refs.c: allow passing raw git_committer_info as email to _update_reflog

In many places in the code we do not have access to the individual fields
in the committer data. Instead we might only have access to prebaked data
such as what is returned by git_committer_info() containing a string
that consists of email, timestamp, zone etc.

This makes it inconvenient to use transaction_update_reflog since it means
you would have to first parse git_committer_info before you can call
update_reflog.

Add a new flag REFLOG_COMMITTER_INFO_IS_VALID to _update_reflog to tell it
that we pass in a fully prebaked committer info string that can be used as is.

At the same time, also go over and change all references from email
to id where the code actually refers to a committer id and not just an email
address. I.e. where the string is : NAME <EMAIL>

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
refs.c: return error instead of dying when locking fails during transaction

Change lock_ref_sha1_basic to return an error instead of dying when
we fail to lock a file during a transaction.
This function is only called from transaction_commit() and it knows how
to handle these failures.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
refs.c: use packed refs when deleting refs during a transaction

Make the deletion of refs during a transaction more atomic.
Start by first copying all loose refs we will be deleting to the packed
refs file and then commit the packed refs file. Then re-lock the packed refs
file to stop anyone else from modifying these refs and keep it locked until
we are finished.
Since all refs we are about to delete are now safely held in the packed refs
file we can proceed to immediately unlink any corresponding loose refs
and still be fully rollback-able.

The exception is for refs that can not be resolved. Those refs are never
added to the packed refs and will just be un-rollback-ably deleted during
commit.

By deleting all the loose refs at the start of the transaction we make make
it possible to both delete one ref and then re-create a different ref in
the same transaction even if the two refs would normally conflict.

Example: rename m->m/m

In that example we want to delete the file 'm' so that we make room so
that we can create a directory with the same name in order to lock and
write to the ref m/m and its lock-file m/m.lock.

If there is a failure during the commit phase we can rollback without losing
any refs since we have so far only deleted loose refs that that are
guaranteed to also have a corresponding entry in the packed refs file.
Once we have finished all updates for refs and their reflogs we can repack
the packed refs file and remove the to-be-deleted refs from the packed refs,
at which point all the deleted refs will disappear in one atomic rename
operation.

This also means that for an outside observer, deletion of multiple refs
in a single transaction will look atomic instead of one ref being deleted
at a time.

In order to do all this we need to change the semantics for the
repack_without_refs function so that we can lock the packed refs file,
do other stuff, and later be able to call repack_without_refs with the
lock already taken.
This means we need some additional changes in remote.c to reflect the
changes to the repack_without_refs semantics.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
refs.c: update rename_ref to use a transaction

Change refs.c to use a single transaction to copy/rename both the refs and
its reflog. Since we are no longer using rename() to move the reflog file
we no longer need to disallow rename_ref for refs with a symlink for its
reflog so we can remove that test from the testsuite.

Change the function to return 1 on failure instead of either -1 or 1.

These changes make the rename_ref operation atomic. This also eliminates the
need to use rename() to shift the reflog around via a temporary filename.
As an extension to this, since we no longer use rename() on the reflog file,
we can now safely perform renames even if the reflog is a symbolic link
and thus can remove the check and fail for that condition.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
refs.c: rollback the lockfile before we die() in repack_without_refs

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>