Merge branch 'jc/index-v4'

Trivially shrinks the on-disk size of the index file to save both I/O and
checksum overhead.

The topic should give a solid base to build on further updates, with the
code refactoring in its earlier parts, and the backward compatibility
mechanism in its later parts.

* jc/index-v4:
  index-v4: document the entry format
  unpack-trees: preserve the index file version of original
  update-index: upgrade/downgrade on-disk index version
  read-cache.c: write prefix-compressed names in the index
  read-cache.c: read prefix-compressed names in index on-disk version v4
  read-cache.c: move code to copy incore to ondisk cache to a helper function
  read-cache.c: move code to copy ondisk to incore cache to a helper function
  read-cache.c: report the header version we do not understand
  read-cache.c: make create_from_disk() report number of bytes it consumed
  read-cache.c: allow unaligned mapping of the index file
  cache.h: hide on-disk index details
  varint: make it available outside the context of pack

1 files changed, 14 insertions, 0 deletions

diff --git a/builtin/update-index.c b/builtin/update-index.c
index a6a23fa1f..5f038d64d 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -708,6 +708,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	int newfd, entries, has_errors = 0, line_termination = '\n';
 	int read_from_stdin = 0;
 	int prefix_length = prefix ? strlen(prefix) : 0;
+	int preferred_index_format = 0;
 	char set_executable_bit = 0;
 	struct refresh_params refresh_args = {0, &has_errors};
 	int lock_error = 0;
@@ -791,6 +792,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			"(for porcelains) forget saved unresolved conflicts",
 			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
 			resolve_undo_clear_callback},
+		OPT_INTEGER(0, "index-version", &preferred_index_format,
+			    "write index in this format"),
 		OPT_END()
 	};
 
@@ -851,6 +854,17 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		}
 	}
 	argc = parse_options_end(&ctx);
+	if (preferred_index_format) {
+		if (preferred_index_format < INDEX_FORMAT_LB ||
+		    INDEX_FORMAT_UB < preferred_index_format)
+			die("index-version %d not in range: %d..%d",
+			    preferred_index_format,
+			    INDEX_FORMAT_LB, INDEX_FORMAT_UB);
+
+		if (the_index.version != preferred_index_format)
+			active_cache_changed = 1;
+		the_index.version = preferred_index_format;
+	}
 
 	if (read_from_stdin) {
 		struct strbuf buf = STRBUF_INIT, nbuf = STRBUF_INIT;