[PATCH v2 00/12] Fix some reference-related races

Re-roll of mh/ref-races. Thanks to Peff, Junio, and Ramsay for reviewing v1.

Changes since v1:

* mh/reflife has graduated to master, so this patch series now applies
  directly to master.

* Some trivial constness adjustments were necessary because of

    21a6b9fa read-cache: mark cache_entry pointers const

* Better explain (in comments and log message) patch 01/12.

* In 04/12, access struct lock_file::fd directly instead of keeping
  a separate copy in struct packed_ref_cache.

Please note that this patch series's usage of stat()/fstat() causes breakages under cygwin, pointed out by Ramsay Jones. He has graciously offered to work on this issue.

The last patch is still optional--it avoids a little bit of work when rewriting the packed-refs file, but relies on the stat-based freshness check not giving a false negative.

Jeff King (2):
  get_packed_ref_cache: reload packed-refs file when it changes
  for_each_ref: load all loose refs before packed refs

Michael Haggerty (10):
  repack_without_ref(): split list curation and entry writing
  pack_refs(): split creation of packed refs and entry writing
  refs: wrap the packed refs cache in a level of indirection
  refs: implement simple transactions for the packed-refs file
  refs: manage lifetime of packed refs cache via reference counting
  do_for_each_entry(): increment the packed refs cache refcount
  packed_ref_cache: increment refcount when locked
  Extract a struct stat_data from cache_entry
  add a stat_validity struct
  refs: do not invalidate the packed-refs cache unnecessarily

 builtin/clone.c    |   7 +-
 builtin/ls-files.c |  12 +-
 cache.h            |  60 ++++++++--
 read-cache.c       | 181 ++++++++++++++++++------------
 refs.c             | 314 ++++++++++++++++++++++++++++++++++++++++++++---------
 refs.h             |  27 ++++-
 6 files changed, 469 insertions(+), 132 deletions(-)