The ref storage format is tracked as a simple unsigned integer, which
makes it harder than necessary to discover what that integer actually is
or where its values are defined.
Convert the ref storage format to instead be an enum.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
* ps/pseudo-ref-terminology:
refs: refuse to write pseudorefs
ref-filter: properly distinuish pseudo and root refs
refs: pseudorefs are no refs
refs: classify HEAD as a root ref
refs: do not check ref existence in `is_root_ref()`
refs: rename `is_special_ref()` to `is_pseudo_ref()`
refs: rename `is_pseudoref()` to `is_root_ref()`
Documentation/glossary: define root refs as refs
Documentation/glossary: clarify limitations of pseudorefs
Documentation/glossary: redefine pseudorefs as special refs
Updates to symbolic refs can now be made as a part of ref
transaction.
* kn/ref-transaction-symref:
refs: remove `create_symref` and associated dead code
refs: rename `refs_create_symref()` to `refs_update_symref()`
refs: use transaction in `refs_create_symref()`
refs: add support for transactional symref updates
refs: move `original_update_refname` to 'refs.c'
refs: support symrefs in 'reference-transaction' hook
files-backend: extract out `create_symref_lock()`
refs: accept symref values in `ref_transaction_update()`
Remove `dwim_log()` in favor of `repo_dwim_log()` so that we can get rid
of one more dependency on `the_repository`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `git_default_branch_name()` function is a thin wrapper around
`repo_default_branch_name()` with two differences:
- We implicitly rely on `the_repository`.
- We cache the default branch name.
None of the callsites of `git_default_branch_name()` are hot code paths
though, so the caching of the branch name is not really required.
Refactor the callsites to use `repo_default_branch_name()` instead and
drop `git_default_branch_name()`, thus getting rid of one more case
where we rely on `the_repository`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both `peel_object()` and `peel_iterated_oid()` implicitly rely on
`the_repository` to look up objects. Despite the fact that we want to
get rid of `the_repository`, it also leads to some restrictions in our
ref iterators when trying to retrieve the peeled value for a repository
other than `the_repository`.
Refactor these functions such that both take a repository as argument
and remove the now-unnecessary restrictions.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Peeling an object has nothing to do with refs, but we still have the
code in "refs.c". Move it over into "object.c", which is a more natural
place to put it.
Ideally, we'd also move `peel_iterated_oid()` over into "object.c". But
this function is tied to the refs interfaces because it uses a global
ref iterator variable to optimize peeling when the iterator already has
the peeled object ID readily available.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Both `warn_dangling_symref()` and `warn_dangling_symrefs()` derive the
ref store via `the_repository`. Adapt them to instead take in the ref
store as a parameter. While at it, rename the functions to have a `ref_`
prefix to align them with other functions that take a ref store.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The function `for_each_replace_ref()` is a bit of an oddball across the
refs interfaces as it accepts a pointer to the repository instead of a
pointer to the ref store. The only reason for us to accept a repository
is so that we can eventually pass it back to the callback function that
the caller has provided. This is somewhat arbitrary though, as callers
that need the repository can instead make it accessible via the callback
payload.
Refactor the function to instead accept the ref store and adjust callers
accordingly. This allows us to get rid of some of the boilerplate that
we had to carry to pass along the repository and brings us in line with
the other functions that iterate through refs.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar as with the preceding commit, the worktree ref stores are always
looked up via `the_repository`. Also, again, those ref stores are stored
in a global map.
Refactor the code so that worktrees have a pointer to their repository.
Like this, we can move the global map into `struct repository` and stop
using `the_repository`. With this change, we can now in theory look up
worktree ref stores for repositories other than `the_repository`. In
practice, the worktree code will need further changes to look up
arbitrary worktrees.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In `resolve_gitlink_ref()` we implicitly rely on `the_repository` to
look up the submodule ref store. Now that we can look up submodule ref
stores for arbitrary repositories we can improve this function to
instead accept a repository as parameter for which we want to resolve
the gitlink.
Do so and adjust callers accordingly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Looking up submodule ref stores has two deficiencies:
- The initialized subrepo will be attributed to `the_repository`.
- The submodule ref store will be tracked in a global map.
This makes it impossible to have submodule ref stores for a repository
other than `the_repository`.
Modify the function to accept the parent repository as parameter and
move the global map into `struct repository`. Like this it becomes
possible to look up submodule ref stores for arbitrary repositories.
Note that this also adds a new reference to `the_repository` in
`resolve_gitlink_ref()`, which is part of the refs interfaces. This will
get adjusted in the next patch.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The refs code has two global maps that track the submodule and worktree
ref stores. Even though both of these maps track values by strings, we
still use a `struct hashmap` instead of a `struct strmap`. This has the
benefit of saving us an allocation because we can combine key and value
in a single struct. But it does introduce significant complexity that is
completely unneeded.
Refactor the code to use `struct strmap`s instead to reduce complexity.
It's unlikely that this will have any real-world impact on performance
given that most repositories likely won't have all that many ref stores.
Furthermore, this refactoring allows us to de-globalize those maps and
move them into `struct repository` in a subsequent commit more easily.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Ref storages are typically only initialized once for `the_repository`
and then never released. Until now we got away with that without causing
memory leaks because `the_repository` stays reachable, and because the
ref backend is reachable via `the_repository` its memory basically never
leaks.
This is about to change though because of the upcoming migration logic,
which will create a secondary ref storage. In that case, we will either
have to release the old or new ref storage to avoid leaks.
Implement a new `release` callback and expose it via a new
`ref_storage_release()` function.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Reference backends have two callbacks `init` and `init_db`. The
similarity of these two callbacks has repeatedly confused me whenever I
was looking at them, where I always had to look up which of them does
what.
Rename the `init_db` callback to `create_on_disk`, which should
hopefully be clearer.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Pseudorefs are not stored in the ref database as by definition, they
carry additional metadata that essentially makes them not a ref. As
such, writing pseudorefs via the ref backend does not make any sense
whatsoever as the ref backend wouldn't know how exactly to store the
data.
Restrict writing pseudorefs via the ref backend.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ref-filter interfaces currently define root refs as either a
detached HEAD or a pseudo ref. Pseudo refs aren't root refs though, so
let's properly distinguish those ref types.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `is_root_ref()` function will happily clarify a pseudoref as a root
ref, even though pseudorefs are no refs. Next to being wrong, it also
leads to inconsistent behaviour across ref backends: while the "files"
backend accidentally knows to parse those pseudorefs and thus yields
them to the caller, the "reftable" backend won't ever see the pseudoref
at all because they are never stored in the "reftable" backend.
Fix this issue by filtering out pseudorefs in `is_root_ref()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Root refs are those refs that live in the root of the ref hierarchy.
Our old and venerable "HEAD" reference falls into this category, but we
don't yet classify it as such in `is_root_ref()`.
Adapt the function to also treat "HEAD" as a root ref. This change is
safe to do for all current callers:
- `ref_kind_from_refname()` already handles "HEAD" explicitly before
calling `is_root_ref()`.
- The "files" and "reftable" backends explicitly call both
`is_root_ref()` and `is_headref()` together.
This also aligns behaviour or `is_root_ref()` and `is_headref()` such
that we stop checking for ref existence. This changes semantics for our
backends:
- In the reftable backend we already know that the ref must exist
because `is_headref()` is called as part of the ref iterator. The
existence check is thus redundant, and the change is safe to do.
- In the files backend we use it when populating root refs, where we
would skip adding the "HEAD" file if it was not possible to resolve
it. The new behaviour is to instead mark "HEAD" as broken, which
will cause us to emit warnings in various places.
As there are no callers of `is_headref()` left afer the refactoring, we
can absorb it completely into `is_root_ref()`.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Before this patch series, root refs except for "HEAD" and our special
refs were classified as pseudorefs. Furthermore, our terminology
clarified that pseudorefs must not be symbolic refs. This restriction
is enforced in `is_root_ref()`, which explicitly checks that a supposed
root ref resolves to an object ID without recursing.
This has been extremely confusing right from the start because (in old
terminology) a ref name may sometimes be a pseudoref and sometimes not
depending on whether it is a symbolic or regular ref. This behaviour
does not seem reasonable at all and I very much doubt that it results in
anything sane.
Last but not least, the current behaviour can actually lead to a
segfault when calling `is_root_ref()` with a reference that either does
not exist or that is a symbolic ref because we never initialized `oid`,
but then read it via `is_null_oid()`.
We have now changed terminology to clarify that pseudorefs are really
only "MERGE_HEAD" and "FETCH_HEAD", whereas all the other refs that live
in the root of the ref hierarchy are just plain refs. Thus, we do not
need to check whether the ref is symbolic or not. In fact, we can now
avoid looking up the ref completely as the name is sufficient for us to
figure out whether something would be a root ref or not.
This change of course changes semantics for our callers. As there are
only three of them we can assess each of them individually:
- "ref-filter.c:ref_kind_from_refname()" uses it to classify refs.
It's clear that the intent is to classify based on the ref name,
only.
- "refs/reftable_backend.c:reftable_ref_iterator_advance()" uses it to
filter root refs. Again, using existence checks is pointless here as
the iterator has just surfaced the ref, so we know it does exist.
- "refs/files_backend.c:add_pseudoref_and_head_entries()" uses it to
determine whether it should add a ref to the root directory of its
iterator. This had the effect that we skipped over any files that
are either a symbolic ref, or which are not a ref at all.
The new behaviour is to include symbolic refs know, which aligns us
with the adapted terminology. Furthermore, files which look like
root refs but aren't are now mark those as "broken". As broken refs
are not surfaced by our tooling, this should not lead to a change in
user-visible behaviour, but may cause us to emit warnings. This
feels like the right thing to do as we would otherwise just silently
ignore corrupted root refs completely.
So in all cases the existence check was either superfluous, not in line
with the adapted terminology or masked potential issues. This commit
thus changes the behaviour as proposed and drops the existence check
altogether.
Add a test that verifies that this does not change user-visible
behaviour. Namely, we still don't want to show broken refs to the user
by default in git-for-each-ref(1). What this does allow though is for
internal callers to surface dangling root refs when they pass in the
`DO_FOR_EACH_INCLUDE_BROKEN` flag.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Rename `is_special_ref()` to `is_pseudo_ref()` to adapt to the newly
defined terminology in our gitglossary(7). Note that in the preceding
commit we have just renamed `is_pseudoref()` to `is_root_ref()`, where
there may be confusion for in-flight patch series that add new calls to
`is_pseudoref()`. In order to intentionally break such patch series we
have thus picked `is_pseudo_ref()` instead of `is_pseudoref()` as the
new name.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Rename `is_pseudoref()` to `is_root_ref()` to adapt to the newly defined
terminology in our gitglossary(7).
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The preceding commit has rewritten all callers of ref-related functions
to use the equivalents that accept a `struct ref_store`. Consequently,
the respective variants without the ref store are now unused. Remove
them.
There are likely patch series in-flight that use the now-removed
functions. To help the authors, the old implementations have been added
to "refs.c" in an ifdef'd section as a reference for how to migrate each
of the respective callers.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Apply the rules that rewrite callers of "refs" interfaces to explicitly
pass `struct ref_store`. The resulting patch has been applied with the
`--whitespace=fix` option.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `for_each_fullref_in()` function is supposedly the ref-store-less
equivalent of `refs_for_each_fullref_in()`, but the latter has gained a
new parameter `exclude_patterns` over time. Bring these two functions
back in sync again by adding the parameter to the former function, as
well.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
While most of the functions in "refs.h" have a variant that accepts a
`struct ref_store`, some don't. Callers of these functions are thus
forced to implicitly rely on `the_repository` to figure out the ref
store that is to be used.
Introduce those missing functions to address this shortcoming.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `refs_create_symref()` function is used to update/create a symref.
But it doesn't check the old target of the symref, if existing. It force
updates the symref. In this regard, the name `refs_create_symref()` is a
bit misleading. So let's rename it to `refs_update_symref()`. This is
akin to how 'git-update-ref(1)' also allows us to create apart from
update.
While we're here, rename the arguments in the function to clarify what
they actually signify and reduce confusion.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The `refs_create_symref()` function updates a symref to a given new
target. To do this, it uses a ref-backend specific function
`create_symref()`.
In the previous commits, we introduced symref support in transactions.
This means we can now use transactions to perform symref updates and
don't have to resort to `create_symref()`. Doing this allows us to
remove and cleanup `create_symref()`, which we will do in the following
commit.
Modify the expected error message for a test in
't/t0610-reftable-basics.sh', since the error is now thrown from
'refs.c'. This is because in transactional updates, F/D conflicts are
caught before we're in the reference backend.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The reference backends currently support transactional reference
updates. While this is exposed to users via 'git-update-ref' and its
'--stdin' mode, it is also used internally within various commands.
However, we do not support transactional updates of symrefs. This commit
adds support for symrefs in both the 'files' and the 'reftable' backend.
Here, we add and use `ref_update_has_null_new_value()`, a helper
function which is used to check if there is a new_value in a reference
update. The new value could either be a symref target `new_target` or a
OID `new_oid`.
We also add another common function `ref_update_check_old_target` which
will be used to check if the update's old_target corresponds to a
reference's current target.
Now transactional updates (verify, create, delete, update) can be used
for:
- regular refs
- symbolic refs
- conversion of regular to symbolic refs and vice versa
This also allows us to expose this to users via new commands in
'git-update-ref' in the future.
Note that a dangling symref update does not record a new reflog entry,
which is unchanged before and after this commit.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The files backend and the reftable backend implement
`original_update_refname` to obtain the original refname of the update.
Move it out to 'refs.c' and only expose it internally to the refs
library. This will be used in an upcoming commit to also introduce
another common functionality for the two backends.
We also rename the function to `ref_update_original_update_refname` to
keep it consistent with the upcoming other 'ref_update_*' functions
that'll be introduced.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The 'reference-transaction' hook runs whenever a reference update is
made to the system. In a previous commit, we added the `old_target` and
`new_target` fields to the `reference_transaction_update()`. In
following commits we'll also add the code to handle symref's in the
reference backends.
Support symrefs also in the 'reference-transaction' hook, by modifying
the current format:
<old-oid> SP <new-oid> SP <ref-name> LF
to be be:
<old-value> SP <new-value> SP <ref-name> LF
where for regular refs the output would not change and remain the same.
But when either 'old-value' or 'new-value' is a symref, we print the ref
as 'ref:<ref-target>'.
This does break backward compatibility, but the 'reference-transaction'
hook's documentation always stated that support for symbolic references
may be added in the future.
We do not add any tests in this commit since there is no git command
which activates this flow, in an upcoming commit, we'll start using
transaction based symref updates as the default, we'll add tests there
for the hook too.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The function `ref_transaction_update()` obtains ref information and
flags to create a `ref_update` and add them to the transaction at hand.
To extend symref support in transactions, we need to also accept the
old and new ref targets and process it. This commit adds the required
parameters to the function and modifies all call sites.
The two parameters added are `new_target` and `old_target`. The
`new_target` is used to denote what the reference should point to when
the transaction is applied. Some functions allow this parameter to be
NULL, meaning that the reference is not changed.
The `old_target` denotes the value the reference must have before the
update. Some functions allow this parameter to be NULL, meaning that the
old value of the reference is not checked.
We also update the internal function `ref_transaction_add_update()`
similarly to take the two new parameters.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
"git for-each-ref" learned "--include-root-refs" option to show
even the stuff outside the 'refs/' hierarchy.
* kn/for-all-refs:
for-each-ref: add new option to include root refs
ref-filter: rename 'FILTER_REFS_ALL' to 'FILTER_REFS_REGULAR'
refs: introduce `refs_for_each_include_root_refs()`
refs: extract out `loose_fill_ref_dir_regular_file()`
refs: introduce `is_pseudoref()` and `is_headref()`
The logic to access reflog entries by date and number had ugly
corner cases at the boundaries, which have been cleaned up.
* jk/reflog-special-cases-fix:
read_ref_at(): special-case ref@{0} for an empty reflog
get_oid_basic(): special-case ref@{n} for oldest reflog entry
Revert "refs: allow @{n} to work with n-sized reflog"
The previous commit special-cased get_oid_basic()'s handling of ref@{n}
for a reflog with n entries. But its special case doesn't work for
ref@{0} in an empty reflog, because read_ref_at() dies when it notices
the empty reflog!
We can make this work by special-casing this in read_ref_at(). It's
somewhat gross, for two reasons:
1. We have no reflog entry to describe in the "msg" out-parameter. So
we have to leave it uninitialized or make something up.
2. Likewise, we have no oid to put in the "oid" out-parameter. Leaving
it untouched is actually the best thing here, as all of the callers
will have initialized it with the current ref value via
repo_dwim_log(). This is rather subtle, but it is how things worked
in 6436a20284 (refs: allow @{n} to work with n-sized reflog,
2021-01-07) before we reverted it.
The key difference from 6436a20284 here is that we'll return "1" to
indicate that we _didn't_ find the requested reflog entry. Coupled with
the special-casing in get_oid_basic() in the previous commit, that's
enough to make looking up ref@{0} work, and we can flip 6436a20284's
test back to expect_success.
It also means that the call in show-branch which segfaulted with
6436a20284 (and which is now tested in t3202) remains OK. The caller
notices that we could not find any reflog entry, and so it breaks out of
its loop, showing nothing. This is different from the current behavior
of producing an error, but it's just as reasonable (and is exactly what
we'd do if you asked it to walk starting at ref@{1} but there was only 1
entry).
Thus nobody should actually look at the reflog entry info we return. But
we'll still put in some fake values just to be on the safe side, since
this is such a subtle and confusing interface. Likewise, we'll document
what's going on in a comment above the function declaration. If this
were a function with a lot of callers, the footgun would probably not be
worth it. But it has only ever had two callers in its 18-year existence,
and it seems unlikely to grow more. So let's hold our noses and let
users enjoy the convenience of a simulated ref@{0}.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The goal of 6436a20284 (refs: allow @{n} to work with n-sized reflog,
2021-01-07) was that if we have "n" entries in a reflog, we should still
be able to resolve ref@{n} by looking at the "old" value of the oldest
entry.
Commit 6436a20284 tried to put the logic into read_ref_at() by shifting
its idea of "n" by one. But we reverted that in the previous commit,
since it led to bugs in other callers which cared about the details of
the reflog entry we found. Instead, let's put the special case into the
caller that resolves @{n}, as it cares only about the oid.
read_ref_at() is even kind enough to return the "old" value from the
final reflog; it just returns "1" to signal to us that we ran off the
end of the reflog. But we can notice in the caller that we read just
enough records for that "old" value to be the one we're looking for, and
use it.
Note that read_ref_at() could notice this case, too, and just return 0.
But we don't want to do that, because the caller must be made aware that
we only found the oid, not an actual reflog entry (and the call sites in
show-branch do care about this).
There is one complication, though. When read_ref_at() hits a truncated
reflog, it will return the "old" value of the oldest entry only if it is
not the null oid. Otherwise, it actually returns the "new" value from
that entry! This bit of fudging is due to d1a4489a56 (avoid null SHA1 in
oldest reflog, 2008-07-08), where asking for "ref@{20.years.ago}" for a
ref created recently will produce the initial value as a convenience
(even though technically it did not exist 20 years ago).
But this convenience is only useful for time-based cutoffs. For
count-based cutoffs, get_oid_basic() has always simply complained about
going too far back:
$ git rev-parse HEAD@{20}
fatal: log for 'HEAD' only has 16 entries
and we should continue to do so, rather than returning a nonsense value
(there's even a test in t1508 already which covers this). So let's have
the d1a4489a56 code kick in only when doing timestamp-based cutoffs.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This reverts commit 6436a20284.
The idea of that commit is that if read_ref_at() is counting back to the
Nth reflog but the reflog is short by one entry (e.g., because it was
pruned), we can find the oid of the missing entry by looking at the
"before" oid value of the entry that comes after it (whereas before, we
looked at the "after" value of each entry and complained that we
couldn't find the one from before the truncation).
This works fine for resolving the oid of ref@{n}, as it is used by
get_oid_basic(), which does not look at any other aspect of the reflog
we found (e.g., its timestamp or message). But there's another caller of
read_ref_at(): in show-branch we use it to walk over the reflog, and we
do care about the reflog entry. And so that commit broke "show-branch
--reflog"; it shows the reflog message for ref@{0} as ref@{1}, ref@{1}
as ref@{2}, and so on.
For example, in the new test in t3202 we produce:
! [branch@{0}] (0 seconds ago) commit: three
! [branch@{1}] (0 seconds ago) commit: three
! [branch@{2}] (60 seconds ago) commit: two
! [branch@{3}] (2 minutes ago) reset: moving to HEAD^
instead of the correct:
! [branch@{0}] (0 seconds ago) commit: three
! [branch@{1}] (60 seconds ago) commit: two
! [branch@{2}] (2 minutes ago) reset: moving to HEAD^
! [branch@{3}] (2 minutes ago) commit: one
But there's another bug, too: because it is looking at the "old" value
of the reflog after the one we're interested in, it has to special-case
ref@{0} (since there isn't anything after it). That's why it doesn't
show the offset bug in the output above. But this special-case code
fails to handle the situation where the reflog is empty or missing; it
returns success even though the reflog message out-parameter has been
left uninitialized. You can't trigger this through get_oid_basic(), but
"show-branch --reflog" will pretty reliably segfault as it tries to
access the garbage pointer.
Fixing the segfault would be pretty easy. But the off-by-one problem is
inherent in this approach. So let's start by reverting the commit to
give us a clean slate to work with.
This isn't a pure revert; all of the code changes are reverted, but for
the tests:
1. We'll flip the cases in t1508 to expect_failure; making these work
was the goal of 6436a2028, and we'll want to use them for our
replacement approach.
2. There's a test in t3202 for "show-branch --reflog", but it expects
the broken output! It was added by f2463490c4 (show-branch: show
reflog message, 2021-12-02) which was fixing another bug, and I
think the author simply didn't notice that the second line showed
the wrong reflog.
Rather than fixing that test, let's replace it with one that is
more thorough (while still covering the reflog message fix from
that commit). We'll use a longer reflog, which lets us see more
entries (thus making the "off by one" pattern much more clear). And
we'll use a more recent timestamp for "now" so that our relative
dates have more resolution. That lets us see that the reflog dates
are correct (whereas when you are 4 years away, two entries that
are 60 seconds apart will have the same "4 years ago" relative
date). Because we're adjusting the repository state, I've moved
this new test to the end of the script, leaving the other tests
undisturbed.
We'll also add a new test which covers the missing reflog case;
previously it segfaulted, but now it reports the empty reflog).
Reported-by: Yasushi SHOJI <yasushi.shoji@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a new ref iteration flag `DO_FOR_EACH_INCLUDE_ROOT_REFS`,
which will be used to iterate over regular refs plus pseudorefs and
HEAD.
Refs which fall outside the `refs/` and aren't either pseudorefs or HEAD
are more of a grey area. This is because we don't block the users from
creating such refs but they are not officially supported.
Introduce `refs_for_each_include_root_refs()` which calls
`do_for_each_ref()` with this newly introduced flag.
In `refs/files-backend.c`, introduce a new function
`add_pseudoref_and_head_entries()` to add pseudorefs and HEAD to the
`ref_dir`. We then finally call `add_pseudoref_and_head_entries()`
whenever the `DO_FOR_EACH_INCLUDE_ROOT_REFS` flag is set. Any new ref
backend will also have to implement similar changes on its end.
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce two new functions `is_pseudoref()` and `is_headref()`. This
provides the necessary functionality for us to add pseudorefs and HEAD
to the loose ref cache in the files backend, allowing us to build
tooling to print these refs.
The `is_pseudoref()` function internally calls `is_pseudoref_syntax()`
but adds onto it by also checking to ensure that the pseudoref either
ends with a "_HEAD" suffix or matches a list of exceptions. After which
we also parse the contents of the pseudoref to ensure that it conforms
to the ref format.
We cannot directly add the new syntax checks to `is_pseudoref_syntax()`
because the function is also used by `is_current_worktree_ref()` and
making it stricter to match only known pseudorefs might have unintended
consequences due to files like 'BISECT_START' which isn't a pseudoref
but sometimes contains object ID.
Keeping this in mind, we leave `is_pseudoref_syntax()` as is and create
`is_pseudoref()` which is stricter. Ideally we'd want to move the new
syntax checks to `is_pseudoref_syntax()` but a prerequisite for this
would be to actually remove the exception list by converting those
pseudorefs to also contain a '_HEAD' suffix and perhaps move bisect
related files like 'BISECT_START' to a new directory similar to the
'rebase-merge' directory.
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The ref and reflog iterators share much of the same underlying code to
iterate over the corresponding entries. This results in some weird code
because the reflog iterator also exposes an object ID as well as a flag
to the callback function. Neither of these fields do refer to the reflog
though -- they refer to the corresponding ref with the same name. This
is quite misleading. In practice at least the object ID cannot really be
implemented in any other way as a reflog does not have a specific object
ID in the first place. This is further stressed by the fact that none of
the callbacks except for our test helper make use of these fields.
Split up the infrastucture so that ref and reflog iterators use separate
callback signatures. This allows us to drop the nonsensical fields from
the reflog iterator.
Note that internally, the backends still use the same shared infra to
iterate over both types. As the backends should never end up being
called directly anyway, this is not much of a problem and thus kept
as-is for simplicity's sake.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the preceding commit we have converted the reflog iterator of the
"files" backend to be ordered, which was the only remaining ref iterator
that wasn't ordered. Refactor the ref iterator infrastructure so that we
always assume iterators to be ordered, thus simplifying the code.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Due to scalability issues, Shawn Pearce has originally proposed a new
"reftable" format more than six years ago [1]. Initially, this new
format was implemented in JGit with promising results. Around two years
ago, we have then added the "reftable" library to the Git codebase via
a4bbd13be3 (Merge branch 'hn/reftable', 2021-12-15). With this we have
landed all the low-level code to read and write reftables. Notably
missing though was the integration of this low-level code into the Git
code base in the form of a new ref backend that ties all of this
together.
This gap is now finally closed by introducing a new "reftable" backend
into the Git codebase. This new backend promises to bring some notable
improvements to Git repositories:
- It becomes possible to do truly atomic writes where either all refs
are committed to disk or none are. This was not possible with the
"files" backend because ref updates were split across multiple loose
files.
- The disk space required to store many refs is reduced, both compared
to loose refs and packed-refs. This is enabled both by the reftable
format being a binary format, which is more compact, and by prefix
compression.
- We can ignore filesystem-specific behaviour as ref names are not
encoded via paths anymore. This means there is no need to handle
case sensitivity on Windows systems or Unicode precomposition on
macOS.
- There is no need to rewrite the complete refdb anymore every time a
ref is being deleted like it was the case for packed-refs. This
means that ref deletions are now constant time instead of scaling
linearly with the number of refs.
- We can ignore file/directory conflicts so that it becomes possible
to store both "refs/heads/foo" and "refs/heads/foo/bar".
- Due to this property we can retain reflogs for deleted refs. We have
previously been deleting reflogs together with their refs to avoid
file/directory conflicts, which is not necessary anymore.
- We can properly enumerate all refs. With the "files" backend it is
not easily possible to distinguish between refs and non-refs because
they may live side by side in the gitdir.
Not all of these improvements are realized with the current "reftable"
backend implementation. At this point, the new backend is supposed to be
a drop-in replacement for the "files" backend that is used by basically
all Git repositories nowadays. It strives for 1:1 compatibility, which
means that a user can expect the same behaviour regardless of whether
they use the "reftable" backend or the "files" backend for most of the
part.
Most notably, this means we artificially limit the capabilities of the
"reftable" backend to match the limits of the "files" backend. It is not
possible to create refs that would end up with file/directory conflicts,
we do not retain reflogs, we perform stricter-than-necessary checks.
This is done intentionally due to two main reasons:
- It makes it significantly easier to land the "reftable" backend as
tests behave the same. It would be tough to argue for each and every
single test that doesn't pass with the "reftable" backend.
- It ensures compatibility between repositories that use the "files"
backend and repositories that use the "reftable" backend. Like this,
hosters can migrate their repositories to use the "reftable" backend
without causing issues for clients that use the "files" backend in
their clones.
It is expected that these artificial limitations may eventually go away
in the long term.
Performance-wise things very much depend on the actual workload. The
following benchmarks compare the "files" and "reftable" backends in the
current version:
- Creating N refs in separate transactions shows that the "files"
backend is ~50% faster. This is not surprising given that creating a
ref only requires us to create a single loose ref. The "reftable"
backend will also perform auto compaction on updates. In real-world
workloads we would likely also want to perform pack loose refs,
which would likely change the picture.
Benchmark 1: update-ref: create refs sequentially (refformat = files, refcount = 1)
Time (mean ± σ): 2.1 ms ± 0.3 ms [User: 0.6 ms, System: 1.7 ms]
Range (min … max): 1.8 ms … 4.3 ms 133 runs
Benchmark 2: update-ref: create refs sequentially (refformat = reftable, refcount = 1)
Time (mean ± σ): 2.7 ms ± 0.1 ms [User: 0.6 ms, System: 2.2 ms]
Range (min … max): 2.4 ms … 2.9 ms 132 runs
Benchmark 3: update-ref: create refs sequentially (refformat = files, refcount = 1000)
Time (mean ± σ): 1.975 s ± 0.006 s [User: 0.437 s, System: 1.535 s]
Range (min … max): 1.969 s … 1.980 s 3 runs
Benchmark 4: update-ref: create refs sequentially (refformat = reftable, refcount = 1000)
Time (mean ± σ): 2.611 s ± 0.013 s [User: 0.782 s, System: 1.825 s]
Range (min … max): 2.597 s … 2.622 s 3 runs
Benchmark 5: update-ref: create refs sequentially (refformat = files, refcount = 100000)
Time (mean ± σ): 198.442 s ± 0.241 s [User: 43.051 s, System: 155.250 s]
Range (min … max): 198.189 s … 198.670 s 3 runs
Benchmark 6: update-ref: create refs sequentially (refformat = reftable, refcount = 100000)
Time (mean ± σ): 294.509 s ± 4.269 s [User: 104.046 s, System: 190.326 s]
Range (min … max): 290.223 s … 298.761 s 3 runs
- Creating N refs in a single transaction shows that the "files"
backend is significantly slower once we start to write many refs.
The "reftable" backend only needs to update two files, whereas the
"files" backend needs to write one file per ref.
Benchmark 1: update-ref: create many refs (refformat = files, refcount = 1)
Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.4 ms, System: 1.4 ms]
Range (min … max): 1.8 ms … 2.6 ms 151 runs
Benchmark 2: update-ref: create many refs (refformat = reftable, refcount = 1)
Time (mean ± σ): 2.5 ms ± 0.1 ms [User: 0.7 ms, System: 1.7 ms]
Range (min … max): 2.4 ms … 3.4 ms 148 runs
Benchmark 3: update-ref: create many refs (refformat = files, refcount = 1000)
Time (mean ± σ): 152.5 ms ± 5.2 ms [User: 19.1 ms, System: 133.1 ms]
Range (min … max): 148.5 ms … 167.8 ms 15 runs
Benchmark 4: update-ref: create many refs (refformat = reftable, refcount = 1000)
Time (mean ± σ): 58.0 ms ± 2.5 ms [User: 28.4 ms, System: 29.4 ms]
Range (min … max): 56.3 ms … 72.9 ms 40 runs
Benchmark 5: update-ref: create many refs (refformat = files, refcount = 1000000)
Time (mean ± σ): 152.752 s ± 0.710 s [User: 20.315 s, System: 131.310 s]
Range (min … max): 152.165 s … 153.542 s 3 runs
Benchmark 6: update-ref: create many refs (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 51.912 s ± 0.127 s [User: 26.483 s, System: 25.424 s]
Range (min … max): 51.769 s … 52.012 s 3 runs
- Deleting a ref in a fully-packed repository shows that the "files"
backend scales with the number of refs. The "reftable" backend has
constant-time deletions.
Benchmark 1: update-ref: delete ref (refformat = files, refcount = 1)
Time (mean ± σ): 1.7 ms ± 0.1 ms [User: 0.4 ms, System: 1.2 ms]
Range (min … max): 1.6 ms … 2.1 ms 316 runs
Benchmark 2: update-ref: delete ref (refformat = reftable, refcount = 1)
Time (mean ± σ): 1.8 ms ± 0.1 ms [User: 0.4 ms, System: 1.3 ms]
Range (min … max): 1.7 ms … 2.1 ms 294 runs
Benchmark 3: update-ref: delete ref (refformat = files, refcount = 1000)
Time (mean ± σ): 2.0 ms ± 0.1 ms [User: 0.5 ms, System: 1.4 ms]
Range (min … max): 1.9 ms … 2.5 ms 287 runs
Benchmark 4: update-ref: delete ref (refformat = reftable, refcount = 1000)
Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.5 ms, System: 1.3 ms]
Range (min … max): 1.8 ms … 2.1 ms 217 runs
Benchmark 5: update-ref: delete ref (refformat = files, refcount = 1000000)
Time (mean ± σ): 229.8 ms ± 7.9 ms [User: 182.6 ms, System: 46.8 ms]
Range (min … max): 224.6 ms … 245.2 ms 6 runs
Benchmark 6: update-ref: delete ref (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 2.0 ms ± 0.0 ms [User: 0.6 ms, System: 1.3 ms]
Range (min … max): 2.0 ms … 2.1 ms 3 runs
- Listing all refs shows no significant advantage for either of the
backends. The "files" backend is a bit faster, but not by a
significant margin. When repositories are not packed the "reftable"
backend outperforms the "files" backend because the "reftable"
backend performs auto-compaction.
Benchmark 1: show-ref: print all refs (refformat = files, refcount = 1, packed = true)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.0 ms 1729 runs
Benchmark 2: show-ref: print all refs (refformat = reftable, refcount = 1, packed = true)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 1.8 ms 1816 runs
Benchmark 3: show-ref: print all refs (refformat = files, refcount = 1000, packed = true)
Time (mean ± σ): 4.3 ms ± 0.1 ms [User: 0.9 ms, System: 3.3 ms]
Range (min … max): 4.1 ms … 4.6 ms 645 runs
Benchmark 4: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = true)
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.0 ms, System: 3.3 ms]
Range (min … max): 4.2 ms … 5.9 ms 643 runs
Benchmark 5: show-ref: print all refs (refformat = files, refcount = 1000000, packed = true)
Time (mean ± σ): 2.537 s ± 0.034 s [User: 0.488 s, System: 2.048 s]
Range (min … max): 2.511 s … 2.627 s 10 runs
Benchmark 6: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = true)
Time (mean ± σ): 2.712 s ± 0.017 s [User: 0.653 s, System: 2.059 s]
Range (min … max): 2.692 s … 2.752 s 10 runs
Benchmark 7: show-ref: print all refs (refformat = files, refcount = 1, packed = false)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 1.9 ms 1834 runs
Benchmark 8: show-ref: print all refs (refformat = reftable, refcount = 1, packed = false)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 2.0 ms 1840 runs
Benchmark 9: show-ref: print all refs (refformat = files, refcount = 1000, packed = false)
Time (mean ± σ): 13.8 ms ± 0.2 ms [User: 2.8 ms, System: 10.8 ms]
Range (min … max): 13.3 ms … 14.5 ms 208 runs
Benchmark 10: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = false)
Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.2 ms, System: 3.3 ms]
Range (min … max): 4.3 ms … 6.2 ms 624 runs
Benchmark 11: show-ref: print all refs (refformat = files, refcount = 1000000, packed = false)
Time (mean ± σ): 12.127 s ± 0.129 s [User: 2.675 s, System: 9.451 s]
Range (min … max): 11.965 s … 12.370 s 10 runs
Benchmark 12: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = false)
Time (mean ± σ): 2.799 s ± 0.022 s [User: 0.735 s, System: 2.063 s]
Range (min … max): 2.769 s … 2.836 s 10 runs
- Printing a single ref shows no real difference between the "files"
and "reftable" backends.
Benchmark 1: show-ref: print single ref (refformat = files, refcount = 1)
Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.4 ms, System: 1.0 ms]
Range (min … max): 1.4 ms … 1.8 ms 1779 runs
Benchmark 2: show-ref: print single ref (refformat = reftable, refcount = 1)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 2.5 ms 1753 runs
Benchmark 3: show-ref: print single ref (refformat = files, refcount = 1000)
Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.3 ms, System: 1.1 ms]
Range (min … max): 1.4 ms … 1.9 ms 1840 runs
Benchmark 4: show-ref: print single ref (refformat = reftable, refcount = 1000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.0 ms 1831 runs
Benchmark 5: show-ref: print single ref (refformat = files, refcount = 1000000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.1 ms 1848 runs
Benchmark 6: show-ref: print single ref (refformat = reftable, refcount = 1000000)
Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms]
Range (min … max): 1.5 ms … 2.1 ms 1762 runs
So overall, performance depends on the usecases. Except for many
sequential writes the "reftable" backend is roughly on par or
significantly faster than the "files" backend though. Given that the
"files" backend has received 18 years of optimizations by now this can
be seen as a win. Furthermore, we can expect that the "reftable" backend
will grow faster over time when attention turns more towards
optimizations.
The complete test suite passes, except for those tests explicitly marked
to require the REFFILES prerequisite. Some tests in t0610 are marked as
failing because they depend on still-in-flight bug fixes. Tests can be
run with the new backend by setting the GIT_TEST_DEFAULT_REF_FORMAT
environment variable to "reftable".
There is a single known conceptual incompatibility with the dumb HTTP
transport. As "info/refs" SHOULD NOT contain the HEAD reference, and
because the "HEAD" file is not valid anymore, it is impossible for the
remote client to figure out the default branch without changing the
protocol. This shortcoming needs to be handled in a subsequent patch
series.
As the reftable library has already been introduced a while ago, this
commit message will not go into the details of how exactly the on-disk
format works. Please refer to our preexisting technical documentation at
Documentation/technical/reftable for this.
[1]: https://public-inbox.org/git/CAJo=hJtyof=HRy=2sLP0ng0uZ4=S-DpZ5dR1aF+VHVETKG20OQ@mail.gmail.com/
Original-idea-by: Shawn Pearce <spearce@spearce.org>
Based-on-patch-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Define "special ref" as a very narrow set that consists of
FETCH_HEAD and MERGE_HEAD, and clarify everything else that used to
be classified as such are actually just pseudorefs.
* ps/not-so-many-refs-are-special:
Documentation: add "special refs" to the glossary
refs: redefine special refs
refs: convert MERGE_AUTOSTASH to become a normal pseudo-ref
sequencer: introduce functions to handle autostashes via refs
refs: convert AUTO_MERGE to become a normal pseudo-ref
sequencer: delete REBASE_HEAD in correct repo when picking commits
sequencer: clean up pseudo refs with REF_NO_DEREF
Instead of manually creating refs/ hierarchy on disk upon a
creation of a secondary worktree, which is only usable via the
files backend, use the refs API to populate it.
* ps/worktree-refdb-initialization:
builtin/worktree: create refdb via ref backend
worktree: expose interface to look up worktree by name
builtin/worktree: move setup of commondir file earlier
refs/files: skip creation of "refs/{heads,tags}" for worktrees
setup: move creation of "refs/" into the files backend
refs: prepare `refs_init_db()` for initializing worktree refs
Now that our list of special refs really only contains refs which have
actually-special semantics, let's redefine what makes a special ref.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Similar to the preceding conversion of the AUTO_MERGE pseudo-ref, let's
convert the MERGE_AUTOSTASH ref to become a normal pseudo-ref as well.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In 70c70de616 (refs: complete list of special refs, 2023-12-14) we have
inrtoduced a new `is_special_ref()` function that classifies some refs
as being special. The rule is that special refs are exclusively read and
written via the filesystem directly, whereas normal refs exclucsively go
via the refs API.
The intent of that commit was to record the status quo so that we know
to route reads of such special refs consistently. Eventually, the list
should be reduced to its bare minimum of refs which really are special,
namely FETCH_HEAD and MERGE_HEAD.
Follow up on this promise and convert the AUTO_MERGE ref to become a
normal pseudo-ref by using the refs API to both read and write it
instead of accessing the filesystem directly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Introduce a new extension "refstorage" so that we can mark a
repository that uses a non-default ref backend, like reftable.
* ps/refstorage-extension:
t9500: write "extensions.refstorage" into config
builtin/clone: introduce `--ref-format=` value flag
builtin/init: introduce `--ref-format=` value flag
builtin/rev-parse: introduce `--show-ref-format` flag
t: introduce GIT_TEST_DEFAULT_REF_FORMAT envvar
setup: introduce GIT_DEFAULT_REF_FORMAT envvar
setup: introduce "extensions.refStorage" extension
setup: set repository's formats on init
setup: start tracking ref storage format
refs: refactor logic to look up storage backends
worktree: skip reading HEAD when repairing worktrees
t: introduce DEFAULT_REPO_FORMAT prereq
The purpose of `refs_init_db()` is to initialize the on-disk files of a
new ref database. The function is quite inflexible right now though, as
callers can neither specify the `struct ref_store` nor can they pass any
flags.
Refactor the interface to accept both of these. This will be required so
that we can start initializing per-worktree ref databases via the ref
backend instead of open-coding the initialization in "worktree.c".
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
