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Same as the "reftable" backend that we have adapted in the preceding
commit to use batched refname availability checks we can also do so for
the "files" backend. Things are a bit more intricate here though, as we
call `refs_verify_refname_available()` in a set of different contexts:
1. `lock_raw_ref()` when it hits either EEXISTS or EISDIR when creating
a new reference, mostly to create a nice, user-readable error
message. This is nothing we have to care about too much, as we only
hit this code path at most once when we hit a conflict.
2. `lock_raw_ref()` when it _could_ create the lockfile to check
whether it is conflicting with any packed refs. In the general case,
this code path will be hit once for every (successful) reference
update.
3. `lock_ref_oid_basic()`, but it is only executed when copying or
renaming references or when expiring reflogs. It will thus not be
called in contexts where we have many references queued up.
4. `refs_refname_ref_available()`, but again only when copying or
renaming references. It is thus not interesting due to the same
reason as the previous case.
5. `files_transaction_finish_initial()`, which is only executed when
creating a new repository or migrating references.
So out of these, only (2) and (5) are viable candidates to use the
batched checks.
Adapt `lock_raw_ref()` accordingly by queueing up reference names that
need to be checked for availability and then checking them after we have
processed all updates. This check is done before we (optionally) lock
the `packed-refs` file, which is somewhat flawed because it means that
the `packed-refs` could still change after the availability check and
thus create an undetected conflict. But unconditionally locking the file
would change semantics that users are likely to rely on, so we keep the
current locking sequence intact, even if it's suboptmial.
The refactoring of `files_transaction_finish_initial()` will be done 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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Refactor the "reftable" backend to batch the availability check for
refnames. This does not yet have an effect on performance as
`refs_verify_refnames_available()` effectively still performs the
availability check for each refname individually. But this will be
optimized in subsequent commits, where we learn to optimize some parts
of the logic when checking multiple refnames for availability.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `null_oid()` function returns the object ID that only consists of
zeroes. Naturally, this ID also depends on the hash algorithm used, as
the number of zeroes is different between SHA1 and SHA256. Consequently,
the function returns the hash-algorithm-specific null object ID.
This is currently done by depending on `the_hash_algo`, which implicitly
makes us depend on `the_repository`. Refactor the function to instead
pass in the hash algorithm for which we want to retrieve the null object
ID. Adapt callsites accordingly by passing in `the_repository`, thus
bubbling up the dependency on that global variable by one layer.
There are a couple of trivial exceptions for subsystems that already got
rid of `the_repository`. These subsystems instead use the repository
that is available via the calling context:
- "builtin/grep.c"
- "grep.c"
- "refs/debug.c"
There are also two non-trivial exceptions:
- "diff-no-index.c": Here we know that we may not have a repository
initialized at all, so we cannot rely on `the_repository`. Instead,
we adapt `diff_no_index()` to get a `struct git_hash_algo` as
parameter. The only caller is located in "builtin/diff.c", where we
know to call `repo_set_hash_algo()` in case we're running outside of
a Git repository. Consequently, it is fine to continue passing
`the_repository->hash_algo` even in this case.
- "builtin/ls-files.c": There is an in-flight patch series that drops
`USE_THE_REPOSITORY_VARIABLE` in this file, which causes a semantic
conflict because we use `null_oid()` in `show_submodule()`. The
value is passed to `repo_submodule_init()`, which may use the object
ID to resolve a tree-ish in the superproject from which we want to
read the submodule config. As such, the object ID should refer to an
object in the superproject, and consequently we need to use its hash
algorithm.
This means that we could in theory just not bother about this edge
case at all and just use `the_repository` in "diff-no-index.c". But
doing so would feel misdesigned.
Remove the `USE_THE_REPOSITORY_VARIABLE` preprocessor define in
"hash.c".
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The path.[ch] API takes an explicit repository parameter passed
throughout the callchain, instead of relying on the_repository
singleton instance.
* ps/path-sans-the-repository:
path: adjust last remaining users of `the_repository`
environment: move access to "core.sharedRepository" into repo settings
environment: move access to "core.hooksPath" into repo settings
repo-settings: introduce function to clear struct
path: drop `git_path()` in favor of `repo_git_path()`
rerere: let `rerere_path()` write paths into a caller-provided buffer
path: drop `git_common_path()` in favor of `repo_common_path()`
worktree: return allocated string from `get_worktree_git_dir()`
path: drop `git_path_buf()` in favor of `repo_git_path_replace()`
path: drop `git_pathdup()` in favor of `repo_git_path()`
path: drop unused `strbuf_git_path()` function
path: refactor `repo_submodule_path()` family of functions
submodule: refactor `submodule_to_gitdir()` to accept a repo
path: refactor `repo_worktree_path()` family of functions
path: refactor `repo_git_path()` family of functions
path: refactor `repo_common_path()` family of functions
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With the preceding refactorings we now only have a couple of implicit
users of `the_repository` left in the "path" subsystem, all of which
depend on global state via `calc_shared_perm()`. Make the dependency on
`the_repository` explicit by passing the repo as a parameter instead and
adjust callers accordingly.
Note that this change bubbles up into a couple of subsystems that were
previously declared as free from `the_repository`. Instead of marking
all of them as `the_repository`-dependent again, we instead use the
repository that is available in the calling context. There are three
exceptions though with "copy.c", "pack-write.c" and "tempfile.c".
Adjusting these would require us to adapt callsites all over the place,
so this is left for a future iteration.
Mark "path.c" as free from `the_repository`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When there is a "sorted" trait in the header of the "packed-refs" file,
it means that each entry is sorted increasingly by comparing the
refname. We should add checks to verify whether the "packed-refs" is
sorted in this case.
Update the "packed_fsck_ref_header" to know whether there is a "sorted"
trail in the header. It may seem that we could record all refnames
during the parsing process and then compare later. However, this is not
a good design due to the following reasons:
1. Because we need to store the state across the whole checking
lifetime, we would consume a lot of memory if there are many entries
in the "packed-refs" file.
2. We cannot reuse the existing compare function "cmp_packed_ref_records"
which cause repetition.
Because "cmp_packed_ref_records" needs an extra parameter "struct
snaphost", extract the common part into a new function
"cmp_packed_ref_records" to reuse this function to compare.
Then, create a new function "packed_fsck_ref_sorted" to parse the file
again and user the new fsck message "packedRefUnsorted(ERROR)" to report
to the user if the file is not sorted.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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"packed-backend.c::next_record" will parse the ref entry to check the
consistency. This function has already checked the following things:
1. Parse the main line of the ref entry to inspect whether the oid is
not correct. Then, check whether the next character is oid. Then
check the refname.
2. If the next line starts with '^', it would continue to parse the
peeled oid and check whether the last character is '\n'.
As we decide to implement the ref consistency check for "packed-refs",
let's port these two checks and update the test to exercise the code.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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"packed-backend.c::next_record" will use "check_refname_format" to check
the consistency of the refname. If it is not OK, the program will die.
However, it is reported in [1], we cannot catch some corruption. But we
already have the code path and we must miss out something.
We use the following code to get the refname:
strbuf_add(&iter->refname_buf, p, eol - p);
iter->base.refname = iter->refname_buf.buf
In the above code, `p` is the start pointer of the refname and `eol` is
the next newline pointer. We calculate the length of the refname by
subtracting the two pointers. Then we add the memory range between `p`
and `eol` to get the refname.
However, if there are some NUL characters in the memory range between `p`
and `eol`, we will see the refname as a valid ref name as long as the
memory range between `p` and first occurred NUL character is valid.
In order to catch above corruption, create a new function
"refname_contains_nul" by searching the first NUL character. If it is
not at the end of the string, there must be some NUL characters in the
refname.
Use this function in "next_record" function to die the program if
"refname_contains_nul" returns true.
[1] https://lore.kernel.org/git/6cfee0e4-3285-4f18-91ff-d097da9de737@rd10.de/
Reported-by: R. Diez <rdiez-temp3@rd10.de>
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In "packed-backend.c::create_snapshot", if there is a header (the line
which starts with '#'), we will check whether the line starts with "#
pack-refs with: ". However, we need to consider other situations and
discuss whether we need to add checks.
1. If the header does not exist, we should not report an error to the
user. This is because in older Git version, we never write header in
the "packed-refs" file. Also, we do allow no header in "packed-refs"
in runtime.
2. If the header content does not start with "# packed-ref with: ", we
should report an error just like what "create_snapshot" does. So,
create a new fsck message "badPackedRefHeader(ERROR)" for this.
3. If the header content is not the same as the constant string
"PACKED_REFS_HEADER". This is expected because we make it extensible
intentionally and runtime "create_snapshot" won't complain about
unknown traits. In order to align with the runtime behavior. There is
no need to report.
As we have analyzed, we only need to check the case 2 in the above. In
order to do this, use "open_nofollow" function to get the file
descriptor and then read the "packed-refs" file via "strbuf_read". Like
what "create_snapshot" and other functions do, we could split the line
by finding the next newline in the buffer. When we cannot find a
newline, we could report an error.
So, create a function "packed_fsck_ref_next_line" to find the next
newline and if there is no such newline, use
"packedRefEntryNotTerminated(ERROR)" to report an error to the user.
Then, parse the first line to apply the checks. Update the test to
exercise the code.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We always write a space after "# pack-refs with:" but we don't align
with this rule in the "create_snapshot" method where we would check
whether header starts with "# pack-refs with:". It might seem that we
should undoubtedly tighten this rule, however, we don't have any
technical documentation about this and there is a possibility that we
would break the compatibility for other third-party libraries.
By investigating influential third-party libraries, we could conclude
how these libraries handle the header of "packed-refs" file:
1. libgit2 is fine and always writes the space. It also expects the
whitespace to exist.
2. JGit does not expect th header to have a trailing space, but expects
the "peeled" capability to have a leading space, which is mostly
equivalent because that capability is typically the first one we
write. It always writes the space.
3. gitoxide expects the space t exist and writes it.
4. go-git doesn't create the header by default.
As many third-party libraries expect a single space after "# pack-refs
with:", if we forget to write the space after the colon,
"create_snapshot" won't catch this. And we would break other
re-implementations. So, we'd better tighten the rule by checking whether
the header starts with "# pack-refs with: ".
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Although "git-fsck(1)" and "packed-backend.c" will check some
consistency and correctness of "packed-refs" file, they never check the
filetype of the "packed-refs". Let's verify that the "packed-refs" has
the expected filetype, confirming it is created by "git pack-refs"
command.
We could use "open_nofollow" wrapper to open the raw "packed-refs" file.
If the returned "fd" value is less than 0, we could check whether the
"errno" is "ELOOP" to report an error to the user. And then we use
"fstat" to check whether the "packed-refs" file is a regular file.
Reuse "FSCK_MSG_BAD_REF_FILETYPE" fsck message id to report the error to
the user if "packed-refs" is not a regular file.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Code clean-up.
* kn/reflog-migration-fix-followup:
reftable: prevent 'update_index' changes after adding records
refs: use 'uint64_t' for 'ref_update.index'
refs: mark `ref_transaction_update_reflog()` as static
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Fix bugs in an earlier attempt to fix "git refs migration".
* kn/reflog-migration-fix-fix:
refs/reftable: fix uninitialized memory access of `max_index`
reftable: write correct max_update_index to header
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reflog entries for symbolic ref updates were broken, which has been
corrected.
* kn/reflog-symref-fix:
refs: fix creation of reflog entries for symrefs
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When migrating reflogs between reference backends, maintaining the
original order of the reflog entries is crucial. To achieve this, an
`index` field is stored within the `ref_update` struct that encodes the
relative order of reflog entries. This field is used by the reftable
backend as update index for the respective reflog entries to maintain
that ordering.
These update indices must be respected when writing table headers, which
encode the minimum and maximum update index of contained records in the
header and footer. This logic was added in commit bc67b4ab5f (reftable:
write correct max_update_index to header, 2025-01-15), which started to
use `reftable_writer_set_limits()` to propagate the mininum and maximum
update index of all records contained in a ref transaction.
However, we only set the maximum update index for the first transaction
argument, even though there can be multiple such arguments. This is the
case when we write to multiple stacks in a single transaction, e.g. when
updating references in two different worktrees at once. Consequently,
the update index for all but the first argument remain uninitialized,
which may cause undefined behaviour.
Fix this by moving the assignment of the maximum update index in
`reftable_be_transaction_finish()` inside the loop, which ensures that
all elements of the array are correctly initialized.
Furthermore, initialize the `max_index` field to 0 when queueing a new
transaction argument. This is not strictly necessary, as all elements of
`write_transaction_table_arg.max_index` are now assigned correctly.
However, this initialization is added for consistency and to safeguard
against potential future changes that might inadvertently introduce
uninitialized memory access.
Reported-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The commit 297c09eabb (refs: allow multiple reflog entries for the
same refname, 2024-12-16) added logic to exit early in
`lock_ref_for_update()` after obtaining the required lock. This was
added as a performance optimization on a false assumption that no
further processing was required for reflog-only updates.
However the assumption was wrong. For a symref's reflog entry, the
update needs to be populated with the old_oid value, but the early
exit skipped this necessary step.
This caused a bug in Git 2.48 in the files backend where target
references of symrefs being updated would create a corrupted reflog
entry for the symref since the old_oid is not populated.
Everything the early exit skipped in the code path is necessary for
both regular and symbolic ref, so eliminate the mistaken
optimization, and also add a test to ensure that such an issue
doesn't arise in the future.
Reported-by: Nika Layzell <nika@thelayzells.com>
Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The function `reftable_writer_set_limits()` allows updating the
'min_update_index' and 'max_update_index' of a reftable writer. These
values are written to both the writer's header and footer.
Since the header is written during the first block write, any subsequent
changes to the update index would create a mismatch between the header
and footer values. The footer would contain the newer values while the
header retained the original ones.
To protect against this bug, prevent callers from updating these values
after any record is written. To do this, modify the function to return
an error whenever the limits are modified after any record adds. Check
for record adds within `reftable_writer_set_limits()` by checking the
`last_key` and `next` variable. The former is updated after each record
added, but is reset at certain points. The latter is set after writing
the first block.
Modify all callers of the function to anticipate a return type and
handle it accordingly. Add a unit test to also ensure the function
returns the error as expected.
Helped-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The 'ref_update.index' variable is used to store an index for a given
reference update. This index is used to order the updates in a
predetermined order, while the default ordering is alphabetical as per
the refname.
For large repositories with millions of references, it should be safer
to use 'uint64_t'. Let's do that. This also is applied for all other
code sections where we store 'index' and pass it around.
Reported-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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* kn/reflog-migration-fix:
reftable: write correct max_update_index to header
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In 297c09eabb (refs: allow multiple reflog entries for the same refname,
2024-12-16), the reftable backend learned to handle multiple reflog
entries within the same transaction. This was done modifying the
`update_index` for reflogs with multiple indices. During writing the
logs, the `max_update_index` of the writer was modified to ensure the
limits were raised to the modified `update_index`s.
However, since ref entries are written before the modification to the
`max_update_index`, if there are multiple blocks to be written, the
reftable backend writes the header with the old `max_update_index`. When
all logs are finally written, the footer will be written with the new
`min_update_index`. This causes a mismatch between the header and the
footer and causes the reftable file to be corrupted. The existing tests
only spawn a single block and since headers are lazily written with the
first block, the tests didn't capture this bug.
To fix the issue, the appropriate `max_update_index` limit must be set
even before the first block is written. Add a `max_index` field to the
transaction which holds the `max_index` within all its updates, then
propagate this value to the reftable backend, wherein this is used to
the set the `max_update_index` correctly.
Add a test which creates a few thousand reference updates with multiple
reflog entries, which should trigger the bug.
Reported-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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"git refs migrate" learned to also migrate the reflog data across
backends.
* kn/reflog-migration:
refs: mark invalid refname message for translation
refs: add support for migrating reflogs
refs: allow multiple reflog entries for the same refname
refs: introduce the `ref_transaction_update_reflog` function
refs: add `committer_info` to `ref_transaction_add_update()`
refs: extract out refname verification in transactions
refs/files: add count field to ref_lock
refs: add `index` field to `struct ref_udpate`
refs: include committer info in `ref_update` struct
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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
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When "git fetch $remote" notices that refs/remotes/$remote/HEAD is
missing and discovers what branch the other side points with its
HEAD, refs/remotes/$remote/HEAD is updated to point to it.
* bf/set-head-symref:
fetch set_head: handle mirrored bare repositories
fetch: set remote/HEAD if it does not exist
refs: add create_only option to refs_update_symref_extended
refs: add TRANSACTION_CREATE_EXISTS error
remote set-head: better output for --auto
remote set-head: refactor for readability
refs: atomically record overwritten ref in update_symref
refs: standardize output of refs_read_symbolic_ref
t/t5505-remote: test failure of set-head
t/t5505-remote: set default branch to main
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The reference transaction only allows a single update for a given
reference to avoid conflicts. This, however, isn't an issue for reflogs.
There are no conflicts to be resolved in reflogs and when migrating
reflogs between backends we'd have multiple reflog entries for the same
refname.
So allow multiple reflog updates within a single transaction. Also the
reflog creation logic isn't exposed to the end user. While this might
change in the future, currently, this reduces the scope of issues to
think about.
In the reftable backend, the writer sorts all updates based on the
update_index before writing to the block. When there are multiple
reflogs for a given refname, it is essential that the order of the
reflogs is maintained. So add the `index` value to the `update_index`.
The `index` field is only set when multiple reflog entries for a given
refname are added and as such in most scenarios the old behavior
remains.
This is required to add reflog migration support to `git refs migrate`.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Introduce a new function `ref_transaction_update_reflog`, for clients to
add a reflog update to a transaction. While the existing function
`ref_transaction_update` also allows clients to add a reflog entry, this
function does a few things more, It:
- Enforces that only a reflog entry is added and does not update the
ref itself.
- Allows the users to also provide the committer information. This
means clients can add reflog entries with custom committer
information.
The `transaction_refname_valid()` function also modifies the error
message selectively based on the type of the update. This change also
affects reflog updates which go through `ref_transaction_update()`.
A follow up commit will utilize this function to add reflog support to
`git refs migrate`.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The `ref_transaction_add_update()` creates the `ref_update` struct. To
facilitate addition of reflogs in the next commit, the function needs to
accommodate setting the `committer_info` field in the struct. So modify
the function to also take `committer_info` as an argument and set it
accordingly.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When refs are updated in the files-backend, a lock is obtained for the
corresponding file path. This is the case even for reflogs, i.e. a lock
is obtained on the reference path instead of the reflog path. This
works, since generally, reflogs are updated alongside the ref.
The upcoming patches will add support for reflog updates in ref
transaction. This means, in a particular transaction we want to have ref
updates and reflog updates. For a given ref in a given transaction there
can be at most one update. But we can theoretically have multiple reflog
updates for a given ref in a given transaction. A great example of this
would be when migrating reflogs from one backend to another. There we
would batch all the reflog updates for a given reference in a single
transaction.
The current flow does not support this, because currently refs & reflogs
are treated as a single entity and capture the lock together. To
separate this, add a count field to ref_lock. With this, multiple
updates can hold onto a single ref_lock and the lock will only be
released when all of them release the lock.
This patch only adds the `count` field to `ref_lock` and adds the logic
to increment and decrement the lock. In a follow up commit, we'll
separate the reflog update logic from ref updates and utilize this
functionality.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The reftable backend, sorts its updates by refname before applying them,
this ensures that the references are stored sorted. When migrating
reflogs from one backend to another, the order of the reflogs must be
maintained. Add a new `index` field to the `ref_update` struct to
facilitate this.
This field is used in the reftable backend's sort comparison function
`transaction_update_cmp`, to ensure that indexed fields maintain their
order.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The reference backends obtain the committer information from
`git_committer_info(0)` when adding a reflog. The upcoming patches
introduce support for migrating reflogs between the reference backends.
This requires an interface to creating reflogs, including custom
committer information.
Add a new field `committer_info` to the `ref_update` struct, which is
then used by the reference backends. If there is no `committer_info`
provided, the reference backends default to using
`git_committer_info(0)`. The field itself cannot be set to
`git_committer_info(0)` since the values are dynamic and must be
obtained right when the reflog is being committed.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Optimize reading random references out of the reftable backend by
allowing reuse of iterator objects.
* ps/reftable-iterator-reuse:
refs/reftable: reuse iterators when reading refs
reftable/merged: drain priority queue on reseek
reftable/stack: add mechanism to notify callers on reload
refs/reftable: refactor reflog expiry to use reftable backend
refs/reftable: refactor reading symbolic refs to use reftable backend
refs/reftable: read references via `struct reftable_backend`
refs/reftable: figure out hash via `reftable_stack`
reftable/stack: add accessor for the hash ID
refs/reftable: handle reloading stacks in the reftable backend
refs/reftable: encapsulate reftable stack
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Isolates the reftable subsystem from the rest of Git's codebase by
using fewer pieces of Git's infrastructure.
* ps/reftable-detach:
reftable/system: provide thin wrapper for lockfile subsystem
reftable/stack: drop only use of `get_locked_file_path()`
reftable/system: provide thin wrapper for tempfile subsystem
reftable/stack: stop using `fsync_component()` directly
reftable/system: stop depending on "hash.h"
reftable: explicitly handle hash format IDs
reftable/system: move "dir.h" to its only user
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We have a bunch of loops which iterate up to an unsigned boundary using
a signed index, which generates warnigs because we compare a signed and
unsigned value in the loop condition. Address these sites for trivial
cases and enable `-Wsign-compare` warnings for these code units.
This patch only adapts those code units where we can drop the
`DISABLE_SIGN_COMPARE_WARNINGS` macro in the same step.
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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A double-free that may not trigger in practice by luck has been
corrected in the reference resolution code.
* sj/refs-symref-referent-fix:
ref-cache: fix invalid free operation in `free_ref_entry`
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"git fsck" learned to issue warnings on "curiously formatted" ref
contents that have always been taken valid but something Git
wouldn't have written itself (e.g., missing terminating end-of-line
after the full object name).
* sj/ref-contents-check:
ref: add symlink ref content check for files backend
ref: check whether the target of the symref is a ref
ref: add basic symref content check for files backend
ref: add more strict checks for regular refs
ref: port git-fsck(1) regular refs check for files backend
ref: support multiple worktrees check for refs
ref: initialize ref name outside of check functions
ref: check the full refname instead of basename
ref: initialize "fsck_ref_report" with zero
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In cfd971520e (refs: keep track of unresolved reference value in
iterators, 2024-08-09), we added a new field "referent" into the "struct
ref" structure. In order to free the "referent", we unconditionally
freed the "referent" by simply adding a "free" statement.
However, this is a bad usage. Because when ref entry is either directory
or loose ref, we will always execute the following statement:
free(entry->u.value.referent);
This does not make sense. We should never access the "entry->u.value"
field when "entry" is a directory. However, the change obviously doesn't
break the tests. Let's analysis why.
The anonymous union in the "ref_entry" has two members: one is "struct
ref_value", another is "struct ref_dir". On a 64-bit machine, the size
of "struct ref_dir" is 32 bytes, which is smaller than the 48-byte size
of "struct ref_value". And the offset of "referent" field in "struct
ref_value" is 40 bytes. So, whenever we create a new "ref_entry" for a
directory, we will leave the offset from 40 bytes to 48 bytes untouched,
which means the value for this memory is zero (NULL). It's OK to free a
NULL pointer, but this is merely a coincidence of memory layout.
To fix this issue, we now ensure that "free(entry->u.value.referent)" is
only called when "entry->flag" indicates that it represents a loose
reference and not a directory to avoid the invalid memory operation.
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When reading references the reftable backend has to:
1. Create a new ref iterator.
2. Seek the iterator to the record we're searching for.
3. Read the record.
We cannot really avoid the last two steps, but re-creating the iterator
every single time we want to read a reference is kind of expensive and a
waste of resources. We couldn't help it in the past though because it
was not possible to reuse iterators. But starting with 5bf96e0c39
(reftable/generic: move seeking of records into the iterator,
2024-05-13) we have split up the iterator lifecycle such that creating
the iterator and seeking are two different concerns.
Refactor the code such that we cache iterators in the reftable backend.
This cache is invalidated whenever the respective stack is reloaded such
that we know to recreate the iterator in that case. This leads to a
sizeable speedup when creating many refs, which requires a lot of random
reference reads:
Benchmark 1: update-ref: create many refs (refcount = 100000, revision = master)
Time (mean ± σ): 1.793 s ± 0.010 s [User: 0.954 s, System: 0.835 s]
Range (min … max): 1.781 s … 1.811 s 10 runs
Benchmark 2: update-ref: create many refs (refcount = 100000, revision = HEAD)
Time (mean ± σ): 1.680 s ± 0.013 s [User: 0.846 s, System: 0.831 s]
Range (min … max): 1.664 s … 1.702 s 10 runs
Summary
update-ref: create many refs (refcount = 100000, revision = HEAD) ran
1.07 ± 0.01 times faster than update-ref: create many refs (refcount = 100000, revision = master)
While 7% is not a huge win, you have to consider that the benchmark is
_writing_ data, so _reading_ references is only one part of what we do.
Flame graphs show that we spend around 40% of our time reading refs, so
the speedup when reading refs is approximately ~2.5x that. I could not
find better benchmarks where we perform a lot of random ref reads.
You can also see a sizeable impact on memory usage when creating 100k
references. Before this change:
HEAP SUMMARY:
in use at exit: 19,112,538 bytes in 200,170 blocks
total heap usage: 8,400,426 allocs, 8,200,256 frees, 454,367,048 bytes allocated
After this change:
HEAP SUMMARY:
in use at exit: 674,416 bytes in 169 blocks
total heap usage: 7,929,872 allocs, 7,929,703 frees, 281,509,985 bytes allocated
As an additional factor, this refactoring opens up the possibility for
more performance optimizations in how we re-seek iterators. Any change
that allows us to optimize re-seeking by e.g. reusing data structures
would thus also directly speed up random reads.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Refactor the callback function that expires reflog entries in the
reftable backend to use `reftable_backend_read_ref()` instead of
accessing the reftable stack directly. This ensures that the function
will benefit from the new caching layer that we're about to introduce.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Refactor the callback function that reads symbolic references in the
reftable backend to use `reftable_backend_read_ref()` instead of
accessing the reftable stack directly. This ensures that the function
will benefit from the new caching layer that we're about to introduce.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Refactor `read_ref_without_reload()` to accept `struct reftable_backend`
as parameter instead of `struct reftable_stack`. Rename the function to
`reftable_backend_read_ref()` to clarify its scope and move it close to
other functions operating on `struct reftable_backend`.
This change allows us to implement an additional caching layer when
reading refs where we can reuse reftable iterators.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The function `read_ref_without_reload()` accepts a ref store as input
only so that we can figure out the hash function used by it. This is
duplicate information though because the reftable stack knows about its
hash function, too.
Drop the superfluous parameter to simplify the calling convention a bit.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When accessing a stack we almost always have to reload the stack before
reading data from it. This is mostly because Git does not have a
notification mechanism for when underlying data has been changed, and
thus we are forced to opportunistically reload the stack every single
time to account for any changes that may have happened concurrently.
Handle the reload internally in `backend_for()`. For one this forces
callsites to think about whether or not they need to reload the stack.
But second this makes the logic to access stacks more self-contained by
letting the `struct reftable_backend` manage themselves.
Update callsites where we don't reload the stack to document why we
don't. In some cases it's unclear whether it is the right thing to do in
the first place, but fixing that is outside of 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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The reftable ref store needs to keep track of multiple stacks, one for
the main worktree and an arbitrary number of stacks for worktrees. This
is done by storing pointers to `struct reftable_stack`, which we then
access directly.
Wrap the stack in a new `struct reftable_backend`. This will allow us to
attach more data to each respective stack in subsequent commits.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Currently there is only one special error for transaction, for when
there is a naming conflict, all other errors are dumped under a generic
error. Add a new special error case for when the caller requests the
reference to be updated only when it does not yet exist and the
reference actually does exist.
Signed-off-by: Bence Ferdinandy <bence@ferdinandy.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When the symbolic reference we want to read with refs_read_symbolic_ref
is actually not a symbolic reference, the files and the reftable
backends return different values (1 and -1 respectively). Standardize
the returned values so that 0 is success, -1 is a generic error and -2
is that the reference was actually non-symbolic.
Signed-off-by: Bence Ferdinandy <bence@ferdinandy.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Besides the textual symref, we also allow symbolic links as the symref.
So, we should also provide the consistency check as what we have done
for textual symref. And also we consider deprecating writing the
symbolic links. We first need to access whether symbolic links still
be used. So, add a new fsck message "symlinkRef(INFO)" to tell the
user be aware of this information.
We have already introduced "files_fsck_symref_target". We should reuse
this function to handle the symrefs which use legacy symbolic links. We
should not check the trailing garbage for symbolic refs. Add a new
parameter "symbolic_link" to disable some checks which should only be
executed for textual symrefs.
And we need to also generate the "referent" parameter for reusing
"files_fsck_symref_target" by the following steps:
1. Use "strbuf_add_real_path" to resolve the symlink and get the
absolute path "ref_content" which the symlink ref points to.
2. Generate the absolute path "abs_gitdir" of "gitdir" and combine
"ref_content" and "abs_gitdir" to extract the relative path
"relative_referent_path".
3. If "ref_content" is outside of "gitdir", we just set "referent" with
"ref_content". Instead, we set "referent" with
"relative_referent_path".
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Ideally, we want to the users use "git symbolic-ref" to create symrefs
instead of writing raw contents into the filesystem. However, "git
symbolic-ref" is strict with the refname but not strict with the
referent. For example, we can make the "referent" located at the
"$(gitdir)/logs/aaa" and manually write the content into this where we
can still successfully parse this symref by using "git rev-parse".
$ git init repo && cd repo && git commit --allow-empty -mx
$ git symbolic-ref refs/heads/test logs/aaa
$ echo $(git rev-parse HEAD) > .git/logs/aaa
$ git rev-parse test
We may need to add some restrictions for "referent" parameter when using
"git symbolic-ref" to create symrefs because ideally all the
nonpseudo-refs should be located under the "refs" directory and we may
tighten this in the future.
In order to tell the user we may tighten the above situation, create
a new fsck message "symrefTargetIsNotARef" to notify the user that this
may become an error in the future.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We have code that checks regular ref contents, but we do not yet check
the contents of symbolic refs. By using "parse_loose_ref_content" for
symbolic refs, we will get the information of the "referent".
We do not need to check the "referent" by opening the file. This is
because if "referent" exists in the file system, we will eventually
check its correctness by inspecting every file in the "refs" directory.
If the "referent" does not exist in the filesystem, this is OK as it is
seen as the dangling symref.
So we just need to check the "referent" string content. A regular ref
could be accepted as a textual symref if it begins with "ref:", followed
by zero or more whitespaces, followed by the full refname, followed only
by whitespace characters. However, we always write a single SP after
"ref:" and a single LF after the refname. It may seem that we should
report a fsck error message when the "referent" does not apply above
rules and we should not be so aggressive because third-party
reimplementations of Git may have taken advantage of the looser syntax.
Put it more specific, we accept the following contents:
1. "ref: refs/heads/master "
2. "ref: refs/heads/master \n \n"
3. "ref: refs/heads/master\n\n"
When introducing the regular ref content checks, we created two fsck
infos "refMissingNewline" and "trailingRefContent" which exactly
represents above situations. So we will reuse these two fsck messages to
write checks to info the user about these situations.
But we do not allow any other trailing garbage. The followings are bad
symref contents which will be reported as fsck error by "git-fsck(1)".
1. "ref: refs/heads/master garbage\n"
2. "ref: refs/heads/master \n\n\n garbage "
And we introduce a new "badReferentName(ERROR)" fsck message to report
above errors by using "is_root_ref" and "check_refname_format" to check
the "referent". Since both "is_root_ref" and "check_refname_format"
don't work with whitespaces, we use the trimmed version of "referent"
with these functions.
In order to add checks, we will do the following things:
1. Record the untrimmed length "orig_len" and untrimmed last byte
"orig_last_byte".
2. Use "strbuf_rtrim" to trim the whitespaces or newlines to make sure
"is_root_ref" and "check_refname_format" won't be failed by them.
3. Use "orig_len" and "orig_last_byte" to check whether the "referent"
misses '\n' at the end or it has trailing whitespaces or newlines.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We have already used "parse_loose_ref_contents" function to check
whether the ref content is valid in files backend. However, by
using "parse_loose_ref_contents", we allow the ref's content to end with
garbage or without a newline.
Even though we never create such loose refs ourselves, we have accepted
such loose refs. So, it is entirely possible that some third-party tools
may rely on such loose refs being valid. We should not report an error
fsck message at current. We should notify the users about such
"curiously formatted" loose refs so that adequate care is taken before
we decide to tighten the rules in the future.
And it's not suitable either to report a warn fsck message to the user.
We don't yet want the "--strict" flag that controls this bit to end up
generating errors for such weirdly-formatted reference contents, as we
first want to assess whether this retroactive tightening will cause
issues for any tools out there. It may cause compatibility issues which
may break the repository. So, we add the following two fsck infos to
represent the situation where the ref content ends without newline or
has trailing garbages:
1. refMissingNewline(INFO): A loose ref that does not end with
newline(LF).
2. trailingRefContent(INFO): A loose ref has trailing content.
It might appear that we can't provide the user with any warnings by
using FSCK_INFO. However, in "fsck.c::fsck_vreport", we will convert
FSCK_INFO to FSCK_WARN and we can still warn the user about these
situations when using "git refs verify" without introducing
compatibility issues.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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"git-fsck(1)" implicitly checks the ref content by passing the
callback "fsck_handle_ref" to the "refs.c::refs_for_each_rawref".
Then, it will check whether the ref content (eventually "oid")
is valid. If not, it will report the following error to the user.
error: refs/heads/main: invalid sha1 pointer 0000...
And it will also report above errors when there are dangling symrefs
in the repository wrongly. This does not align with the behavior of
the "git symbolic-ref" command which allows users to create dangling
symrefs.
As we have already introduced the "git refs verify" command, we'd better
check the ref content explicitly in the "git refs verify" command thus
later we could remove these checks in "git-fsck(1)" and launch a
subprocess to call "git refs verify" in "git-fsck(1)" to make the
"git-fsck(1)" more clean.
Following what "git-fsck(1)" does, add a similar check to "git refs
verify". Then add a new fsck error message "badRefContent(ERROR)" to
represent that a ref has an invalid content.
Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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