[PATCH v3 00/21] Read `packed-refs` using mmap()

This is v3 of a patch series that changes the reading and caching of the `packed-refs` file to use `mmap()`. Thanks to Stefan, Peff, Dscho, and Junio for their comments about v2. I think I have addressed all of the feedback from v1 [1] and v2 [2].

This version has only minor changes relative to v2:

* Fixed a trivial error in the commit message for patch 08.

* In patch 13:

  * In the commit message, explain the appearance of `MMAP_TEMPORARY`
    even though it is not yet treated differently than `MMAP_NONE`.

  * In `Makefile`, don't make `USE_WIN32_MMAP` imply
    `MMAP_PREVENTS_DELETE`.

  * Correct the type of a local variable from `size_t` to `ssize_t`.

This patch series is also available from my GitHub repo [3] as branch `mmap-packed-refs`.

[1] http://public-inbox.org/git/cover.1505319366.git.mhagger@alum.mit.edu/ [2] https://public-inbox.org/git/cover.1505799700.git.mhagger@alum.mit.edu/ [3] https://github.com/mhagger/git/

Jeff King (1):
  prefix_ref_iterator: break when we leave the prefix

Michael Haggerty (20):
  ref_iterator: keep track of whether the iterator output is ordered
  packed_ref_cache: add a backlink to the associated `packed_ref_store`
  die_unterminated_line(), die_invalid_line(): new functions
  read_packed_refs(): use mmap to read the `packed-refs` file
  read_packed_refs(): only check for a header at the top of the file
  read_packed_refs(): make parsing of the header line more robust
  read_packed_refs(): read references with minimal copying
  packed_ref_cache: remember the file-wide peeling state
  mmapped_ref_iterator: add iterator over a packed-refs file
  mmapped_ref_iterator_advance(): no peeled value for broken refs
  packed-backend.c: reorder some definitions
  packed_ref_cache: keep the `packed-refs` file mmapped if possible
  read_packed_refs(): ensure that references are ordered when read
  packed_ref_iterator_begin(): iterate using `mmapped_ref_iterator`
  packed_read_raw_ref(): read the reference from the mmapped buffer
  ref_store: implement `refs_peel_ref()` generically
  packed_ref_store: get rid of the `ref_cache` entirely
  ref_cache: remove support for storing peeled values
  mmapped_ref_iterator: inline into `packed_ref_iterator`
  packed-backend.c: rename a bunch of things and update comments

 Makefile              |   6 +
 config.mak.uname      |   3 +
 refs.c                |  22 +-
 refs/files-backend.c  |  54 +--
 refs/iterator.c       |  47 ++-
 refs/packed-backend.c | 979 ++++++++++++++++++++++++++++++++++++++------------
 refs/ref-cache.c      |  44 +--
 refs/ref-cache.h      |  35 +-
 refs/refs-internal.h  |  26 +-
 9 files changed, 847 insertions(+), 369 deletions(-)