx-bitmap-fallback:
pack-bitmap.c: gracefully degrade on failure to load MIDX'd pack
The object traversal using reachability bitmap done by
"pack-object" has been tweaked to take advantage of the fact that
using "boundary" commits as representative of all the uninteresting
ones can save quite a lot of object enumeration.
* tb/pack-bitmap-traversal-with-boundary:
pack-bitmap.c: use commit boundary during bitmap traversal
pack-bitmap.c: extract `fill_in_bitmap()`
object: add object_array initializer helper function
Junio C Hamano