Merge branch 'tb/pack-revindex-on-disk'

Introduce an on-disk file to record revindex for packdata, which
traditionally was always created on the fly and only in-core.

* tb/pack-revindex-on-disk:
  t5325: check both on-disk and in-memory reverse index
  pack-revindex: ensure that on-disk reverse indexes are given precedence
  t: support GIT_TEST_WRITE_REV_INDEX
  t: prepare for GIT_TEST_WRITE_REV_INDEX
  Documentation/config/pack.txt: advertise 'pack.writeReverseIndex'
  builtin/pack-objects.c: respect 'pack.writeReverseIndex'
  builtin/index-pack.c: write reverse indexes
  builtin/index-pack.c: allow stripping arbitrary extensions
  pack-write.c: prepare to write 'pack-*.rev' files
  packfile: prepare for the existence of '*.rev' files

1 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt
index 96d2fc589f..8833b71c8b 100644
--- a/Documentation/technical/pack-format.txt
+++ b/Documentation/technical/pack-format.txt
@@ -274,6 +274,26 @@ Pack file entry: <+
 
     Index checksum of all of the above.
 
+== pack-*.rev files have the format:
+
+  - A 4-byte magic number '0x52494458' ('RIDX').
+
+  - A 4-byte version identifier (= 1).
+
+  - A 4-byte hash function identifier (= 1 for SHA-1, 2 for SHA-256).
+
+  - A table of index positions (one per packed object, num_objects in
+    total, each a 4-byte unsigned integer in network order), sorted by
+    their corresponding offsets in the packfile.
+
+  - A trailer, containing a:
+
+    checksum of the corresponding packfile, and
+
+    a checksum of all of the above.
+
+All 4-byte numbers are in network order.
+
 == multi-pack-index (MIDX) files have the following format:
 
 The multi-pack-index files refer to multiple pack-files and loose objects.