Merge branch 'tb/cruft-packs'

A mechanism to pack unreachable objects into a "cruft pack",
instead of ejecting them into loose form to be reclaimed later, has
been introduced.

* tb/cruft-packs:
  sha1-file.c: don't freshen cruft packs
  builtin/gc.c: conditionally avoid pruning objects via loose
  builtin/repack.c: add cruft packs to MIDX during geometric repack
  builtin/repack.c: use named flags for existing_packs
  builtin/repack.c: allow configuring cruft pack generation
  builtin/repack.c: support generating a cruft pack
  builtin/pack-objects.c: --cruft with expiration
  reachable: report precise timestamps from objects in cruft packs
  reachable: add options to add_unseen_recent_objects_to_traversal
  builtin/pack-objects.c: --cruft without expiration
  builtin/pack-objects.c: return from create_object_entry()
  t/helper: add 'pack-mtimes' test-tool
  pack-mtimes: support writing pack .mtimes files
  chunk-format.h: extract oid_version()
  pack-write: pass 'struct packing_data' to 'stage_tmp_packfiles'
  pack-mtimes: support reading .mtimes files
  Documentation/technical: add cruft-packs.txt

1 files changed, 30 insertions, 0 deletions

diff --git a/Documentation/git-pack-objects.txt b/Documentation/git-pack-objects.txt
index f8344e1e5b..a9995a932c 100644
--- a/Documentation/git-pack-objects.txt
+++ b/Documentation/git-pack-objects.txt
@@ -13,6 +13,7 @@ SYNOPSIS
 	[--no-reuse-delta] [--delta-base-offset] [--non-empty]
 	[--local] [--incremental] [--window=<n>] [--depth=<n>]
 	[--revs [--unpacked | --all]] [--keep-pack=<pack-name>]
+	[--cruft] [--cruft-expiration=<time>]
 	[--stdout [--filter=<filter-spec>] | <base-name>]
 	[--shallow] [--keep-true-parents] [--[no-]sparse] < <object-list>
 
@@ -95,6 +96,35 @@ base-name::
 Incompatible with `--revs`, or options that imply `--revs` (such as
 `--all`), with the exception of `--unpacked`, which is compatible.
 
+--cruft::
+	Packs unreachable objects into a separate "cruft" pack, denoted
+	by the existence of a `.mtimes` file. Typically used by `git
+	repack --cruft`. Callers provide a list of pack names and
+	indicate which packs will remain in the repository, along with
+	which packs will be deleted (indicated by the `-` prefix). The
+	contents of the cruft pack are all objects not contained in the
+	surviving packs which have not exceeded the grace period (see
+	`--cruft-expiration` below), or which have exceeded the grace
+	period, but are reachable from an other object which hasn't.
++
+When the input lists a pack containing all reachable objects (and lists
+all other packs as pending deletion), the corresponding cruft pack will
+contain all unreachable objects (with mtime newer than the
+`--cruft-expiration`) along with any unreachable objects whose mtime is
+older than the `--cruft-expiration`, but are reachable from an
+unreachable object whose mtime is newer than the `--cruft-expiration`).
++
+Incompatible with `--unpack-unreachable`, `--keep-unreachable`,
+`--pack-loose-unreachable`, `--stdin-packs`, as well as any other
+options which imply `--revs`. Also incompatible with `--max-pack-size`;
+when this option is set, the maximum pack size is not inferred from
+`pack.packSizeLimit`.
+
+--cruft-expiration=<approxidate>::
+	If specified, objects are eliminated from the cruft pack if they
+	have an mtime older than `<approxidate>`. If unspecified (and
+	given `--cruft`), then no objects are eliminated.
+
 --window=<n>::
 --depth=<n>::
 	These two options affect how the objects contained in