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/[email protected]/
[2] https://public-inbox.org/git/[email protected]/
[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(-)

2.14.1