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Now that it is safe to call git_hash_discard() even after finalizing it,
we can simplify our cleanup logic a bit. This is mostly undoing a few
bits of 64337aecde (csum-file: always finalize or discard hash,
2026-07-02):
- We no longer need a separate free_hashfile_memory() function for
finalize_hashfile(). It can just call free_hashfile(), which will
now discard (or not) the hash as appropriate.
- When f->skip_hash is set, we don't need to discard; we can rely on
free_hashfile() to do it.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We'd like to add more logic to git_hash_init(), but many callers skip it
and call algop->init_fn() directly. Let's make sure we're consistently
using the wrapper by adding a coccinelle rule.
Besides the coccinelle file itself, this is a purely mechanical
conversion based on the patch it generates. There should be no bare
init_fn() calls left (except for the one in the wrapper).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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* jk/hash-algo-leak-fixes:
hash: add platform-specific discard functions
hash: fix memory leak copying sha256 gcrypt handles
http: discard hash in dumb-http http_object_request
check_stream_oid(): discard hash on read error
patch-id: discard hash when done
csum-file: provide a function to release checkpoints
csum-file: always finalize or discard hash
hash: add discard primitive
csum-file: drop discard_hashfile()
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A hashfile_checkpoint struct is basically just a copy of the hash_ctx
state at a given point in the file. As such, it contains its own
git_hash_ctx which may (depending on the underlying hash implementation)
need to be discarded when we're done with it.
Let's add a "release" function which cleans up the hash context it
holds. I chose "release" here and not "discard" because you'd use this
to clean up every checkpoint, whether you used it or not. As opposed to
git_hash_discard(), which is needed only if you didn't call
git_hash_final().
There are only two callers which use hashfile_checkpoints, and we can
add release calls to both. When built with "SANITIZE=leak
OPENSSL_SHA1_UNSAFE=1", this makes both t1050 and t9300 leak-free.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When a hashfile struct is created, we always initialize the git_hash_ctx
inside it. We usually end up in hashfile_finalize(), which passes that
ctx to git_hash_final(), cleaning it up.
But a few code paths don't do so:
1. If we bail on the hashfile and call free_hashfile() directly rather
than finalizing.
2. If the skip_hash flag is set, the hashfile_finalize() call will
never call git_hash_final(). (You might think that we should just
avoid git_hash_init() entirely in this case, but the skip_hash flag
is set by the caller after the hashfile is initialized).
For most hash implementations this is OK, but for ones that allocate on
initialization it causes a memory leak. You can see many failures by
running:
make SANITIZE=leak OPENSSL_SHA1_UNSAFE=1 test
since OpenSSL >= 3.0 is such an allocating hash implementation (and
csum-file uses the "unsafe" algorithm variant).
We can solve this by calling git_hash_discard() as appropriate.
Note that free_hashfile() is used both directly by callers to abort
without finalizing, and by hashfile_finalize() to free memory. In the
latter case we _don't_ want to call git_hash_discard(), because we'll
already have either finalized or discarded it. So we'll push that to an
internal "free_memory" function, and keep free_hashfile() as the public
interface to abort a hashfile without finalizing.
This fix makes several scripts leak-free with the command above: t1600,
t1601, t2107, t7008, t9210, t9211.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Commit c3d034df16 (csum-file: introduce discard_hashfile(), 2024-07-25)
added a cleanup function that no longer has any callers. In that commit
we adjusted do_write_index() to use the new function. But a similar fix
occurred on a parallel branch, making free_hashfile() public, and the
merge resolution in 1b6b2bfae5 (Merge branch 'ps/leakfixes-part-4',
2024-08-23) took the free_hashfile() version.
So now we have two functions, discard_hashfile() and free_hashfile(),
and we only need one. Which one do we want to keep?
The only difference between them is that the discard variant also closes
the descriptors held in the struct. Let's look at the three callers:
1. In finalize_hashfile() we've either already closed the descriptors
(if the CSUM_CLOSE flag is passed) or the caller didn't want them
closed (if it didn't pass that flag). So we want the more limited
free_hashfile().
2. In object-file.c:flush_packfile_transaction() we close the
descriptor ourselves. So discard_hashfile() could save us a line of
code.
3. In do_write_index() we don't close the descriptor. This was the spot
for which c3d034df16 added the discard function in the first place,
but I'm skeptical that closing the descriptor here is the right
thing. It is true that we are done with the descriptor at this
point and closing it would be ideal. But we don't really own it!
The descriptor comes from a tempfile struct (as part of a lock) and
that tempfile will hold on to the descriptor and try to close it
when it is deleted. This might happen at the end of the program, in
which case the double-close is mostly harmless (we might
accidentally close some other open descriptor, but at that point
we're just closing and unlinking everything we can).
But in theory it could also cause subtle bugs. If do_write_index()
fails, we return the error up the stack and would eventually end up
in write_locked_index(). There we roll back the lock file on error,
which will close the descriptor. So now we get our double close,
and we might actually close something else that was opened in the
interim.
This is probably unlikely in practice (as soon as we see the error
we'd mostly be unwinding the stack, not opening new files). But it
highlights a potential problem with the discard_hashfile()
interface: the hashfile doesn't necessarily own that descriptor.
Note that I said "descriptors" plural above. Those callers all care
about the "fd" member of the struct. But discard_hashfile() also closes
check_fd. That is only used if the struct is initialized with
hashfd_check(), and neither of its two callers call either discard or
free (they always "finalize" instead). So closing it is irrelevant for
the current callers.
I think we're better off sticking with the simpler free_hashfile()
interface, and the handful of callers can decide how to handle the
descriptors themselves.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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index-pack and unpack-objects both read pack data from stdin through
a 4 KiB static buffer. In index-pack, each fill() flushes consumed
bytes to the pack file via write_or_die(), capping every write(2)
at 4 KiB. unpack-objects uses the same buffer pattern for reads.
On FUSE-backed filesystems every write(2) is a synchronous round
trip through the FUSE protocol (userspace -> kernel -> userspace ->
back), so the 4 KiB buffer turns a clone into many unnecessary tiny
writes with noticeable latency overhead.
Increase the buffer from 4 KiB to 128 KiB. Introduce a shared
DEFAULT_IO_BUFFER_SIZE constant in git-compat-util.h (next to
MAX_IO_SIZE) and use it in index-pack, unpack-objects, and the
hashfile layer in csum-file (which already used 128 KiB but
hardcoded the value).
Pack file writes to a FUSE filesystem with writeback caching
disabled during HTTPS clones of git/git (~293 MB pack):
74,958 -> 4,687 (94% fewer)
Wall-clock time of git clone over HTTPS onto a FUSE passthrough
filesystem with writeback caching disabled, 3 runs per variant:
vscode (~1.26 GB pack): 84.5s -> 75.7s avg (10% faster)
git/git (~306 MB pack): 22.6s -> 20.0s avg (11% faster)
Signed-off-by: Scott Bauersfeld <sbauersfeld@g.ucla.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Reduce system overhead "git upload-pack" spends on relaying "git
pack-objects" output to the "git fetch" running on the other end of
the connection.
* ps/upload-pack-buffer-more-writes:
builtin/pack-objects: reduce lock contention when writing packfile data
csum-file: drop `hashfd_throughput()`
csum-file: introduce `hashfd_ext()`
sideband: use writev(3p) to send pktlines
wrapper: introduce writev(3p) wrappers
compat/posix: introduce writev(3p) wrapper
upload-pack: reduce lock contention when writing packfile data
upload-pack: prefer flushing data over sending keepalive
upload-pack: adapt keepalives based on buffering
upload-pack: fix debug statement when flushing packfile data
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The `hashfd_throughput()` function is used by a single callsite in
git-pack-objects(1). In contrast to `hashfd()`, this function uses a
progress meter to measure throughput and a smaller buffer length so that
the progress meter can provide more granular metrics.
We're going to change that caller in the next commit to be a bit more
specific to packing objects. As such, `hashfd_throughput()` will be a
somewhat unfitting mechanism for any potential new callers.
Drop the function and replace it with a call to `hashfd_ext()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Introduce a new `hashfd_ext()` function that takes an options structure.
This function will replace `hashd_throughput()` in the next commit.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We want to call this code from Rust and ensure that the types are the
same for compatibility, which is easiest to do if the type is a fixed
size. Since unsigned int is 32 bits on all the platforms we care about,
define it as a uint32_t instead.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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There are multiple sites in "csum-file.c" where we use the global
`the_repository` variable, either explicitly or implicitly by using
`the_hash_algo`.
Refactor the code to stop using `the_repository` by adapting functions
to receive required data as parameters. Adapt callsites accordingly by
either using `the_repository->hash_algo`, or by using a context-provided
hash algorithm in case the subsystem already got rid of its dependency
on `the_repository`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Further code clean-up on the use of hash functions. Now the
context object knows what hash function it is working with.
* ps/hash-cleanup:
global: adapt callers to use generic hash context helpers
hash: provide generic wrappers to update hash contexts
hash: stop typedeffing the hash context
hash: convert hashing context to a structure
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The code paths to interact with zlib has been cleaned up in
preparation for building with zlib-ng.
* ps/zlib-ng:
ci: make "linux-musl" job use zlib-ng
ci: switch linux-musl to use Meson
compat/zlib: allow use of zlib-ng as backend
git-zlib: cast away potential constness of `next_in` pointer
compat/zlib: provide stubs for `deflateSetHeader()`
compat/zlib: provide `deflateBound()` shim centrally
git-compat-util: move include of "compat/zlib.h" into "git-zlib.h"
compat: introduce new "zlib.h" header
git-compat-util: drop `z_const` define
compat: drop `uncompress2()` compatibility shim
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Adapt callers to use generic hash context helpers instead of using the
hash algorithm to update them. This makes the callsites easier to reason
about and removes the possibility that the wrong hash algorithm is used
to update the hash context's state. And as a nice side effect this also
gets rid of a bunch of users of `the_hash_algo`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We generally avoid using `typedef` in the Git codebase. One exception
though is the `git_hash_ctx`, likely because it used to be a union
rather than a struct until the preceding commit refactored it. But now
that it is a normal `struct` there isn't really a need for a typedef
anymore.
Drop the typedef and adapt all callers accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We include "compat/zlib.h" in "git-compat-util.h", which is
unnecessarily broad given that we only have a small handful of files
that use the zlib library. Move the header into "git-zlib.h" instead and
adapt users of zlib to include that header.
One exception is the reftable library, as we don't want to use the
Git-specific wrapper of zlib there, so we include "compat/zlib.h"
instead. Furthermore, we move the include into "reftable/system.h" so
that users of the library other than Git can wire up zlib themselves.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In 106140a99f (builtin/fast-import: fix segfault with unsafe SHA1
backend, 2024-12-30) and 9218c0bfe1 (bulk-checkin: fix segfault with
unsafe SHA1 backend, 2024-12-30), we observed the effects of failing to
initialize a hashfile_checkpoint with the same hash function
implementation as is used by the hashfile it is used to checkpoint.
While both 106140a99f and 9218c0bfe1 work around the immediate crash,
changing the hash function implementation within the hashfile API to,
for example, the non-unsafe variant would re-introduce the crash. This
is a result of the tight coupling between initializing hashfiles and
hashfile_checkpoints.
Introduce and use a new function which ensures that both parts of a
hashfile and hashfile_checkpoint pair use the same hash function
implementation to avoid such crashes.
A few things worth noting:
- In the change to builtin/fast-import.c::stream_blob(), we can see
that by removing the explicit reference to
'the_hash_algo->unsafe_init_fn()', we are hardened against the
hashfile API changing away from the_hash_algo (or its unsafe
variant) in the future.
- The bulk-checkin code no longer needs to explicitly zero-initialize
the hashfile_checkpoint, since it is now done as a result of calling
'hashfile_checkpoint_init()'.
- Also in the bulk-checkin code, we add an additional call to
prepare_to_stream() outside of the main loop in order to initialize
'state->f' so we know which hash function implementation to use when
calling 'hashfile_checkpoint_init()'.
This is OK, since subsequent 'prepare_to_stream()' calls are noops.
However, we only need to call 'prepare_to_stream()' when we have the
HASH_WRITE_OBJECT bit set in our flags. Without that bit, calling
'prepare_to_stream()' does not assign 'state->f', so we have nothing
to initialize.
- Other uses of the 'checkpoint' in 'deflate_blob_to_pack()' are
appropriately guarded.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Instead of calling the unsafe_ hash function variants directly, make use
of the shared 'algop' pointer by initializing it to:
f->algop = unsafe_hash_algo(the_hash_algo);
, thus making all calls use the unsafe variants directly.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Perform a similar transformation as in the previous commit, but focused
instead on hashfile_checksum_valid(). This function does not work with a
hashfile structure itself, and instead validates the raw contents of a
file written using the hashfile API.
We'll want to be prepared for a similar change to this function in the
future, so prepare ourselves for that by extracting 'the_hash_algo' into
its own field for use within this function.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Throughout the hashfile API, we rely on a reference to 'the_hash_algo',
and call its _unsafe function variants directly.
Prepare for a future change where we may use a different 'git_hash_algo'
pointer (instead of just relying on 'the_hash_algo' throughout) by
making the 'git_hash_algo' pointer a member of the 'hashfile' structure
itself.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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On 32-bit platforms, ssize_t may be "int" while size_t may be
"unsigned int". At times we compare the number of bytes we read
stored in a ssize_t variable with "unsigned int", but that is done
after we check that we did not get an error return (which is
negative---and that is the whole reason why we used ssize_t and not
size_t), so these comparisons are safe.
But compilers may not realize that. Cast these to size_t to work
around the false positives. On platforms with size_t/ssize_t wider
than a normal int, this won't be an issue.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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Update hashwrite() and friends to use the unsafe_-variants of hashing
functions, calling for e.g., "the_hash_algo->unsafe_update_fn()" instead
of "the_hash_algo->update_fn()".
These callers only use the_hash_algo to produce a checksum, which we
depend on for data integrity, but not for cryptographic purposes, so
these callers are safe to use the unsafe (non-collision detecting) SHA-1
implementation.
To time this, I took a freshly packed copy of linux.git, and ran the
following with and without the OPENSSL_SHA1_UNSAFE=1 build-knob. Both
versions were compiled with -O3:
$ git for-each-ref --format='%(objectname)' refs/heads refs/tags >in
$ valgrind --tool=callgrind ~/src/git/git-pack-objects \
--revs --stdout --all-progress --use-bitmap-index <in >/dev/null
Without OPENSSL_SHA1_UNSAFE=1 (that is, using the collision-detecting
SHA-1 implementation for both cryptographic and non-cryptographic
purposes), we spend a significant amount of our instruction count in
hashwrite():
$ callgrind_annotate --inclusive=yes | grep hashwrite | head -n1
159,998,868,413 (79.42%) /home/ttaylorr/src/git/csum-file.c:hashwrite [/home/ttaylorr/src/git/git-pack-objects]
, and the resulting "clone" takes 19.219 seconds of wall clock time,
18.94 seconds of user time and 0.28 seconds of system time.
Compiling with OPENSSL_SHA1_UNSAFE=1, we spend ~60% fewer instructions
in hashwrite():
$ callgrind_annotate --inclusive=yes | grep hashwrite | head -n1
59,164,001,176 (58.79%) /home/ttaylorr/src/git/csum-file.c:hashwrite [/home/ttaylorr/src/git/git-pack-objects]
, and generate the resulting "clone" much faster, in only 11.597 seconds
of wall time, 11.37 seconds of user time, and 0.23 seconds of system
time, for a ~40% speed-up.
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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More leak fixes.
* ps/leakfixes-part-4: (22 commits)
builtin/diff: free symmetric diff members
diff: free state populated via options
builtin/log: fix leak when showing converted blob contents
userdiff: fix leaking memory for configured diff drivers
builtin/format-patch: fix various trivial memory leaks
diff: fix leak when parsing invalid ignore regex option
unpack-trees: clear index when not propagating it
sequencer: release todo list on error paths
merge-ort: unconditionally release attributes index
builtin/fast-export: plug leaking tag names
builtin/fast-export: fix leaking diff options
builtin/fast-import: plug trivial memory leaks
builtin/notes: fix leaking `struct notes_tree` when merging notes
builtin/rebase: fix leaking `commit.gpgsign` value
config: fix leaking comment character config
submodule-config: fix leaking name entry when traversing submodules
read-cache: fix leaking hashfile when writing index fails
bulk-checkin: fix leaking state TODO
object-name: fix leaking symlink paths in object context
object-file: fix memory leak when reading corrupted headers
...
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When flushing a bulk-checking to disk we also reset the `struct
bulk_checkin_packfile` state. But while we free some of its members,
others aren't being free'd, leading to memory leaks:
- The temporary packfile name is not getting freed.
- The `struct hashfile` only gets freed in case we end up calling
`finalize_hashfile()`. There are code paths though where that is not
the case, namely when nothing has been written. For this, we need to
make `free_hashfile()` public.
Fix those leaks.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The hashfile API is used to write out a "hashfile", which has a
final checksum (typically SHA-1) at the end. An in-core hashfile
structure has up to two file descriptors and a few buffers that can
only be freed by calling a helper function that is private to the
csum-file implementation.
The usual flow of a user of the API is to first open a file
descriptor for writing, obtain a hashfile associated with that write
file descriptor by calling either hashfd() or hashfd_check(), call
hashwrite() number of times to write data to the file, and then call
finalize_hashfile(), which appends th checksum to the end of the
file, closes file descriptors and releases associated buffers.
But what if a caller finds some error after calling hashfd() to
start the process and/or hashwrite() to send some data to the file,
and wants to abort the operation? The underlying file descriptor is
often managed by the tempfile API, so aborting will clean the file
out of the filesystem, but the resources associated with the in-core
hashfile structure is lost.
Introduce discard_hashfile() API function to allow them to release
the resources held by a hashfile structure the callers want to
dispose of, and use that in read-cache.c:do_write_index(), which is
a central place that writes the index file.
Mark t2107 as leak-free, as this leak in "update-index --cacheinfo"
test that deliberately makes it fail is now plugged.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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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>
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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>
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Fix-up new-ish code to support OpenSSL EVP API.
* ew/hash-with-openssl-evp:
treewide: fix various bugs w/ OpenSSL 3+ EVP API
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The OpenSSL 3+ EVP API for SHA-* cannot support our prior use cases
supported by other SHA-* implementations. It has the following
differences:
1. ->init_fn is required before all use
2. struct assignments don't work and requires ->clone_fn
3. can't support ->update_fn after ->final_*fn
While fixing cases 1 and 2 is merely the matter of calling ->init_fn and
->clone_fn as appropriate, fixing case 3 requires calling ->final_*fn on
a temporary context that's cloned from the primary context.
Reported-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/ZPCL11k38PXTkFga@debian.me/
Helped-by: brian m. carlson <sandals@crustytoothpaste.net>
Fixes: 3e440ea0aba0 ("sha256: avoid functions deprecated in OpenSSL 3+")
Fixes: bda9c12073e7 ("avoid SHA-1 functions deprecated in OpenSSL 3+")
Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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hash.h depends upon and includes repository.h, due to the definition and
use of the_hash_algo (defined as the_repository->hash_algo). However,
most headers trying to include hash.h are only interested in the layout
of the structs like object_id. Move the parts of hash.h that do not
depend upon repository.h into a new file hash-ll.h (the "low level"
parts of hash.h), and adjust other files to use this new header where
the convenience inline functions aren't needed.
This allows hash.h and object.h to be fairly small, minimal headers. It
also exposes a lot of hidden dependencies on both path.h (which was
brought in by repository.h) and repository.h (which was previously
implicitly brought in by object.h), so also adjust other files to be
more explicit about what they depend upon.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The hashfile API is useful for generating files that include a trailing
hash of the file's contents up to that point. Using such a hash is
helpful for verifying the file for corruption-at-rest, such as a faulty
drive causing flipped bits.
Git's index file includes this trailing hash, so it uses a 'struct
hashfile' to handle the I/O to the file. This was very convenient to
allow using the hashfile methods during these operations.
However, hashing the file contents during write comes at a performance
penalty. It's slower to hash the bytes on their way to the disk than
without that step. This problem is made worse by the replacement of
hardware-accelerated SHA1 computations with the software-based sha1dc
computation.
This write cost is significant, and the checksum capability is likely
not worth that cost for such a short-lived file. The index is rewritten
frequently and the only time the checksum is checked is during 'git
fsck'. Thus, it would be helpful to allow a user to opt-out of the hash
computation.
We first need to allow Git to opt-out of the hash computation in the
hashfile API. The buffered writes of the API are still helpful, so it
makes sense to make the change here.
Introduce a new 'skip_hash' option to 'struct hashfile'. When set, the
update_fn and final_fn members of the_hash_algo are skipped. When
finalizing the hashfile, the trailing hash is replaced with the null
hash.
This use of a trailing null hash would be desireable in either case,
since we do not want to special case a file format to have a different
length depending on whether it was hashed or not. When the final bytes
of a file are all zero, we can infer that it was written without
hashing, and thus that verification is not available as a check for file
consistency. This also means that we could easily toggle hashing for any
file format we desire.
A version of this patch has existed in the microsoft/git fork since
2017 [1] (the linked commit was rebased in 2018, but the original dates
back to January 2017). Here, the change to make the index use this fast
path is delayed until a later change.
[1] https://github.com/microsoft/git/commit/21fed2d91410f45d85279467f21d717a2db45201
Co-authored-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This commit introduces the infrastructure for the core.fsync
configuration knob. The repository components we want to sync
are identified by flags so that we can turn on or off syncing
for specific components.
If core.fsyncObjectFiles is set and the core.fsync configuration
also includes FSYNC_COMPONENT_LOOSE_OBJECT, we will fsync any
loose objects. This picks the strictest data integrity behavior
if core.fsync and core.fsyncObjectFiles are set to conflicting values.
This change introduces the currently unused fsync_component
helper, which will be used by a later patch that adds fsyncing to
the refs backend.
Actual configuration and documentation of the fsync components
list are in other patches in the series to separate review of
the underlying mechanism from the policy of how it's configured.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add and apply a semantic patch for using xopen() instead of calling
open(2) and die() or die_errno() explicitly. This makes the error
messages more consistent and shortens the code.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When rebuilding the multi-pack index file reusing an existing one,
we used to blindly trust the existing file and ended up carrying
corrupted data into the updated file, which has been corrected.
* tb/midx-use-checksum:
midx: report checksum mismatches during 'verify'
midx: don't reuse corrupt MIDXs when writing
commit-graph: rewrite to use checksum_valid()
csum-file: introduce checksum_valid()
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Introduce a new function which checks the validity of a file's trailing
checksum. This is similar to hashfd_check(), but different since it is
intended to be used by callers who aren't writing the same data (like
`git index-pack --verify`), but who instead want to validate the
integrity of data that they are reading.
Rewrite the first of two callers which could benefit from this new
function in pack-check.c. Subsequent callers will be added in the
following patches.
Helped-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>
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The hashfile API uses a hard-coded buffer size of 8KB and has ever since
it was introduced in c38138c (git-pack-objects: write the pack files
with a SHA1 csum, 2005-06-26). It performs a similar function to the
hashing buffers in read-cache.c, but that code was updated from 8KB to
128KB in f279894 (read-cache: make the index write buffer size 128K,
2021-02-18). The justification there was that do_write_index() improves
from 1.02s to 0.72s. Since our end goal is to have the index writing
code use the hashfile API, we need to unify this buffer size to avoid a
performance regression.
There is a buffer, 'check_buffer', that is used to verify the check_fd
file descriptor. When this buffer increases to 128K to fit the data
being flushed, it causes the stack to overflow the limits placed in the
test suite. To avoid issues with stack size, move both 'buffer' and
'check_buffer' to be heap pointers within 'struct hashfile'. The
'check_buffer' member is left as NULL unless check_fd is set in
hashfd_check(). Both buffers are cleared as part of finalize_hashfile()
which also frees the full structure.
Since these buffers are now on the heap, we can adjust their size based
on the needs of the consumer. In particular, callers to
hashfd_throughput() are expecting to report progress indicators as the
buffer flushes. These callers would prefer the smaller 8k buffer to
avoid large delays between updates, especially for users with slower
networks. When the progress indicator is not used, the larger buffer is
preferrable.
By adding a new trace2 region in the chunk-format API, we can see that
the writing portion of 'git multi-pack-index write' lowers from ~1.49s
to ~1.47s on a Linux machine. These effects may be more pronounced or
diminished on other filesystems. The end-to-end timing is too noisy to
have a definitive change either way.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The flush() logic in csum-file.c was introduced originally by c38138c
(git-pack-objects: write the pack files with a SHA1 csum, 2005-06-26)
and a portion of the logic performs similar utility to write_in_full()
in wrapper.c. The history of write_in_full() is full of moves and
renames, but was originally introduced by 7230e6d (Add write_or_die(), a
helper function, 2006-08-21).
The point of these sections of code are to flush a write buffer using
xwrite() and report errors in the case of disk space issues or other
generic input/output errors. The logic in flush() can interpret the
output of write_in_full() to provide the correct error messages to
users.
The logic in the hashfile API has an additional set of logic to augment
the progress indicator between calls to xwrite(). This was introduced by
2a128d6 (add throughput display to git-push, 2007-10-30). It seems that
since the hashfile's buffer is only 8KB, these additional progress
indicators might not be incredibly necessary. Instead, update the
progress only when write_in_full() complete.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The hashwrite() method takes an input buffer and updates a hashfile's
hash function while writing the data to a file. To avoid overuse of
flushes, the hashfile has an internal buffer and most writes will use
memcpy() to transfer data from the input 'buf' to the hashfile's buffer
of size 8 * 1024 bytes.
Logic introduced by a8032d12 (sha1write: don't copy full sized buffers,
2008-09-02) reduces the number of memcpy() calls when the input buffer
is sufficiently longer than the hashfile's buffer, causing nr to be the
length of the full buffer. In these cases, the input buffer is used
directly in chunks equal to the hashfile's buffer size.
This method caught my attention while investigating some performance
issues, but it turns out that these performance issues were noise within
the variance of the experiment.
However, during this investigation, I inspected hashwrite() and
misunderstood it, even after looking closely and trying to make it
faster. This change simply reorganizes some parts of the loop within
hashwrite() to make it clear that each batch either uses memcpy() to the
hashfile's buffer or writes directly from the input buffer. The previous
code relied on indirection through local variables and essentially
inlined the implementation of hashflush() to reduce lines of code.
Helped-by: Jeff King <peff@peff.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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For all of our SHA-1 implementations and most of our SHA-256
implementations, the hash context we use is a real struct. For these
implementations, it's possible to copy a hash context by making a copy
of the struct.
However, for our libgcrypt implementation, our hash context is a
pointer. Consequently, copying it does not lead to an independent hash
context like we intended.
Fortunately, however, libgcrypt provides us with a handy function to
copy hash contexts. Let's add a cloning function to the hash algorithm
API, and use it in the one place we need to make a hash context copy.
With this change, our libgcrypt SHA-256 implementation is fully
functional with all of our other hash implementations.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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If we want to use a hashfile on the temporary file for a lockfile, then
we need finalize_hashfile() to fully write the trailing hash but also keep
the file descriptor open.
Do this by adding a new CSUM_HASH_IN_STREAM flag along with a functional
change that checks this flag before writing the checksum to the stream.
This differs from previous behavior since it would be written if either
CSUM_CLOSE or CSUM_FSYNC is provided.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The hashclose() method behaves very differently depending on the flags
parameter. In particular, the file descriptor is not always closed.
Perform a simple rename of "hashclose()" to "finalize_hashfile()" in
preparation for functional changes.
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Convert several direct uses of SHA-1 to use the_hash_algo instead.
Convert one use of the constant 20 as well.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Rename struct sha1file to struct hashfile, along with all of its related
functions.
The transformation in this commit was made by global search-and-replace.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Comparing the result of read_in_full() using less-than is
potentially dangerous, as a negative return value may be
converted to an unsigned type and be considered a success.
This is discussed further in 561598cfcf (read_pack_header:
handle signed/unsigned comparison in read result,
2017-09-13).
Each of these instances is actually fine in practice:
- in get-tar-commit-id, the HEADERSIZE macro expands to a
signed integer. If it were switched to an unsigned type
(e.g., a size_t), then it would be a bug.
- the other two callers check for a short read only after
handling a negative return separately. This is a fine
practice, but we'd prefer to model "!=" as a general
rule.
So all of these cases can be considered cleanups and not
actual bugfixes.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Right now we return a NULL "struct sha1file" if we encounter
an error. However, the sole caller (write_idx_file) does not
check the return value, and will segfault if we hit this
case.
One option would be to handle the error in the caller.
However, there's really nothing for it to do but die. This
code path is hit during "git index-pack --verify"; after we
verify the packfile, we check that the ".idx" we would
generate from it is byte-wise identical to what is on disk.
We hit the error (and segfault) if we can't open the .idx
file (a likely cause of this is that somebody else ran "git
repack -ad" while we were verifying). Since we can't
complete the requested verification, we really have no
choice but to die.
Furthermore, the rest of the sha1fd_* functions simply die
on errors. So if were to open the file successfully, for
example, and then hit a read error, sha1write would call
die() for us. So pushing the die() down into sha1fd_check
keeps the interface consistent.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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