1 files changed, 536 insertions, 157 deletions

diff --git a/read-cache.c b/read-cache.c
index 9054369dd0..977921d90c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -5,6 +5,7 @@
  */
 #define NO_THE_INDEX_COMPATIBILITY_MACROS
 #include "cache.h"
+#include "config.h"
 #include "tempfile.h"
 #include "lockfile.h"
 #include "cache-tree.h"
@@ -18,6 +19,7 @@
 #include "varint.h"
 #include "split-index.h"
 #include "utf8.h"
+#include "fsmonitor.h"
 
 /* Mask for the name length in ce_flags in the on-disk index */
 
@@ -37,11 +39,12 @@
 #define CACHE_EXT_RESOLVE_UNDO 0x52455543 /* "REUC" */
 #define CACHE_EXT_LINK 0x6c696e6b	  /* "link" */
 #define CACHE_EXT_UNTRACKED 0x554E5452	  /* "UNTR" */
+#define CACHE_EXT_FSMONITOR 0x46534D4E	  /* "FSMN" */
 
 /* changes that can be kept in $GIT_DIR/index (basically all extensions) */
 #define EXTMASK (RESOLVE_UNDO_CHANGED | CACHE_TREE_CHANGED | \
 		 CE_ENTRY_ADDED | CE_ENTRY_REMOVED | CE_ENTRY_CHANGED | \
-		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED)
+		 SPLIT_INDEX_ORDERED | UNTRACKED_CHANGED | FSMONITOR_CHANGED)
 
 struct index_state the_index;
 static const char *alternate_index_output;
@@ -61,25 +64,26 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 	free(old);
 	set_index_entry(istate, nr, ce);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
+	mark_fsmonitor_invalid(istate, ce);
 	istate->cache_changed |= CE_ENTRY_CHANGED;
 }
 
 void rename_index_entry_at(struct index_state *istate, int nr, const char *new_name)
 {
-	struct cache_entry *old = istate->cache[nr], *new;
+	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
 	int namelen = strlen(new_name);
 
-	new = xmalloc(cache_entry_size(namelen));
-	copy_cache_entry(new, old);
-	new->ce_flags &= ~CE_HASHED;
-	new->ce_namelen = namelen;
-	new->index = 0;
-	memcpy(new->name, new_name, namelen + 1);
+	new_entry = xmalloc(cache_entry_size(namelen));
+	copy_cache_entry(new_entry, old_entry);
+	new_entry->ce_flags &= ~CE_HASHED;
+	new_entry->ce_namelen = namelen;
+	new_entry->index = 0;
+	memcpy(new_entry->name, new_name, namelen + 1);
 
-	cache_tree_invalidate_path(istate, old->name);
-	untracked_cache_remove_from_index(istate, old->name);
+	cache_tree_invalidate_path(istate, old_entry->name);
+	untracked_cache_remove_from_index(istate, old_entry->name);
 	remove_index_entry_at(istate, nr);
-	add_index_entry(istate, new, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 }
 
 void fill_stat_data(struct stat_data *sd, struct stat *st)
@@ -149,8 +153,10 @@ void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
 	if (assume_unchanged)
 		ce->ce_flags |= CE_VALID;
 
-	if (S_ISREG(st->st_mode))
+	if (S_ISREG(st->st_mode)) {
 		ce_mark_uptodate(ce);
+		mark_fsmonitor_valid(ce);
+	}
 }
 
 static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
@@ -159,9 +165,9 @@ static int ce_compare_data(const struct cache_entry *ce, struct stat *st)
 	int fd = git_open_cloexec(ce->name, O_RDONLY);
 
 	if (fd >= 0) {
-		unsigned char sha1[20];
-		if (!index_fd(sha1, fd, st, OBJ_BLOB, ce->name, 0))
-			match = hashcmp(sha1, ce->oid.hash);
+		struct object_id oid;
+		if (!index_fd(&oid, fd, st, OBJ_BLOB, ce->name, 0))
+			match = oidcmp(&oid, &ce->oid);
 		/* index_fd() closed the file descriptor already */
 	}
 	return match;
@@ -190,7 +196,7 @@ static int ce_compare_link(const struct cache_entry *ce, size_t expected_size)
 
 static int ce_compare_gitlink(const struct cache_entry *ce)
 {
-	unsigned char sha1[20];
+	struct object_id oid;
 
 	/*
 	 * We don't actually require that the .git directory
@@ -200,9 +206,9 @@ static int ce_compare_gitlink(const struct cache_entry *ce)
 	 *
 	 * If so, we consider it always to match.
 	 */
-	if (resolve_gitlink_ref(ce->name, "HEAD", sha1) < 0)
+	if (resolve_gitlink_ref(ce->name, "HEAD", &oid) < 0)
 		return 0;
-	return hashcmp(sha1, ce->oid.hash);
+	return oidcmp(&oid, &ce->oid);
 }
 
 static int ce_modified_check_fs(const struct cache_entry *ce, struct stat *st)
@@ -219,6 +225,7 @@ static int ce_modified_check_fs(const struct cache_entry *ce, struct stat *st)
 	case S_IFDIR:
 		if (S_ISGITLINK(ce->ce_mode))
 			return ce_compare_gitlink(ce) ? DATA_CHANGED : 0;
+		/* else fallthrough */
 	default:
 		return TYPE_CHANGED;
 	}
@@ -299,7 +306,7 @@ int match_stat_data_racy(const struct index_state *istate,
 	return match_stat_data(sd, st);
 }
 
-int ie_match_stat(const struct index_state *istate,
+int ie_match_stat(struct index_state *istate,
 		  const struct cache_entry *ce, struct stat *st,
 		  unsigned int options)
 {
@@ -307,7 +314,10 @@ int ie_match_stat(const struct index_state *istate,
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
 	int assume_racy_is_modified = options & CE_MATCH_RACY_IS_DIRTY;
+	int ignore_fsmonitor = options & CE_MATCH_IGNORE_FSMONITOR;
 
+	if (!ignore_fsmonitor)
+		refresh_fsmonitor(istate);
 	/*
 	 * If it's marked as always valid in the index, it's
 	 * valid whatever the checked-out copy says.
@@ -318,6 +328,8 @@ int ie_match_stat(const struct index_state *istate,
 		return 0;
 	if (!ignore_valid && (ce->ce_flags & CE_VALID))
 		return 0;
+	if (!ignore_fsmonitor && (ce->ce_flags & CE_FSMONITOR_VALID))
+		return 0;
 
 	/*
 	 * Intent-to-add entries have not been added, so the index entry
@@ -355,7 +367,7 @@ int ie_match_stat(const struct index_state *istate,
 	return changed;
 }
 
-int ie_modified(const struct index_state *istate,
+int ie_modified(struct index_state *istate,
 		const struct cache_entry *ce,
 		struct stat *st, unsigned int options)
 {
@@ -514,9 +526,8 @@ int remove_index_entry_at(struct index_state *istate, int pos)
 	istate->cache_nr--;
 	if (pos >= istate->cache_nr)
 		return 0;
-	memmove(istate->cache + pos,
-		istate->cache + pos + 1,
-		(istate->cache_nr - pos) * sizeof(struct cache_entry *));
+	MOVE_ARRAY(istate->cache + pos, istate->cache + pos + 1,
+		   istate->cache_nr - pos);
 	return 1;
 }
 
@@ -604,39 +615,43 @@ static struct cache_entry *create_alias_ce(struct index_state *istate,
 					   struct cache_entry *alias)
 {
 	int len;
-	struct cache_entry *new;
+	struct cache_entry *new_entry;
 
 	if (alias->ce_flags & CE_ADDED)
 		die("Will not add file alias '%s' ('%s' already exists in index)", ce->name, alias->name);
 
 	/* Ok, create the new entry using the name of the existing alias */
 	len = ce_namelen(alias);
-	new = xcalloc(1, cache_entry_size(len));
-	memcpy(new->name, alias->name, len);
-	copy_cache_entry(new, ce);
+	new_entry = xcalloc(1, cache_entry_size(len));
+	memcpy(new_entry->name, alias->name, len);
+	copy_cache_entry(new_entry, ce);
 	save_or_free_index_entry(istate, ce);
-	return new;
+	return new_entry;
 }
 
 void set_object_name_for_intent_to_add_entry(struct cache_entry *ce)
 {
-	unsigned char sha1[20];
-	if (write_sha1_file("", 0, blob_type, sha1))
+	struct object_id oid;
+	if (write_object_file("", 0, blob_type, &oid))
 		die("cannot create an empty blob in the object database");
-	hashcpy(ce->oid.hash, sha1);
+	oidcpy(&ce->oid, &oid);
 }
 
 int add_to_index(struct index_state *istate, const char *path, struct stat *st, int flags)
 {
 	int size, namelen, was_same;
 	mode_t st_mode = st->st_mode;
-	struct cache_entry *ce, *alias;
+	struct cache_entry *ce, *alias = NULL;
 	unsigned ce_option = CE_MATCH_IGNORE_VALID|CE_MATCH_IGNORE_SKIP_WORKTREE|CE_MATCH_RACY_IS_DIRTY;
 	int verbose = flags & (ADD_CACHE_VERBOSE | ADD_CACHE_PRETEND);
 	int pretend = flags & ADD_CACHE_PRETEND;
 	int intent_only = flags & ADD_CACHE_INTENT;
 	int add_option = (ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|
 			  (intent_only ? ADD_CACHE_NEW_ONLY : 0));
+	int newflags = HASH_WRITE_OBJECT;
+
+	if (flags & HASH_RENORMALIZE)
+		newflags |= HASH_RENORMALIZE;
 
 	if (!S_ISREG(st_mode) && !S_ISLNK(st_mode) && !S_ISDIR(st_mode))
 		return error("%s: can only add regular files, symbolic links or git-directories", path);
@@ -677,19 +692,23 @@ int add_to_index(struct index_state *istate, const char *path, struct stat *st,
 	if (ignore_case) {
 		adjust_dirname_case(istate, ce->name);
 	}
+	if (!(flags & HASH_RENORMALIZE)) {
+		alias = index_file_exists(istate, ce->name,
+					  ce_namelen(ce), ignore_case);
+		if (alias &&
+		    !ce_stage(alias) &&
+		    !ie_match_stat(istate, alias, st, ce_option)) {
+			/* Nothing changed, really */
+			if (!S_ISGITLINK(alias->ce_mode))
+				ce_mark_uptodate(alias);
+			alias->ce_flags |= CE_ADDED;
 
-	alias = index_file_exists(istate, ce->name, ce_namelen(ce), ignore_case);
-	if (alias && !ce_stage(alias) && !ie_match_stat(istate, alias, st, ce_option)) {
-		/* Nothing changed, really */
-		if (!S_ISGITLINK(alias->ce_mode))
-			ce_mark_uptodate(alias);
-		alias->ce_flags |= CE_ADDED;
-
-		free(ce);
-		return 0;
+			free(ce);
+			return 0;
+		}
 	}
 	if (!intent_only) {
-		if (index_path(ce->oid.hash, path, st, HASH_WRITE_OBJECT)) {
+		if (index_path(&ce->oid, path, st, newflags)) {
 			free(ce);
 			return error("unable to index file %s", path);
 		}
@@ -777,6 +796,7 @@ int chmod_index_entry(struct index_state *istate, struct cache_entry *ce,
 	}
 	cache_tree_invalidate_path(istate, ce->name);
 	ce->ce_flags |= CE_UPDATE_IN_BASE;
+	mark_fsmonitor_invalid(istate, ce);
 	istate->cache_changed |= CE_ENTRY_CHANGED;
 
 	return 0;
@@ -887,9 +907,32 @@ static int has_file_name(struct index_state *istate,
 	return retval;
 }
 
+
+/*
+ * Like strcmp(), but also return the offset of the first change.
+ * If strings are equal, return the length.
+ */
+int strcmp_offset(const char *s1, const char *s2, size_t *first_change)
+{
+	size_t k;
+
+	if (!first_change)
+		return strcmp(s1, s2);
+
+	for (k = 0; s1[k] == s2[k]; k++)
+		if (s1[k] == '\0')
+			break;
+
+	*first_change = k;
+	return (unsigned char)s1[k] - (unsigned char)s2[k];
+}
+
 /*
  * Do we have another file with a pathname that is a proper
  * subset of the name we're trying to add?
+ *
+ * That is, is there another file in the index with a path
+ * that matches a sub-directory in the given entry?
  */
 static int has_dir_name(struct index_state *istate,
 			const struct cache_entry *ce, int pos, int ok_to_replace)
@@ -898,9 +941,51 @@ static int has_dir_name(struct index_state *istate,
 	int stage = ce_stage(ce);
 	const char *name = ce->name;
 	const char *slash = name + ce_namelen(ce);
+	size_t len_eq_last;
+	int cmp_last = 0;
+
+	/*
+	 * We are frequently called during an iteration on a sorted
+	 * list of pathnames and while building a new index.  Therefore,
+	 * there is a high probability that this entry will eventually
+	 * be appended to the index, rather than inserted in the middle.
+	 * If we can confirm that, we can avoid binary searches on the
+	 * components of the pathname.
+	 *
+	 * Compare the entry's full path with the last path in the index.
+	 */
+	if (istate->cache_nr > 0) {
+		cmp_last = strcmp_offset(name,
+			istate->cache[istate->cache_nr - 1]->name,
+			&len_eq_last);
+		if (cmp_last > 0) {
+			if (len_eq_last == 0) {
+				/*
+				 * The entry sorts AFTER the last one in the
+				 * index and their paths have no common prefix,
+				 * so there cannot be a F/D conflict.
+				 */
+				return retval;
+			} else {
+				/*
+				 * The entry sorts AFTER the last one in the
+				 * index, but has a common prefix.  Fall through
+				 * to the loop below to disect the entry's path
+				 * and see where the difference is.
+				 */
+			}
+		} else if (cmp_last == 0) {
+			/*
+			 * The entry exactly matches the last one in the
+			 * index, but because of multiple stage and CE_REMOVE
+			 * items, we fall through and let the regular search
+			 * code handle it.
+			 */
+		}
+	}
 
 	for (;;) {
-		int len;
+		size_t len;
 
 		for (;;) {
 			if (*--slash == '/')
@@ -910,6 +995,67 @@ static int has_dir_name(struct index_state *istate,
 		}
 		len = slash - name;
 
+		if (cmp_last > 0) {
+			/*
+			 * (len + 1) is a directory boundary (including
+			 * the trailing slash).  And since the loop is
+			 * decrementing "slash", the first iteration is
+			 * the longest directory prefix; subsequent
+			 * iterations consider parent directories.
+			 */
+
+			if (len + 1 <= len_eq_last) {
+				/*
+				 * The directory prefix (including the trailing
+				 * slash) also appears as a prefix in the last
+				 * entry, so the remainder cannot collide (because
+				 * strcmp said the whole path was greater).
+				 *
+				 * EQ: last: xxx/A
+				 *     this: xxx/B
+				 *
+				 * LT: last: xxx/file_A
+				 *     this: xxx/file_B
+				 */
+				return retval;
+			}
+
+			if (len > len_eq_last) {
+				/*
+				 * This part of the directory prefix (excluding
+				 * the trailing slash) is longer than the known
+				 * equal portions, so this sub-directory cannot
+				 * collide with a file.
+				 *
+				 * GT: last: xxxA
+				 *     this: xxxB/file
+				 */
+				return retval;
+			}
+
+			if (istate->cache_nr > 0 &&
+				ce_namelen(istate->cache[istate->cache_nr - 1]) > len) {
+				/*
+				 * The directory prefix lines up with part of
+				 * a longer file or directory name, but sorts
+				 * after it, so this sub-directory cannot
+				 * collide with a file.
+				 *
+				 * last: xxx/yy-file (because '-' sorts before '/')
+				 * this: xxx/yy/abc
+				 */
+				return retval;
+			}
+
+			/*
+			 * This is a possible collision. Fall through and
+			 * let the regular search code handle it.
+			 *
+			 * last: xxx
+			 * this: xxx/file
+			 */
+		}
+
 		pos = index_name_stage_pos(istate, name, len, stage);
 		if (pos >= 0) {
 			/*
@@ -1001,7 +1147,16 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 
 	if (!(option & ADD_CACHE_KEEP_CACHE_TREE))
 		cache_tree_invalidate_path(istate, ce->name);
-	pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
+
+	/*
+	 * If this entry's path sorts after the last entry in the index,
+	 * we can avoid searching for it.
+	 */
+	if (istate->cache_nr > 0 &&
+		strcmp(ce->name, istate->cache[istate->cache_nr - 1]->name) > 0)
+		pos = -istate->cache_nr - 1;
+	else
+		pos = index_name_stage_pos(istate, ce->name, ce_namelen(ce), ce_stage(ce));
 
 	/* existing match? Just replace it. */
 	if (pos >= 0) {
@@ -1062,9 +1217,8 @@ int add_index_entry(struct index_state *istate, struct cache_entry *ce, int opti
 	/* Add it in.. */
 	istate->cache_nr++;
 	if (istate->cache_nr > pos + 1)
-		memmove(istate->cache + pos + 1,
-			istate->cache + pos,
-			(istate->cache_nr - pos - 1) * sizeof(ce));
+		MOVE_ARRAY(istate->cache + pos + 1, istate->cache + pos,
+			   istate->cache_nr - pos - 1);
 	set_index_entry(istate, pos, ce);
 	istate->cache_changed |= CE_ENTRY_ADDED;
 	return 0;
@@ -1093,10 +1247,13 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 	int ignore_valid = options & CE_MATCH_IGNORE_VALID;
 	int ignore_skip_worktree = options & CE_MATCH_IGNORE_SKIP_WORKTREE;
 	int ignore_missing = options & CE_MATCH_IGNORE_MISSING;
+	int ignore_fsmonitor = options & CE_MATCH_IGNORE_FSMONITOR;
 
 	if (!refresh || ce_uptodate(ce))
 		return ce;
 
+	if (!ignore_fsmonitor)
+		refresh_fsmonitor(istate);
 	/*
 	 * CE_VALID or CE_SKIP_WORKTREE means the user promised us
 	 * that the change to the work tree does not matter and told
@@ -1110,6 +1267,10 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 		ce_mark_uptodate(ce);
 		return ce;
 	}
+	if (!ignore_fsmonitor && (ce->ce_flags & CE_FSMONITOR_VALID)) {
+		ce_mark_uptodate(ce);
+		return ce;
+	}
 
 	if (has_symlink_leading_path(ce->name, ce_namelen(ce))) {
 		if (ignore_missing)
@@ -1147,8 +1308,10 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
 			 * because CE_UPTODATE flag is in-core only;
 			 * we are not going to write this change out.
 			 */
-			if (!S_ISGITLINK(ce->ce_mode))
+			if (!S_ISGITLINK(ce->ce_mode)) {
 				ce_mark_uptodate(ce);
+				mark_fsmonitor_valid(ce);
+			}
 			return ce;
 		}
 	}
@@ -1208,6 +1371,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	const char *typechange_fmt;
 	const char *added_fmt;
 	const char *unmerged_fmt;
+	uint64_t start = getnanotime();
 
 	modified_fmt = (in_porcelain ? "M\t%s\n" : "%s: needs update\n");
 	deleted_fmt = (in_porcelain ? "D\t%s\n" : "%s: needs update\n");
@@ -1215,7 +1379,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 	added_fmt = (in_porcelain ? "A\t%s\n" : "%s needs update\n");
 	unmerged_fmt = (in_porcelain ? "U\t%s\n" : "%s: needs merge\n");
 	for (i = 0; i < istate->cache_nr; i++) {
-		struct cache_entry *ce, *new;
+		struct cache_entry *ce, *new_entry;
 		int cache_errno = 0;
 		int changed = 0;
 		int filtered = 0;
@@ -1244,10 +1408,10 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 		if (filtered)
 			continue;
 
-		new = refresh_cache_ent(istate, ce, options, &cache_errno, &changed);
-		if (new == ce)
+		new_entry = refresh_cache_ent(istate, ce, options, &cache_errno, &changed);
+		if (new_entry == ce)
 			continue;
-		if (!new) {
+		if (!new_entry) {
 			const char *fmt;
 
 			if (really && cache_errno == EINVAL) {
@@ -1256,6 +1420,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 				 */
 				ce->ce_flags &= ~CE_VALID;
 				ce->ce_flags |= CE_UPDATE_IN_BASE;
+				mark_fsmonitor_invalid(istate, ce);
 				istate->cache_changed |= CE_ENTRY_CHANGED;
 			}
 			if (quiet)
@@ -1275,8 +1440,9 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 			continue;
 		}
 
-		replace_index_entry(istate, i, new);
+		replace_index_entry(istate, i, new_entry);
 	}
+	trace_performance_since(start, "refresh index");
 	return has_errors;
 }
 
@@ -1364,6 +1530,7 @@ struct ondisk_cache_entry_extended {
 };
 
 /* These are only used for v3 or lower */
+#define align_padding_size(size, len) ((size + (len) + 8) & ~7) - (size + len)
 #define align_flex_name(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
 #define ondisk_cache_entry_size(len) align_flex_name(ondisk_cache_entry,len)
 #define ondisk_cache_entry_extended_size(len) align_flex_name(ondisk_cache_entry_extended,len)
@@ -1371,10 +1538,16 @@ struct ondisk_cache_entry_extended {
 			    ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
 			    ondisk_cache_entry_size(ce_namelen(ce)))
 
+/* Allow fsck to force verification of the index checksum. */
+int verify_index_checksum;
+
+/* Allow fsck to force verification of the cache entry order. */
+int verify_ce_order;
+
 static int verify_hdr(struct cache_header *hdr, unsigned long size)
 {
-	git_SHA_CTX c;
-	unsigned char sha1[20];
+	git_hash_ctx c;
+	unsigned char hash[GIT_MAX_RAWSZ];
 	int hdr_version;
 
 	if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
@@ -1382,10 +1555,14 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)
 	hdr_version = ntohl(hdr->hdr_version);
 	if (hdr_version < INDEX_FORMAT_LB || INDEX_FORMAT_UB < hdr_version)
 		return error("bad index version %d", hdr_version);
-	git_SHA1_Init(&c);
-	git_SHA1_Update(&c, hdr, size - 20);
-	git_SHA1_Final(sha1, &c);
-	if (hashcmp(sha1, (unsigned char *)hdr + size - 20))
+
+	if (!verify_index_checksum)
+		return 0;
+
+	the_hash_algo->init_fn(&c);
+	the_hash_algo->update_fn(&c, hdr, size - the_hash_algo->rawsz);
+	the_hash_algo->final_fn(hash, &c);
+	if (hashcmp(hash, (unsigned char *)hdr + size - the_hash_algo->rawsz))
 		return error("bad index file sha1 signature");
 	return 0;
 }
@@ -1407,6 +1584,9 @@ static int read_index_extension(struct index_state *istate,
 	case CACHE_EXT_UNTRACKED:
 		istate->untracked = read_untracked_extension(data, sz);
 		break;
+	case CACHE_EXT_FSMONITOR:
+		read_fsmonitor_extension(istate, data, sz);
+		break;
 	default:
 		if (*ext < 'A' || 'Z' < *ext)
 			return error("index uses %.4s extension, which we do not understand",
@@ -1424,7 +1604,7 @@ int hold_locked_index(struct lock_file *lk, int lock_flags)
 
 int read_index(struct index_state *istate)
 {
-	return read_index_from(istate, get_index_file());
+	return read_index_from(istate, get_index_file(), get_git_dir());
 }
 
 static struct cache_entry *cache_entry_from_ondisk(struct ondisk_cache_entry *ondisk,
@@ -1524,6 +1704,9 @@ static void check_ce_order(struct index_state *istate)
 {
 	unsigned int i;
 
+	if (!verify_ce_order)
+		return;
+
 	for (i = 1; i < istate->cache_nr; i++) {
 		struct cache_entry *ce = istate->cache[i - 1];
 		struct cache_entry *next_ce = istate->cache[i];
@@ -1558,10 +1741,28 @@ static void tweak_untracked_cache(struct index_state *istate)
 	}
 }
 
+static void tweak_split_index(struct index_state *istate)
+{
+	switch (git_config_get_split_index()) {
+	case -1: /* unset: do nothing */
+		break;
+	case 0: /* false */
+		remove_split_index(istate);
+		break;
+	case 1: /* true */
+		add_split_index(istate);
+		break;
+	default: /* unknown value: do nothing */
+		break;
+	}
+}
+
 static void post_read_index_from(struct index_state *istate)
 {
 	check_ce_order(istate);
 	tweak_untracked_cache(istate);
+	tweak_split_index(istate);
+	tweak_fsmonitor(istate);
 }
 
 /* remember to discard_cache() before reading a different cache! */
@@ -1591,7 +1792,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 		die_errno("cannot stat the open index");
 
 	mmap_size = xsize_t(st.st_size);
-	if (mmap_size < sizeof(struct cache_header) + 20)
+	if (mmap_size < sizeof(struct cache_header) + the_hash_algo->rawsz)
 		die("index file smaller than expected");
 
 	mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -1603,7 +1804,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	if (verify_hdr(hdr, mmap_size) < 0)
 		goto unmap;
 
-	hashcpy(istate->sha1, (const unsigned char *)hdr + mmap_size - 20);
+	hashcpy(istate->sha1, (const unsigned char *)hdr + mmap_size - the_hash_algo->rawsz);
 	istate->version = ntohl(hdr->hdr_version);
 	istate->cache_nr = ntohl(hdr->hdr_entries);
 	istate->cache_alloc = alloc_nr(istate->cache_nr);
@@ -1631,7 +1832,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	istate->timestamp.sec = st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
 
-	while (src_offset <= mmap_size - 20 - 8) {
+	while (src_offset <= mmap_size - the_hash_algo->rawsz - 8) {
 		/* After an array of active_nr index entries,
 		 * there can be arbitrary number of extended
 		 * sections, each of which is prefixed with
@@ -1657,16 +1858,33 @@ unmap:
 	die("index file corrupt");
 }
 
-int read_index_from(struct index_state *istate, const char *path)
+/*
+ * Signal that the shared index is used by updating its mtime.
+ *
+ * This way, shared index can be removed if they have not been used
+ * for some time.
+ */
+static void freshen_shared_index(const char *shared_index, int warn)
+{
+	if (!check_and_freshen_file(shared_index, 1) && warn)
+		warning("could not freshen shared index '%s'", shared_index);
+}
+
+int read_index_from(struct index_state *istate, const char *path,
+		    const char *gitdir)
 {
+	uint64_t start = getnanotime();
 	struct split_index *split_index;
 	int ret;
+	char *base_sha1_hex;
+	char *base_path;
 
 	/* istate->initialized covers both .git/index and .git/sharedindex.xxx */
 	if (istate->initialized)
 		return istate->cache_nr;
 
 	ret = do_read_index(istate, path, 0);
+	trace_performance_since(start, "read cache %s", path);
 
 	split_index = istate->split_index;
 	if (!split_index || is_null_sha1(split_index->base_sha1)) {
@@ -1678,17 +1896,20 @@ int read_index_from(struct index_state *istate, const char *path)
 		discard_index(split_index->base);
 	else
 		split_index->base = xcalloc(1, sizeof(*split_index->base));
-	ret = do_read_index(split_index->base,
-			    git_path("sharedindex.%s",
-				     sha1_to_hex(split_index->base_sha1)), 1);
+
+	base_sha1_hex = sha1_to_hex(split_index->base_sha1);
+	base_path = xstrfmt("%s/sharedindex.%s", gitdir, base_sha1_hex);
+	ret = do_read_index(split_index->base, base_path, 1);
 	if (hashcmp(split_index->base_sha1, split_index->base->sha1))
 		die("broken index, expect %s in %s, got %s",
-		    sha1_to_hex(split_index->base_sha1),
-		    git_path("sharedindex.%s",
-			     sha1_to_hex(split_index->base_sha1)),
+		    base_sha1_hex, base_path,
 		    sha1_to_hex(split_index->base->sha1));
+
+	freshen_shared_index(base_path, 0);
 	merge_base_index(istate);
 	post_read_index_from(istate);
+	trace_performance_since(start, "read cache %s", base_path);
+	free(base_path);
 	return ret;
 }
 
@@ -1718,8 +1939,7 @@ int discard_index(struct index_state *istate)
 	free_name_hash(istate);
 	cache_tree_free(&(istate->cache_tree));
 	istate->initialized = 0;
-	free(istate->cache);
-	istate->cache = NULL;
+	FREE_AND_NULL(istate->cache);
 	istate->cache_alloc = 0;
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
@@ -1741,19 +1961,19 @@ int unmerged_index(const struct index_state *istate)
 static unsigned char write_buffer[WRITE_BUFFER_SIZE];
 static unsigned long write_buffer_len;
 
-static int ce_write_flush(git_SHA_CTX *context, int fd)
+static int ce_write_flush(git_hash_ctx *context, int fd)
 {
 	unsigned int buffered = write_buffer_len;
 	if (buffered) {
-		git_SHA1_Update(context, write_buffer, buffered);
-		if (write_in_full(fd, write_buffer, buffered) != buffered)
+		the_hash_algo->update_fn(context, write_buffer, buffered);
+		if (write_in_full(fd, write_buffer, buffered) < 0)
 			return -1;
 		write_buffer_len = 0;
 	}
 	return 0;
 }
 
-static int ce_write(git_SHA_CTX *context, int fd, void *data, unsigned int len)
+static int ce_write(git_hash_ctx *context, int fd, void *data, unsigned int len)
 {
 	while (len) {
 		unsigned int buffered = write_buffer_len;
@@ -1775,7 +1995,7 @@ static int ce_write(git_SHA_CTX *context, int fd, void *data, unsigned int len)
 	return 0;
 }
 
-static int write_index_ext_header(git_SHA_CTX *context, int fd,
+static int write_index_ext_header(git_hash_ctx *context, int fd,
 				  unsigned int ext, unsigned int sz)
 {
 	ext = htonl(ext);
@@ -1784,27 +2004,27 @@ static int write_index_ext_header(git_SHA_CTX *context, int fd,
 		(ce_write(context, fd, &sz, 4) < 0)) ? -1 : 0;
 }
 
-static int ce_flush(git_SHA_CTX *context, int fd, unsigned char *sha1)
+static int ce_flush(git_hash_ctx *context, int fd, unsigned char *hash)
 {
 	unsigned int left = write_buffer_len;
 
 	if (left) {
 		write_buffer_len = 0;
-		git_SHA1_Update(context, write_buffer, left);
+		the_hash_algo->update_fn(context, write_buffer, left);
 	}
 
-	/* Flush first if not enough space for SHA1 signature */
-	if (left + 20 > WRITE_BUFFER_SIZE) {
-		if (write_in_full(fd, write_buffer, left) != left)
+	/* Flush first if not enough space for hash signature */
+	if (left + the_hash_algo->rawsz > WRITE_BUFFER_SIZE) {
+		if (write_in_full(fd, write_buffer, left) < 0)
 			return -1;
 		left = 0;
 	}
 
-	/* Append the SHA1 signature at the end */
-	git_SHA1_Final(write_buffer + left, context);
-	hashcpy(sha1, write_buffer + left);
-	left += 20;
-	return (write_in_full(fd, write_buffer, left) != left) ? -1 : 0;
+	/* Append the hash signature at the end */
+	the_hash_algo->final_fn(write_buffer + left, context);
+	hashcpy(hash, write_buffer + left);
+	left += the_hash_algo->rawsz;
+	return (write_in_full(fd, write_buffer, left) < 0) ? -1 : 0;
 }
 
 static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
@@ -1857,7 +2077,7 @@ static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
 }
 
 /* Copy miscellaneous fields but not the name */
-static char *copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
+static void copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
 				       struct cache_entry *ce)
 {
 	short flags;
@@ -1881,32 +2101,35 @@ static char *copy_cache_entry_to_ondisk(struct ondisk_cache_entry *ondisk,
 		struct ondisk_cache_entry_extended *ondisk2;
 		ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
 		ondisk2->flags2 = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
-		return ondisk2->name;
-	}
-	else {
-		return ondisk->name;
 	}
 }
 
-static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce,
-			  struct strbuf *previous_name)
+static int ce_write_entry(git_hash_ctx *c, int fd, struct cache_entry *ce,
+			  struct strbuf *previous_name, struct ondisk_cache_entry *ondisk)
 {
 	int size;
-	struct ondisk_cache_entry *ondisk;
 	int saved_namelen = saved_namelen; /* compiler workaround */
-	char *name;
 	int result;
+	static unsigned char padding[8] = { 0x00 };
 
 	if (ce->ce_flags & CE_STRIP_NAME) {
 		saved_namelen = ce_namelen(ce);
 		ce->ce_namelen = 0;
 	}
 
+	if (ce->ce_flags & CE_EXTENDED)
+		size = offsetof(struct ondisk_cache_entry_extended, name);
+	else
+		size = offsetof(struct ondisk_cache_entry, name);
+
 	if (!previous_name) {
-		size = ondisk_ce_size(ce);
-		ondisk = xcalloc(1, size);
-		name = copy_cache_entry_to_ondisk(ondisk, ce);
-		memcpy(name, ce->name, ce_namelen(ce));
+		int len = ce_namelen(ce);
+		copy_cache_entry_to_ondisk(ondisk, ce);
+		result = ce_write(c, fd, ondisk, size);
+		if (!result)
+			result = ce_write(c, fd, ce->name, len);
+		if (!result)
+			result = ce_write(c, fd, padding, align_padding_size(size, len));
 	} else {
 		int common, to_remove, prefix_size;
 		unsigned char to_remove_vi[16];
@@ -1919,16 +2142,14 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce,
 		to_remove = previous_name->len - common;
 		prefix_size = encode_varint(to_remove, to_remove_vi);
 
-		if (ce->ce_flags & CE_EXTENDED)
-			size = offsetof(struct ondisk_cache_entry_extended, name);
-		else
-			size = offsetof(struct ondisk_cache_entry, name);
-		size += prefix_size + (ce_namelen(ce) - common + 1);
-
-		ondisk = xcalloc(1, size);
-		name = copy_cache_entry_to_ondisk(ondisk, ce);
-		memcpy(name, to_remove_vi, prefix_size);
-		memcpy(name + prefix_size, ce->name + common, ce_namelen(ce) - common);
+		copy_cache_entry_to_ondisk(ondisk, ce);
+		result = ce_write(c, fd, ondisk, size);
+		if (!result)
+			result = ce_write(c, fd, to_remove_vi, prefix_size);
+		if (!result)
+			result = ce_write(c, fd, ce->name + common, ce_namelen(ce) - common);
+		if (!result)
+			result = ce_write(c, fd, padding, 1);
 
 		strbuf_splice(previous_name, common, to_remove,
 			      ce->name + common, ce_namelen(ce) - common);
@@ -1938,8 +2159,6 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce,
 		ce->ce_flags &= ~CE_STRIP_NAME;
 	}
 
-	result = ce_write(c, fd, ondisk, size);
-	free(ondisk);
 	return result;
 }
 
@@ -1952,7 +2171,7 @@ static int verify_index_from(const struct index_state *istate, const char *path)
 	int fd;
 	ssize_t n;
 	struct stat st;
-	unsigned char sha1[20];
+	unsigned char hash[GIT_MAX_RAWSZ];
 
 	if (!istate->initialized)
 		return 0;
@@ -1964,14 +2183,14 @@ static int verify_index_from(const struct index_state *istate, const char *path)
 	if (fstat(fd, &st))
 		goto out;
 
-	if (st.st_size < sizeof(struct cache_header) + 20)
+	if (st.st_size < sizeof(struct cache_header) + the_hash_algo->rawsz)
 		goto out;
 
-	n = pread_in_full(fd, sha1, 20, st.st_size - 20);
-	if (n != 20)
+	n = pread_in_full(fd, hash, the_hash_algo->rawsz, st.st_size - the_hash_algo->rawsz);
+	if (n != the_hash_algo->rawsz)
 		goto out;
 
-	if (hashcmp(istate->sha1, sha1))
+	if (hashcmp(istate->sha1, hash))
 		goto out;
 
 	close(fd);
@@ -2000,27 +2219,36 @@ static int has_racy_timestamp(struct index_state *istate)
 	return 0;
 }
 
-/*
- * Opportunistically update the index but do not complain if we can't
- */
 void update_index_if_able(struct index_state *istate, struct lock_file *lockfile)
 {
 	if ((istate->cache_changed || has_racy_timestamp(istate)) &&
-	    verify_index(istate) &&
-	    write_locked_index(istate, lockfile, COMMIT_LOCK))
+	    verify_index(istate))
+		write_locked_index(istate, lockfile, COMMIT_LOCK);
+	else
 		rollback_lock_file(lockfile);
 }
 
-static int do_write_index(struct index_state *istate, int newfd,
+/*
+ * On success, `tempfile` is closed. If it is the temporary file
+ * of a `struct lock_file`, we will therefore effectively perform
+ * a 'close_lock_file_gently()`. Since that is an implementation
+ * detail of lockfiles, callers of `do_write_index()` should not
+ * rely on it.
+ */
+static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
 			  int strip_extensions)
 {
-	git_SHA_CTX c;
+	uint64_t start = getnanotime();
+	int newfd = tempfile->fd;
+	git_hash_ctx c;
 	struct cache_header hdr;
-	int i, err, removed, extended, hdr_version;
+	int i, err = 0, removed, extended, hdr_version;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
 	struct stat st;
+	struct ondisk_cache_entry_extended ondisk;
 	struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
+	int drop_cache_tree = istate->drop_cache_tree;
 
 	for (i = removed = extended = 0; i < entries; i++) {
 		if (cache[i]->ce_flags & CE_REMOVE)
@@ -2050,11 +2278,12 @@ static int do_write_index(struct index_state *istate, int newfd,
 	hdr.hdr_version = htonl(hdr_version);
 	hdr.hdr_entries = htonl(entries - removed);
 
-	git_SHA1_Init(&c);
+	the_hash_algo->init_fn(&c);
 	if (ce_write(&c, newfd, &hdr, sizeof(hdr)) < 0)
 		return -1;
 
 	previous_name = (hdr_version == 4) ? &previous_name_buf : NULL;
+
 	for (i = 0; i < entries; i++) {
 		struct cache_entry *ce = cache[i];
 		if (ce->ce_flags & CE_REMOVE)
@@ -2070,13 +2299,21 @@ static int do_write_index(struct index_state *istate, int newfd,
 			if (allow)
 				warning(msg, ce->name);
 			else
-				return error(msg, ce->name);
+				err = error(msg, ce->name);
+
+			drop_cache_tree = 1;
 		}
-		if (ce_write_entry(&c, newfd, ce, previous_name) < 0)
-			return -1;
+		if (ce_write_entry(&c, newfd, ce, previous_name, (struct ondisk_cache_entry *)&ondisk) < 0)
+			err = -1;
+
+		if (err)
+			break;
 	}
 	strbuf_release(&previous_name_buf);
 
+	if (err)
+		return err;
+
 	/* Write extension data here */
 	if (!strip_extensions && istate->split_index) {
 		struct strbuf sb = STRBUF_INIT;
@@ -2089,7 +2326,7 @@ static int do_write_index(struct index_state *istate, int newfd,
 		if (err)
 			return -1;
 	}
-	if (!strip_extensions && istate->cache_tree) {
+	if (!strip_extensions && !drop_cache_tree && istate->cache_tree) {
 		struct strbuf sb = STRBUF_INIT;
 
 		cache_tree_write(&sb, istate->cache_tree);
@@ -2121,11 +2358,28 @@ static int do_write_index(struct index_state *istate, int newfd,
 		if (err)
 			return -1;
 	}
+	if (!strip_extensions && istate->fsmonitor_last_update) {
+		struct strbuf sb = STRBUF_INIT;
+
+		write_fsmonitor_extension(&sb, istate);
+		err = write_index_ext_header(&c, newfd, CACHE_EXT_FSMONITOR, sb.len) < 0
+			|| ce_write(&c, newfd, sb.buf, sb.len) < 0;
+		strbuf_release(&sb);
+		if (err)
+			return -1;
+	}
 
-	if (ce_flush(&c, newfd, istate->sha1) || fstat(newfd, &st))
+	if (ce_flush(&c, newfd, istate->sha1))
+		return -1;
+	if (close_tempfile_gently(tempfile)) {
+		error(_("could not close '%s'"), tempfile->filename.buf);
+		return -1;
+	}
+	if (stat(tempfile->filename.buf, &st))
 		return -1;
 	istate->timestamp.sec = (unsigned int)st.st_mtime;
 	istate->timestamp.nsec = ST_MTIME_NSEC(st);
+	trace_performance_since(start, "write index, changed mask = %x", istate->cache_changed);
 	return 0;
 }
 
@@ -2145,17 +2399,12 @@ static int commit_locked_index(struct lock_file *lk)
 static int do_write_locked_index(struct index_state *istate, struct lock_file *lock,
 				 unsigned flags)
 {
-	int ret = do_write_index(istate, get_lock_file_fd(lock), 0);
+	int ret = do_write_index(istate, lock->tempfile, 0);
 	if (ret)
 		return ret;
-	assert((flags & (COMMIT_LOCK | CLOSE_LOCK)) !=
-	       (COMMIT_LOCK | CLOSE_LOCK));
 	if (flags & COMMIT_LOCK)
 		return commit_locked_index(lock);
-	else if (flags & CLOSE_LOCK)
-		return close_lock_file(lock);
-	else
-		return ret;
+	return close_lock_file_gently(lock);
 }
 
 static int write_split_index(struct index_state *istate,
@@ -2169,42 +2418,135 @@ static int write_split_index(struct index_state *istate,
 	return ret;
 }
 
-static struct tempfile temporary_sharedindex;
+static const char *shared_index_expire = "2.weeks.ago";
+
+static unsigned long get_shared_index_expire_date(void)
+{
+	static unsigned long shared_index_expire_date;
+	static int shared_index_expire_date_prepared;
+
+	if (!shared_index_expire_date_prepared) {
+		git_config_get_expiry("splitindex.sharedindexexpire",
+				      &shared_index_expire);
+		shared_index_expire_date = approxidate(shared_index_expire);
+		shared_index_expire_date_prepared = 1;
+	}
+
+	return shared_index_expire_date;
+}
+
+static int should_delete_shared_index(const char *shared_index_path)
+{
+	struct stat st;
+	unsigned long expiration;
+
+	/* Check timestamp */
+	expiration = get_shared_index_expire_date();
+	if (!expiration)
+		return 0;
+	if (stat(shared_index_path, &st))
+		return error_errno(_("could not stat '%s'"), shared_index_path);
+	if (st.st_mtime > expiration)
+		return 0;
+
+	return 1;
+}
+
+static int clean_shared_index_files(const char *current_hex)
+{
+	struct dirent *de;
+	DIR *dir = opendir(get_git_dir());
+
+	if (!dir)
+		return error_errno(_("unable to open git dir: %s"), get_git_dir());
+
+	while ((de = readdir(dir)) != NULL) {
+		const char *sha1_hex;
+		const char *shared_index_path;
+		if (!skip_prefix(de->d_name, "sharedindex.", &sha1_hex))
+			continue;
+		if (!strcmp(sha1_hex, current_hex))
+			continue;
+		shared_index_path = git_path("%s", de->d_name);
+		if (should_delete_shared_index(shared_index_path) > 0 &&
+		    unlink(shared_index_path))
+			warning_errno(_("unable to unlink: %s"), shared_index_path);
+	}
+	closedir(dir);
+
+	return 0;
+}
 
 static int write_shared_index(struct index_state *istate,
-			      struct lock_file *lock, unsigned flags)
+			      struct tempfile **temp)
 {
 	struct split_index *si = istate->split_index;
-	int fd, ret;
+	int ret;
 
-	fd = mks_tempfile(&temporary_sharedindex, git_path("sharedindex_XXXXXX"));
-	if (fd < 0) {
-		hashclr(si->base_sha1);
-		return do_write_locked_index(istate, lock, flags);
-	}
 	move_cache_to_base_index(istate);
-	ret = do_write_index(si->base, fd, 1);
+	ret = do_write_index(si->base, *temp, 1);
+	if (ret)
+		return ret;
+	ret = adjust_shared_perm(get_tempfile_path(*temp));
 	if (ret) {
-		delete_tempfile(&temporary_sharedindex);
+		error("cannot fix permission bits on %s", get_tempfile_path(*temp));
 		return ret;
 	}
-	ret = rename_tempfile(&temporary_sharedindex,
+	ret = rename_tempfile(temp,
 			      git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
-	if (!ret)
+	if (!ret) {
 		hashcpy(si->base_sha1, si->base->sha1);
+		clean_shared_index_files(sha1_to_hex(si->base->sha1));
+	}
+
 	return ret;
 }
 
+static const int default_max_percent_split_change = 20;
+
+static int too_many_not_shared_entries(struct index_state *istate)
+{
+	int i, not_shared = 0;
+	int max_split = git_config_get_max_percent_split_change();
+
+	switch (max_split) {
+	case -1:
+		/* not or badly configured: use the default value */
+		max_split = default_max_percent_split_change;
+		break;
+	case 0:
+		return 1; /* 0% means always write a new shared index */
+	case 100:
+		return 0; /* 100% means never write a new shared index */
+	default:
+		break; /* just use the configured value */
+	}
+
+	/* Count not shared entries */
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		if (!ce->index)
+			not_shared++;
+	}
+
+	return (int64_t)istate->cache_nr * max_split < (int64_t)not_shared * 100;
+}
+
 int write_locked_index(struct index_state *istate, struct lock_file *lock,
 		       unsigned flags)
 {
+	int new_shared_index, ret;
 	struct split_index *si = istate->split_index;
 
+	if (istate->fsmonitor_last_update)
+		fill_fsmonitor_bitmap(istate);
+
 	if (!si || alternate_index_output ||
 	    (istate->cache_changed & ~EXTMASK)) {
 		if (si)
 			hashclr(si->base_sha1);
-		return do_write_locked_index(istate, lock, flags);
+		ret = do_write_locked_index(istate, lock, flags);
+		goto out;
 	}
 
 	if (getenv("GIT_TEST_SPLIT_INDEX")) {
@@ -2212,13 +2554,45 @@ int write_locked_index(struct index_state *istate, struct lock_file *lock,
 		if ((v & 15) < 6)
 			istate->cache_changed |= SPLIT_INDEX_ORDERED;
 	}
-	if (istate->cache_changed & SPLIT_INDEX_ORDERED) {
-		int ret = write_shared_index(istate, lock, flags);
+	if (too_many_not_shared_entries(istate))
+		istate->cache_changed |= SPLIT_INDEX_ORDERED;
+
+	new_shared_index = istate->cache_changed & SPLIT_INDEX_ORDERED;
+
+	if (new_shared_index) {
+		struct tempfile *temp;
+		int saved_errno;
+
+		temp = mks_tempfile(git_path("sharedindex_XXXXXX"));
+		if (!temp) {
+			hashclr(si->base_sha1);
+			ret = do_write_locked_index(istate, lock, flags);
+			goto out;
+		}
+		ret = write_shared_index(istate, &temp);
+
+		saved_errno = errno;
+		if (is_tempfile_active(temp))
+			delete_tempfile(&temp);
+		errno = saved_errno;
+
 		if (ret)
-			return ret;
+			goto out;
+	}
+
+	ret = write_split_index(istate, lock, flags);
+
+	/* Freshen the shared index only if the split-index was written */
+	if (!ret && !new_shared_index) {
+		const char *shared_index = git_path("sharedindex.%s",
+						    sha1_to_hex(si->base_sha1));
+		freshen_shared_index(shared_index, 1);
 	}
 
-	return write_split_index(istate, lock, flags);
+out:
+	if (flags & COMMIT_LOCK)
+		rollback_lock_file(lock);
+	return ret;
 }
 
 /*
@@ -2321,8 +2695,7 @@ void *read_blob_data_from_index(const struct index_state *istate,
 
 void stat_validity_clear(struct stat_validity *sv)
 {
-	free(sv->sd);
-	sv->sd = NULL;
+	FREE_AND_NULL(sv->sd);
 }
 
 int stat_validity_check(struct stat_validity *sv, const char *path)
@@ -2348,3 +2721,9 @@ void stat_validity_update(struct stat_validity *sv, int fd)
 		fill_stat_data(sv->sd, &st);
 	}
 }
+
+void move_index_extensions(struct index_state *dst, struct index_state *src)
+{
+	dst->untracked = src->untracked;
+	src->untracked = NULL;
+}