expire_reflog(): it's not an each_ref_fn anymore

Prior to v1.5.4~14, expire_reflog() had to be an each_ref_fn because
it was passed to for_each_reflog(). Since then, there has been no
reason for it to implement the each_ref_fn interface. So...

* Remove the "unused" parameter (which took the place of "flags", but
  was really unused).

* Declare the last parameter to be (struct cmd_reflog_expire_cb *)
  rather than (void *).

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): rename "ref" parameter to "refname"

This is our usual convention.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
expire_reflog(): return early if the reference has no reflog

There is very little cleanup needed if the reference has no reflog. If
we move the initialization of log_file down a bit, there's even less.
So instead of jumping to the cleanup code at the end of the function,
just do the cleanup and return inline.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): use a lock_file for rewriting the reflog file

We don't actually need the locking functionality, because we already
hold the lock on the reference itself, which is how the reflog file is
locked. But the lock_file code can do some of the bookkeeping for us,
and it is more careful than the old code here was. For example:

* It correctly handles the case that the reflog lock file already
  exists for some reason or cannot be opened.

* It correctly cleans up the lockfile if the program dies.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Extract function should_expire_reflog_ent()

Extract from expire_reflog_ent() a function that is solely responsible
for deciding whether a reflog entry should be expired. By separating
this "business logic" from the mechanics of actually expiring entries,
we are working towards the goal of encapsulating reflog expiry within
the refs API, with policy decided by a callback function passed to it
by its caller.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): extract two policy-related functions

Extract two functions, reflog_expiry_prepare() and
reflog_expiry_cleanup(), from expire_reflog(). This is a further step
towards separating the code for deciding on expiration policy from the
code that manages the physical deletion of reflog entries.

This change requires a couple of local variables from expire_reflog()
to be turned into fields of "struct expire_reflog_cb". More
reorganization of the callback data will follow in later commits.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): add a "flags" argument

We want to separate the options relevant to the expiry machinery from
the options affecting the expiration policy. So add a "flags" argument
to expire_reflog() to hold the former.

The argument doesn't yet do anything.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): move dry_run to flags argument

The policy objects don't care about "--dry-run". So move it to
expire_reflog()'s flags parameter.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): move updateref to flags argument

The policy objects don't care about "--updateref". So move it to
expire_reflog()'s flags parameter.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Rename expire_reflog_cb to expire_reflog_policy_cb

This is the first step towards separating the data needed by the
policy code from the data needed by the reflog expiration machinery.

(In a moment we will add a *new* "struct expire_reflog_cb" for the use
of expire_reflog() itself, then move fields selectively from
expire_reflog_policy_cb to expire_reflog_cb.)

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
struct expire_reflog_cb: a new callback data type

Add a new data type, "struct expire_reflog_cb", for holding the data
that expire_reflog() passes to expire_reflog_ent() via
for_each_reflog_ent(). For now it only holds a pointer to a "struct
expire_reflog_policy_cb", which still contains all of the actual data.
In future commits we will move some fields from the latter to the
former.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): pass flags through to expire_reflog_ent()

Add a flags field to "struct expire_reflog_cb", and pass the flags
argument through to expire_reflog_ent(). In a moment we will start
using it to pass through flags that expire_reflog_ent() needs.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): move verbose to flags argument

The policy objects don't care about "--verbose". So move it to
expire_reflog()'s flags parameter.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): move rewrite to flags argument

The policy objects don't care about "--rewrite". So move it to
expire_reflog()'s flags parameter.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
Move newlog and last_kept_sha1 to "struct expire_reflog_cb"

These members are not needed by the policy functions.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
expire_reflog(): treat the policy callback data as opaque

Now that expire_reflog() doesn't actually look in the
expire_reflog_policy_cb data structure, we can make it opaque:

* Change the callers of expire_reflog() to pass it a pointer to an
  entire "struct expire_reflog_policy_cb" rather than a pointer to a
  "struct cmd_reflog_expire_cb".

* Change expire_reflog() to accept the argument as a "void *" and
  simply pass it through to the policy functions.

* Change the policy functions, reflog_expiry_prepare(),
  reflog_expiry_cleanup(), and should_expire_reflog_ent(), to accept
  "void *cb_data" arguments and cast them back to "struct
  expire_reflog_policy_cb" internally.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
reflog_expire(): new function in the reference API

Move expire_reflog() into refs.c and rename it to reflog_expire().
Turn the three policy functions into function pointers that are passed
into reflog_expire(). Add function prototypes and documentation to
refs.h.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
refs.c: remove unlock_ref/close_ref/commit_ref from the refs api

unlock|close|commit_ref can be made static since there are no more external
callers.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
lock_any_ref_for_update(): inline function

Inline the function at its one remaining caller (which is within
refs.c) and remove it.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Reviewed-by: Stefan Beller <sbeller@google.com>
refs.c: don't expose the internal struct ref_lock in the header file

Now the struct ref_lock is used completely internally, so let's
remove it from the header file.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>