The initialization of the on-disk state of refdbs is currently not
handled by the actual refdb backend, but it's implemented ad-hoc where
needed. This is problematic once we have multiple different refdbs as
the filesystem structure is of course not the same.
Introduce a new callback function `git_refdb_backend::init()`. If set,
this callback can be invoked via `git_refdb_init()` to initialize the
on-disk state of a refdb. Like this, each backend can decide for itself
how exactly to do this.
Note that the initialization of the refdb is a bit intricate. A
repository is only recognized as such when it has a "HEAD" file as well
as a "refs/" directory. Consequently, regardless of which refdb format
we use, those files must always be present. This also proves to be
problematic for us, as we cannot access the repository and thus don't
have access to the refdb if those files didn't exist.
To work around the issue we thus handle the creation of those files
outside of the refdb-specific logic. We actually use the same strategy
as Git does, and write the invalid reference "ref: refs/heads/.invalid"
into "HEAD". This looks almost like a ref, but the name of that ref
is not valid and should thus trip up Git clients that try to read that
ref in a repository that really uses a different format.
So while that invalid "HEAD" reference will of course get rewritten by
the "files" backend, other backends should just retain it as-is.
The callbacks are currently sparsely documented, making it really hard
to implement a new backend without taking a look at the existing
refdb_fs backend. Add documentation to make this task hopefully easier
to achieve.
Since we now always build the library with cdecl calling conventions,
our callbacks should be decorated as such so that users will not be able
to provide callbacks defined with other calling conventions.
The `GIT_CALLBACK` macro will inject the `__cdecl` attribute as
appropriate.
As refdb and odb backends can be allocated by client code, libgit2
can’t know whether an alternative memory allocator was used, and thus
should not try to call `git__free` on those objects.
Instead, odb and refdb backend implementations must always provide
their own `free` functions to ensure memory gets freed correctly.
Removing a reflog upon ref deletion is something which only some
backends might wish to do. Backends which are database-backed may wish
to archive a reflog, log-based ones may not need to do anything.
A transaction allows you to lock multiple references and set up changes
for them before applying the changes all at once (or as close as the
backend supports).
This can be used for replication purposes, or for making sure some
operations run when the reference is locked and thus cannot be changed.
The frontend used to look at the file directly, but that's obviously not
the right thing to do. Expose it on the backend and use that function
instead.
Whenever a reference is created or updated, we need to write to the
reflog regardless of whether the user gave us a message, so we shouldn't
leave that to the ref frontend, but integrate it into the backend.
This also eliminates the race between ref update and writing to the
reflog, as we protect the reflog with the ref lock.
As an additional benefit, this reflog append on the backend happens by
appending to the file instead of parsing and rewriting it.
References and their logs are logically coupled, let's make it so in
the code by moving the fs-based reflog implementation to live next to
the fs-based refs one.
As part of the change, make the function take names rather than
references, as only the names are relevant when looking up and
handling reflogs.
Nobody should ever be using anything other than ALL at this level, so
remove the option altogether.
As part of this, git_reference_foreach_glob is now implemented in the
frontend using an iterator. Backends will later regain the ability of
doing the glob filtering in the backend.
This moves most of the refdb stuff over to the include/git2/sys
directory, with some minor shifts in function organization.
While I was making the necessary updates, I also removed the
trailing whitespace in a few files that I modified just because I
was there and it was bugging me.
