Merge branch 'nd/split-index'

An experiment to use two files (the base file and incremental
changes relative to it) to represent the index to reduce I/O cost
of rewriting a large index when only small part of the working tree
changes.

* nd/split-index: (32 commits)
  t1700: new tests for split-index mode
  t2104: make sure split index mode is off for the version test
  read-cache: force split index mode with GIT_TEST_SPLIT_INDEX
  read-tree: note about dropping split-index mode or index version
  read-tree: force split-index mode off on --index-output
  rev-parse: add --shared-index-path to get shared index path
  update-index --split-index: do not split if $GIT_DIR is read only
  update-index: new options to enable/disable split index mode
  split-index: strip pathname of on-disk replaced entries
  split-index: do not invalidate cache-tree at read time
  split-index: the reading part
  split-index: the writing part
  read-cache: mark updated entries for split index
  read-cache: save deleted entries in split index
  read-cache: mark new entries for split index
  read-cache: split-index mode
  read-cache: save index SHA-1 after reading
  entry.c: update cache_changed if refresh_cache is set in checkout_entry()
  cache-tree: mark istate->cache_changed on prime_cache_tree()
  cache-tree: mark istate->cache_changed on cache tree update
  ...

1 files changed, 26 insertions, 7 deletions

diff --git a/builtin/update-index.c b/builtin/update-index.c
index ebea285e1..e8c7fd4d4 100644
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -13,6 +13,7 @@
 #include "parse-options.h"
 #include "pathspec.h"
 #include "dir.h"
+#include "split-index.h"
 
 /*
  * Default to not allowing changes to the list of files. The
@@ -55,8 +56,9 @@ static int mark_ce_flags(const char *path, int flag, int mark)
 			active_cache[pos]->ce_flags |= flag;
 		else
 			active_cache[pos]->ce_flags &= ~flag;
-		cache_tree_invalidate_path(active_cache_tree, path);
-		active_cache_changed = 1;
+		active_cache[pos]->ce_flags |= CE_UPDATE_IN_BASE;
+		cache_tree_invalidate_path(&the_index, path);
+		active_cache_changed |= CE_ENTRY_CHANGED;
 		return 0;
 	}
 	return -1;
@@ -267,8 +269,9 @@ static void chmod_path(int flip, const char *path)
 	default:
 		goto fail;
 	}
-	cache_tree_invalidate_path(active_cache_tree, path);
-	active_cache_changed = 1;
+	cache_tree_invalidate_path(&the_index, path);
+	ce->ce_flags |= CE_UPDATE_IN_BASE;
+	active_cache_changed |= CE_ENTRY_CHANGED;
 	report("chmod %cx '%s'", flip, path);
 	return;
  fail:
@@ -743,6 +746,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 	char set_executable_bit = 0;
 	struct refresh_params refresh_args = {0, &has_errors};
 	int lock_error = 0;
+	int split_index = -1;
 	struct lock_file *lock_file;
 	struct parse_opt_ctx_t ctx;
 	int parseopt_state = PARSE_OPT_UNKNOWN;
@@ -825,6 +829,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			resolve_undo_clear_callback},
 		OPT_INTEGER(0, "index-version", &preferred_index_format,
 			N_("write index in this format")),
+		OPT_BOOL(0, "split-index", &split_index,
+			N_("enable or disable split index")),
 		OPT_END()
 	};
 
@@ -892,7 +898,7 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 			    INDEX_FORMAT_LB, INDEX_FORMAT_UB);
 
 		if (the_index.version != preferred_index_format)
-			active_cache_changed = 1;
+			active_cache_changed |= SOMETHING_CHANGED;
 		the_index.version = preferred_index_format;
 	}
 
@@ -918,14 +924,27 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
 		strbuf_release(&buf);
 	}
 
+	if (split_index > 0) {
+		init_split_index(&the_index);
+		the_index.cache_changed |= SPLIT_INDEX_ORDERED;
+	} else if (!split_index && the_index.split_index) {
+		/*
+		 * can't discard_split_index(&the_index); because that
+		 * will destroy split_index->base->cache[], which may
+		 * be shared with the_index.cache[]. So yeah we're
+		 * leaking a bit here.
+		 */
+		the_index.split_index = NULL;
+		the_index.cache_changed |= SOMETHING_CHANGED;
+	}
+
 	if (active_cache_changed) {
 		if (newfd < 0) {
 			if (refresh_args.flags & REFRESH_QUIET)
 				exit(128);
 			unable_to_lock_index_die(get_index_file(), lock_error);
 		}
-		if (write_cache(newfd, active_cache, active_nr) ||
-		    commit_locked_index(lock_file))
+		if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
 			die("Unable to write new index file");
 	}