Merge branch 'np/pack' into next

* np/pack:
  git-repack: repo.usedeltabaseoffset
  pack-objects: document --delta-base-offset option

Documentation/config.txt

@@ -234,6 +234,10 @@ pull.octopus::
 pull.twohead::
 	The default merge strategy to use when pulling a single branch.
 
+repack.usedeltabaseoffset::
+	Allow gitlink:git-repack[1] to create packs that uses
+	delta-base offset.  Defaults to false.
+
 show.difftree::
 	The default gitlink:git-diff-tree[1] arguments to be used
 	for gitlink:git-show[1].

Documentation/git-pack-objects.txt

@@ -9,7 +9,7 @@ git-pack-objects - Create a packed archive of objects
 SYNOPSIS
 --------
 [verse]
-'git-pack-objects' [-q] [--no-reuse-delta] [--non-empty]
+'git-pack-objects' [-q] [--no-reuse-delta] [--delta-base-offset] [--non-empty]
 	[--local] [--incremental] [--window=N] [--depth=N]
 	[--revs [--unpacked | --all]*] [--stdout | base-name] < object-list
 
@@ -111,6 +111,17 @@ base-name::
 	This flag tells the command not to reuse existing deltas
 	but compute them from scratch.
 
+--delta-base-offset::
+	A packed archive can express base object of a delta as
+	either 20-byte object name or as an offset in the
+	stream, but older version of git does not understand the
+	latter.  By default, git-pack-objects only uses the
+	former format for better compatibility.  This option
+	allows the command to use the latter format for
+	compactness.  Depending on the average delta chain
+	length, this option typically shrinks the resulting
+	packfile by 3-5 per-cent.
+
 
 Author
 ------

Documentation/git-repack.txt

@@ -67,6 +67,20 @@ OPTIONS
 	The default value for both --window and --depth is 10.
 
 
+Configuration
+-------------
+
+When configuration variable `repack.UseDeltaBaseOffset` is set
+for the repository, the command passes `--delta-base-offset`
+option to `git-pack-objects`; this typically results in slightly
+smaller packs, but the generated packs are incompatible with
+versions of git older than (and including) v1.4.3; do not set
+the variable in a repository that older version of git needs to
+be able to read (this includes repositories from which packs can
+be copied out over http or rsync, and people who obtained packs
+that way can try to use older git with it).
+
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>

builtin-pack-objects.c

@@ -15,7 +15,7 @@
 #include <sys/time.h>
 #include <signal.h>
 
-static const char pack_usage[] = "git-pack-objects [-q] [--no-reuse-delta] [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] [--revs [--unpacked | --all]*] [--stdout | base-name] <ref-list | <object-list]";
+static const char pack_usage[] = "git-pack-objects [-q] [--no-reuse-delta] [--delta-base-offset] [--non-empty] [--local] [--incremental] [--window=N] [--depth=N] [--revs [--unpacked | --all]*] [--stdout | base-name] <ref-list | <object-list]";
 
 struct object_entry {
 	unsigned char sha1[20];

git-repack.sh

@@ -3,7 +3,7 @@
 # Copyright (c) 2005 Linus Torvalds
 #
 
-USAGE='[-a] [-d] [-f] [-l] [-n] [-q]'
+USAGE='[-a] [-d] [-f] [-l] [-n] [-q] [--window=N] [--depth=N]'
 SUBDIRECTORY_OK='Yes'
 . git-sh-setup
 
@@ -25,6 +25,15 @@ do
 	shift
 done
 
+# Later we will default repack.UseDeltaBaseOffset to true
+default_dbo=false
+
+case "`git repo-config --bool repack.usedeltabaseoffset ||
+       echo $default_dbo`" in
+true)
+	extra="$extra --delta-base-offset" ;;
+esac
+
 PACKDIR="$GIT_OBJECT_DIRECTORY/pack"
 PACKTMP="$GIT_DIR/.tmp-$$-pack"
 rm -f "$PACKTMP"-*