[PATCH 0/4] Using transactions for the reflog

This is the core part of the refs-transactions-reflog series[1], which was in discussion for a bit already.

The idea is to have the reflog being part of the transactions, which the refs are already using, so the we're moving towards a database like API in the long run. This makes git easier to maintain as well as opening the possibility to replace the backend with a real database.

The first patch is essentially just some sed magic with reformatting the code, so the naming convention fits better, because the transactions will handle both the refs as well as the reflog after this series.

The second patch introduces a new enum field to indicate, if we deal with a ref or with a reflog entry in the transaction.

The meat and most of the lines of code are found in the 3rd patch. We introduce a rather lengthy function transaction_update_reflog, which prepares all the reflog related changes. The transaction_commit function will then also put the reflog changes in place in a "best effort" atomic way. Unlike in previous versions, we don't keep all the reflog in memory, but use a temporary file in $GIT_DIR instead and the update can be done using an atomic rename(...).

One of my todos is to make the error handling in the transaction_update_reflog function a bit less repetitive either during the discussion of this series or as a follow up.

The last patch in this series makes use of the transaction system in the user facing code, when running "git reflog expire" for example.

I'd appreciate any comments. 

Apart from sending feedback on the list, you can find this series at github[2] embedded into the longer version of the series. In that series at github there are a few more patches[3], which are already reviewed and residing in Junios repository or considered trivial cleanups.

Thanks, Stefan

[1] http://comments.gmane.org/gmane.comp.version-control.git/259712
[2] https://github.com/stefanbeller/git/commits/todo_sb13_ref-transactions-reflog-as-file
[3] The first 2 commits on top of Git 2.2-rc3 are origin/sb/ref-transaction-unify-to-update, 
    the third is in origin/sb/log-ref-write-fd, then comes this series in 4 patches. 
    The remaining latest 4 patches are clean up patches, mainly removing parts from the refs API
    which are no longer in use. I do not include these in this patch series, as I don't want to
    scare people away with a huge bulk of messages.

Ronnie Sahlberg (4):
  refs.c: rename the transaction functions
  refs.c: add a new update_type field to ref_update
  refs.c: add a transaction function to append a reflog entry
  reflog.c: use a reflog transaction when writing during expire

 branch.c               |  13 +--
 builtin/commit.c       |  10 +-
 builtin/fetch.c        |  12 +--
 builtin/receive-pack.c |  13 ++-
 builtin/reflog.c       |  85 ++++++++---------
 builtin/replace.c      |  10 +-
 builtin/tag.c          |  10 +-
 builtin/update-ref.c   |  26 ++---
 fast-import.c          |  22 ++---
 refs.c                 | 251 ++++++++++++++++++++++++++++++++++++++++---------
 refs.h                 |  57 +++++++----
 sequencer.c            |  12 +--
 walker.c               |  10 +-
 13 files changed, 352 insertions(+), 179 deletions(-)