[PATCH v6 00/19] index-helper/watchman

@@ -1345,7 +1345,7 @@ struct ondisk_cache_entry_extended {
 			    ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
 			    ondisk_cache_entry_size(ce_namelen(ce)))
 
-static int verify_hdr(struct cache_header *hdr, unsigned long size)
+static int verify_hdr(const struct cache_header *hdr, unsigned long size)
 {
 	git_SHA_CTX c;
 	unsigned char sha1[20];

@@ -71,6 +71,7 @@
 /git-http-fetch
 /git-http-push
 /git-imap-send
+/git-index-helper
 /git-index-pack
 /git-init
 /git-init-db

@@ -0,0 +1,47 @@
+git-index-helper(1)
+===================
+
+NAME
+----
+git-index-helper - A simple cache daemon for speeding up index file access
+
+SYNOPSIS
+--------
+[verse]
+'git index-helper' [options]
+
+DESCRIPTION
+-----------
+Keep the index file in memory for faster access. This daemon is per
+repository.
+
+OPTIONS
+-------
+
+--exit-after=<n>::
+	Exit if the cached index is not accessed for `<n>`
+	seconds. Specify 0 to wait forever. Default is 600.
+
+NOTES
+-----
+
+$GIT_DIR/index-helper.sock a Unix domain socket that the daemon reads
+commands from.  The directory will also contain files named
+"shm-index-<SHA1>".  These are used as backing stores for shared
+memory.  Normally the daemon will clean up these files when it exits
+or when they are no longer relevant.  But if it crashes, some objects
+could remain there and they can be safely deleted with "rm"
+command. The following commands are used to control the daemon:
+
+"refresh"::
+	Reread the index.
+
+"poke":
+	Let the daemon know the index is to be read. It keeps the
+	daemon alive longer, unless `--exit-after=0` is used.
+
+All commands and replies are terminated by a 0 byte.
+
+GIT
+---
+Part of the linkgit:git[1] suite

@@ -1433,6 +1433,10 @@ ifdef HAVE_DEV_TTY
 	BASIC_CFLAGS += -DHAVE_DEV_TTY
 endif
 
+ifndef NO_MMAP
+	PROGRAM_OBJS += index-helper.o
+endif
+
 ifdef DIR_HAS_BSD_GROUP_SEMANTICS
 	COMPAT_CFLAGS += -DDIR_HAS_BSD_GROUP_SEMANTICS
 endif

@@ -2159,6 +2163,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
 	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
+	@echo NO_MMAP=\''$(subst ','\'',$(subst ','\'',$(NO_MMAP)))'\' >>$@+
 ifdef TEST_OUTPUT_DIRECTORY
 	@echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@+
 endif

@@ -334,6 +334,8 @@ struct index_state {
 	struct cache_time timestamp;
 	unsigned name_hash_initialized : 1,
 		 keep_mmap : 1,
+		 from_shm : 1,
+		 to_shm : 1,
 		 initialized : 1;
 	struct hashmap name_hash;
 	struct hashmap dir_hash;

@@ -513,6 +513,7 @@ static inline int ends_with(const char *str, const char *suffix)
 #define PROT_READ 1
 #define PROT_WRITE 2
 #define MAP_PRIVATE 1
+#define MAP_SHARED 2
 #endif
 
 #define mmap git_mmap

@@ -0,0 +1,285 @@
+#include "cache.h"
+#include "parse-options.h"
+#include "sigchain.h"
+#include "strbuf.h"
+#include "exec_cmd.h"
+#include "split-index.h"
+#include "lockfile.h"
+#include "cache.h"
+#include "unix-socket.h"
+#include "pkt-line.h"
+
+struct shm {
+	unsigned char sha1[20];
+	void *shm;
+	size_t size;
+};
+
+static struct shm shm_index;
+static struct shm shm_base_index;
+
+static void release_index_shm(struct shm *is)
+{
+	if (!is->shm)
+		return;
+	munmap(is->shm, is->size);
+	unlink(git_path("shm-index-%s", sha1_to_hex(is->sha1)));
+	is->shm = NULL;
+}
+
+static void cleanup_shm(void)
+{
+	release_index_shm(&shm_index);
+	release_index_shm(&shm_base_index);
+}
+
+static void cleanup(void)
+{
+	unlink(git_path("index-helper.sock"));
+	cleanup_shm();
+}
+
+static void cleanup_on_signal(int sig)
+{
+	/* We ignore sigpipes -- that's just a client being broken. */
+	if (sig == SIGPIPE)
+		return;
+	cleanup();
+	sigchain_pop(sig);
+	raise(sig);
+}
+
+static int shared_mmap_create(int file_flags, int file_mode, size_t size,
+			      void **new_mmap, int mmap_prot, int mmap_flags,
+			      const char *path)
+{
+	int fd = -1;
+	int ret = -1;
+
+	fd = open(path, file_flags, file_mode);
+
+	if (fd < 0)
+		goto done;
+
+	if (ftruncate(fd, size))
+		goto done;
+
+	*new_mmap = mmap(NULL, size, mmap_prot, mmap_flags, fd, 0);
+
+	if (*new_mmap == MAP_FAILED) {
+		*new_mmap = NULL;
+		goto done;
+	}
+	madvise(new_mmap, size, MADV_WILLNEED);
+
+	ret = 0;
+done:
+	if (fd > 0)
+		close(fd);
+	return ret;
+}
+
+static void share_index(struct index_state *istate, struct shm *is)
+{
+	void *new_mmap;
+	if (istate->mmap_size <= 20 ||
+	    hashcmp(istate->sha1,
+		    (unsigned char *)istate->mmap + istate->mmap_size - 20) ||
+	    !hashcmp(istate->sha1, is->sha1) ||
+	    shared_mmap_create(O_CREAT | O_EXCL | O_RDWR, 0700,
+			       istate->mmap_size, &new_mmap,
+			       PROT_READ | PROT_WRITE, MAP_SHARED,
+			       git_path("shm-index-%s",
+					sha1_to_hex(istate->sha1))) < 0)
+		return;
+
+	release_index_shm(is);
+	is->size = istate->mmap_size;
+	is->shm = new_mmap;
+	hashcpy(is->sha1, istate->sha1);
+
+	memcpy(new_mmap, istate->mmap, istate->mmap_size - 20);
+
+	/*
+	 * The trailing hash must be written last after everything is
+	 * written. It's the indication that the shared memory is now
+	 * ready.
+	 * The memory barrier here matches read-cache.c:try_shm.
+	 */
+	__sync_synchronize();
+
+	hashcpy((unsigned char *)new_mmap + istate->mmap_size - 20, is->sha1);
+}
+
+static void share_the_index(void)
+{
+	if (the_index.split_index && the_index.split_index->base)
+		share_index(the_index.split_index->base, &shm_base_index);
+	share_index(&the_index, &shm_index);
+	discard_index(&the_index);
+}
+
+static void set_socket_blocking_flag(int fd, int make_nonblocking)
+{
+	int flags;
+
+	flags = fcntl(fd, F_GETFL, NULL);
+
+	if (flags < 0)
+		die(_("fcntl failed"));
+
+	if (make_nonblocking)
+		flags |= O_NONBLOCK;
+	else
+		flags &= ~O_NONBLOCK;
+
+	if (fcntl(fd, F_SETFL, flags) < 0)
+		die(_("fcntl failed"));
+}
+
+static void refresh(void)
+{
+	discard_index(&the_index);
+	the_index.keep_mmap = 1;
+	the_index.to_shm    = 1;
+	if (read_cache() < 0)
+		die(_("could not read index"));
+	share_the_index();
+}
+
+#ifndef NO_MMAP
+
+static void loop(int fd, int idle_in_seconds)
+{
+	struct timeval timeout;
+	struct timeval *timeout_p;
+
+	while (1) {
+		fd_set readfds;
+		int result, client_fd;
+		int flags;
+		char buf[4096];
+		int bytes_read;
+
+		/* need to reset timer in case select() decremented it */
+		if (idle_in_seconds) {
+			timeout.tv_usec = 0;
+			timeout.tv_sec = idle_in_seconds;
+			timeout_p = &timeout;
+		} else {
+			timeout_p = NULL;
+		}
+
+		/* Wait for a request */
+		FD_ZERO(&readfds);
+		FD_SET(fd, &readfds);
+		result = select(fd + 1, &readfds, NULL, NULL, timeout_p);
+		if (result < 0) {
+			if (errno == EINTR)
+				/*
+				 * This can lead to an overlong keepalive,
+				 * but that is better than a premature exit.
+				 */
+				continue;
+			die_errno(_("select() failed"));
+		}
+		if (result == 0)
+			/* timeout */
+			break;
+
+		client_fd = accept(fd, NULL, NULL);
+		if (client_fd < 0)
+			/*
+			 * An error here is unlikely -- it probably
+			 * indicates that the connecting process has
+			 * already dropped the connection.
+			 */
+			continue;
+
+		/*
+		 * Our connection to the client is blocking since a client
+		 * can always be killed by SIGINT or similar.
+		 */
+		set_socket_blocking_flag(client_fd, 0);
+
+		flags = PACKET_READ_GENTLE_ON_EOF | PACKET_READ_CHOMP_NEWLINE;
+		bytes_read = packet_read(client_fd, NULL, NULL, buf,
+					 sizeof(buf), flags);
+
+		if (bytes_read > 0) {
+			/* ensure string termination */
+			buf[bytes_read] = 0;
+			if (!strcmp(buf, "refresh")) {
+				refresh();
+			} else if (!strcmp(buf, "poke")) {
+				/*
+				 * Just a poke to keep us
+				 * alive, nothing to do.
+				 */
+			} else {
+				warning("BUG: Bogus command %s", buf);
+			}
+		} else {
+			/*
+			 * No command from client.  Probably it's just
+			 * a liveness check or client error.  Just
+			 * close up.
+			 */
+		}
+		close(client_fd);
+	}
+
+	close(fd);
+}
+
+#else
+
+static void loop(int fd, int idle_in_seconds)
+{
+	die(_("index-helper is not supported on this platform"));
+}
+
+#endif
+
+static const char * const usage_text[] = {
+	N_("git index-helper [options]"),
+	NULL
+};
+
+int main(int argc, char **argv)
+{
+	const char *prefix;
+	int idle_in_seconds = 600;
+	int fd;
+	struct strbuf socket_path = STRBUF_INIT;
+	struct option options[] = {
+		OPT_INTEGER(0, "exit-after", &idle_in_seconds,
+			    N_("exit if not used after some seconds")),
+		OPT_END()
+	};
+
+	git_extract_argv0_path(argv[0]);
+	git_setup_gettext();
+
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage_with_options(usage_text, options);
+
+	prefix = setup_git_directory();
+	if (parse_options(argc, (const char **)argv, prefix,
+			  options, usage_text, 0))
+		die(_("too many arguments"));
+
+	atexit(cleanup);
+	sigchain_push_common(cleanup_on_signal);
+
+	strbuf_git_path(&socket_path, "index-helper.sock");
+
+	fd = unix_stream_listen(socket_path.buf);
+	if (fd < 0)
+		die_errno(_("could not set up index-helper socket"));
+
+	loop(fd, idle_in_seconds);
+
+	close(fd);
+	return 0;
+}

@@ -18,6 +18,8 @@
 #include "varint.h"
 #include "split-index.h"
 #include "utf8.h"
+#include "unix-socket.h"
+#include "pkt-line.h"
 
 static struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
 					       unsigned int options);

@@ -1541,6 +1543,96 @@ static void post_read_index_from(struct index_state *istate)
 	tweak_untracked_cache(istate);
 }
 
+static int poke_daemon(struct index_state *istate,
+		       const struct stat *st, int refresh_cache)
+{
+	int fd;
+	int ret = 0;
+	const char *socket_path;
+
+	/* if this is from index-helper, do not poke itself (recursively) */
+	if (istate->to_shm)
+		return 0;
+
+	socket_path = git_path("index-helper.sock");
+	if (!socket_path)
+		return -1;
+
+	fd = unix_stream_connect(socket_path);
+	if (refresh_cache) {
+		packet_write(fd, "refresh");
+	} else {
+		packet_write(fd, "poke");
+	}
+	packet_flush(fd);
+
+	close(fd);
+	return ret;
+}
+
+static int is_main_index(struct index_state *istate)
+{
+	return istate == &the_index ||
+		(the_index.split_index &&
+		 istate == the_index.split_index->base);
+}
+
+/*
+ * Try to open and verify a cached shm index if available. Return 0 if
+ * succeeds (istate->mmap and istate->mmap_size are updated). Return
+ * negative otherwise.
+ */
+static int try_shm(struct index_state *istate)
+{
+	void *new_mmap = NULL;
+	size_t old_size = istate->mmap_size;
+	ssize_t new_size;
+	const unsigned char *sha1;
+	struct stat st;
+	int fd = -1;
+
+	if (!is_main_index(istate) ||
+	    old_size <= 20 ||
+	    stat(git_path("index-helper.sock"), &st))
+		return -1;
+	if (poke_daemon(istate, &st, 0))
+		return -1;
+	sha1 = (unsigned char *)istate->mmap + old_size - 20;
+
+	fd = open(git_path("shm-index-%s", sha1_to_hex(sha1)), O_RDONLY);
+	if (fd < 0)
+		goto fail;
+
+	if (fstat(fd, &st))
+		goto fail;
+
+	new_size = st.st_size;
+	new_mmap = mmap(NULL, new_size, PROT_READ, MAP_SHARED, fd, 0);
+	if (new_size <= 20 ||
+	    hashcmp((unsigned char *)istate->mmap + old_size - 20,
+		    (unsigned char *)new_mmap + new_size - 20)) {
+		if (new_mmap)
+			munmap(new_mmap, new_size);
+		goto fail;
+	}
+
+	/* The memory barrier here matches index-helper.c:share_index. */
+	__sync_synchronize();
+
+	munmap(istate->mmap, istate->mmap_size);
+	istate->mmap = new_mmap;
+	istate->mmap_size = new_size;
+	istate->from_shm = 1;
+	close(fd);
+	return 0;
+
+fail:
+	if (fd >= 0)
+		close(fd);
+	poke_daemon(istate, &st, 1);
+	return -1;
+}
+
 /* remember to discard_cache() before reading a different cache! */
 int do_read_index(struct index_state *istate, const char *path, int must_exist)
 {

@@ -1555,6 +1647,7 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	istate->from_shm = 0;
 	istate->timestamp.sec = 0;
 	istate->timestamp.nsec = 0;
 	fd = open(path, O_RDONLY);

@@ -1574,15 +1667,17 @@ int do_read_index(struct index_state *istate, const char *path, int must_exist)
 	mmap = xmmap(NULL, mmap_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	if (mmap == MAP_FAILED)
 		die_errno("unable to map index file");
-	if (istate->keep_mmap) {
-		istate->mmap = mmap;
-		istate->mmap_size = mmap_size;
-	}
 	close(fd);
 
-	hdr = mmap;
-	if (verify_hdr(hdr, mmap_size) < 0)
+	istate->mmap = mmap;
+	istate->mmap_size = mmap_size;
+	if (try_shm(istate) &&
+	    verify_hdr(istate->mmap, istate->mmap_size) < 0)
 		goto unmap;
+	hdr = mmap = istate->mmap;
+	mmap_size = istate->mmap_size;
+	if (!istate->keep_mmap)
+		istate->mmap = NULL;
 
 	hashcpy(istate->sha1, (const unsigned char *)hdr + mmap_size - 20);
 	istate->version = ntohl(hdr->hdr_version);

@@ -1662,6 +1757,8 @@ int read_index_from(struct index_state *istate, const char *path)
 	else
 		split_index->base = xcalloc(1, sizeof(*split_index->base));
 	split_index->base->keep_mmap = istate->keep_mmap;
+	split_index->base->to_shm    = istate->to_shm;
+	split_index->base->from_shm  = istate->from_shm;
 	ret = do_read_index(split_index->base,
 			    git_path("sharedindex.%s",
 				     sha1_to_hex(split_index->base_sha1)), 1);

@@ -1712,6 +1809,8 @@ int discard_index(struct index_state *istate)
 	discard_split_index(istate);
 	free_untracked_cache(istate->untracked);
 	istate->untracked = NULL;
+	istate->from_shm = 0;
+	istate->to_shm   = 0;
 	return 0;
 }
 

@@ -2138,9 +2237,14 @@ static int do_write_locked_index(struct index_state *istate, struct lock_file *l
 		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)
+	if (flags & COMMIT_LOCK) {
+		struct stat st;
+		ret = commit_locked_index(lock);
+		if (!ret && is_main_index(istate) &&
+		    !stat(git_path("index-helper.sock"), &st))
+			poke_daemon(istate, &st, 1);
+		return ret;
+	} else if (flags & CLOSE_LOCK)
 		return close_lock_file(lock);
 	else
 		return ret;

@@ -0,0 +1,23 @@
+#!/bin/sh
+#
+# Copyright (c) 2016, Twitter, Inc
+#
+
+test_description='git-index-helper
+
+Testing git index-helper
+'
+
+. ./test-lib.sh
+
+test -n "$NO_MMAP" && {
+	skip_all='skipping index-helper tests: no mmap'
+	test_done
+}
+
+test_expect_success 'index-helper smoke test' '
+	git index-helper --exit-after 1 &&
+	test_path_is_missing .git/index-helper.sock
+'
+
+test_done

@@ -571,6 +571,7 @@ extern void write_watchman_ext(struct strbuf *sb, struct index_state* istate);
 #define CLOSE_LOCK		(1 << 1)
 extern int write_locked_index(struct index_state *, struct lock_file *lock, unsigned flags);
 extern int discard_index(struct index_state *);
+extern void move_index_extensions(struct index_state *dst, struct index_state *src);
 extern int unmerged_index(const struct index_state *);
 extern int verify_path(const char *path);
 extern int index_dir_exists(struct index_state *istate, const char *name, int namelen);

@@ -2768,3 +2768,11 @@ 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;
+	dst->last_update = src->last_update;
+	src->last_update = NULL;
+}

@@ -646,4 +646,26 @@ test_expect_success 'test ident field is working' '
 	test_cmp ../expect ../err
 '
 
+test_expect_success 'untracked cache survives a checkout' '
+	git commit --allow-empty -m empty &&
+	test-dump-untracked-cache >../before &&
+	test_when_finished  "git checkout master" &&
+	git checkout -b other_branch &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after &&
+	test_commit test &&
+	test-dump-untracked-cache >../before &&
+	git checkout master &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after
+'
+
+test_expect_success 'untracked cache survives a commit' '
+	test-dump-untracked-cache >../before &&
+	git add done/two &&
+	git commit -m commit &&
+	test-dump-untracked-cache >../after &&
+	test_cmp ../before ../after
+'
+
 test_done

@@ -186,6 +186,10 @@ test_commit () {
 		test_tick
 	fi &&
 	git commit $signoff -m "$1" &&
+	if [ "$(git config core.bare)" = false ]
+	then
+	    git update-index --force-untracked-cache
+	fi
 	git tag "${4:-$1}"
 }
 

@@ -1215,6 +1215,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 						  WRITE_TREE_SILENT |
 						  WRITE_TREE_REPAIR);
 		}
+		move_index_extensions(&o->result, o->dst_index);
 		discard_index(o->dst_index);
 		*o->dst_index = o->result;
 	} else {

@@ -37,6 +37,9 @@ OPTIONS
 --detach::
 	Detach from the shell.
 
+--kill::
+	Kill any running index-helper and clean up the socket
+
 NOTES
 -----
 

@@ -378,6 +378,8 @@ static void loop(int fd, int idle_in_seconds)
 					 * alive, nothing to do.
 					 */
 				}
+			} else if (!strcmp(buf, "die")) {
+				break;
 			} else {
 				log_warning("BUG: Bogus command %s", buf);
 			}

@@ -408,10 +410,29 @@ static const char * const usage_text[] = {
 	NULL
 };
 
+static void request_kill(void)
+{
+	int fd = unix_stream_connect(git_path("index-helper.sock"));
+
+	if (fd >= 0) {
+		write_in_full(fd, "die", 4);
+		close(fd);
+	}
+
+	/*
+	 * The child will try to do this anyway, but we want to be
+	 * ready to launch a new daemon immediately after this command
+	 * returns.
+	 */
+
+	unlink(git_path("index-helper.sock"));
+	return;
+}
+
 int main(int argc, char **argv)
 {
 	const char *prefix;
-	int idle_in_seconds = 600, detach = 0;
+	int idle_in_seconds = 600, detach = 0, kill = 0;
 	int fd;
 	struct strbuf socket_path = STRBUF_INIT;
 	struct option options[] = {

@@ -420,6 +441,7 @@ int main(int argc, char **argv)
 		OPT_BOOL(0, "strict", &to_verify,
 			 "verify shared memory after creating"),
 		OPT_BOOL(0, "detach", &detach, "detach the process"),
+		OPT_BOOL(0, "kill", &kill, "request that existing index helper processes exit"),
 		OPT_END()
 	};
 

@@ -434,6 +456,13 @@ int main(int argc, char **argv)
 			  options, usage_text, 0))
 		die(_("too many arguments"));
 
+	if (kill) {
+		if (detach)
+			die(_("--kill doesn't want any other options"));
+		request_kill();
+		return 0;
+	}
+
 	atexit(cleanup);
 	sigchain_push_common(cleanup_on_signal);
 

@@ -20,4 +20,13 @@ test_expect_success 'index-helper smoke test' '
 	test_path_is_missing .git/index-helper.sock
 '
 
+test_expect_success 'index-helper creates usable path file and can be killed' '
+	test_when_finished "git index-helper --kill" &&
+	test_path_is_missing .git/index-helper.sock &&
+	git index-helper --detach &&
+	test -S .git/index-helper.sock &&
+	git index-helper --kill &&
+	test_path_is_missing .git/index-helper.sock
+'
+
 test_done

@@ -31,6 +31,9 @@ OPTIONS
 	for reading an index, but because it will happen in the
 	background, it's not noticable. `--strict` is enabled by default.
 
+--detach::
+	Detach from the shell.
+
 NOTES
 -----
 

@@ -17,7 +17,7 @@ struct shm {
 
 static struct shm shm_index;
 static struct shm shm_base_index;
-static int to_verify = 1;
+static int daemonized, to_verify = 1;
 
 static void log_warning(const char *warning, ...)
 {

@@ -59,6 +59,8 @@ static void cleanup_shm(void)
 
 static void cleanup(void)
 {
+	if (daemonized)
+		return;
 	unlink(git_path("index-helper.sock"));
 	cleanup_shm();
 }

@@ -318,7 +320,7 @@ static const char * const usage_text[] = {
 int main(int argc, char **argv)
 {
 	const char *prefix;
-	int idle_in_seconds = 600;
+	int idle_in_seconds = 600, detach = 0;
 	int fd;
 	struct strbuf socket_path = STRBUF_INIT;
 	struct option options[] = {

@@ -326,6 +328,7 @@ int main(int argc, char **argv)
 			    N_("exit if not used after some seconds")),
 		OPT_BOOL(0, "strict", &to_verify,
 			 "verify shared memory after creating"),
+		OPT_BOOL(0, "detach", &detach, "detach the process"),
 		OPT_END()
 	};
 

@@ -349,6 +352,14 @@ int main(int argc, char **argv)
 	if (fd < 0)
 		die_errno(_("could not set up index-helper socket"));
 
+	if (!freopen("/dev/null", "w", stderr))
+		die_errno("failed to redirect stderr to /dev/null");
+
+	if (!freopen("/dev/null", "w", stdout))
+		die_errno("failed to redirect stdout to /dev/null");
+
+	if (detach && daemonize(&daemonized))
+		die_errno(_("unable to detach"));
 	loop(fd, idle_in_seconds);
 
 	close(fd);

@@ -40,6 +40,10 @@ OPTIONS
 --kill::
 	Kill any running index-helper and clean up the socket
 
+--autorun::
+	If index-helper is not already running, start it.  Else, do
+	nothing.
+
 NOTES
 -----
 

@@ -432,8 +432,9 @@ static void request_kill(void)
 int main(int argc, char **argv)
 {
 	const char *prefix;
-	int idle_in_seconds = 600, detach = 0, kill = 0;
+	int idle_in_seconds = 600, detach = 0, kill = 0, autorun = 0;
 	int fd;
+	int nongit;
 	struct strbuf socket_path = STRBUF_INIT;
 	struct option options[] = {
 		OPT_INTEGER(0, "exit-after", &idle_in_seconds,

@@ -442,6 +443,7 @@ int main(int argc, char **argv)
 			 "verify shared memory after creating"),
 		OPT_BOOL(0, "detach", &detach, "detach the process"),
 		OPT_BOOL(0, "kill", &kill, "request that existing index helper processes exit"),
+		OPT_BOOL(0, "autorun", &autorun, "this is an automatic run of git index-helper, so certain errors can be solved by silently exiting"),
 		OPT_END()
 	};
 

@@ -451,7 +453,14 @@ int main(int argc, char **argv)
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage_with_options(usage_text, options);
 
-	prefix = setup_git_directory();
+	prefix = setup_git_directory_gently(&nongit);
+	if (nongit) {
+		if (autorun)
+			exit(0);
+		else
+			die(_("not a git repository"));
+	}
+
 	if (parse_options(argc, (const char **)argv, prefix,
 			  options, usage_text, 0))
 		die(_("too many arguments"));

@@ -465,10 +474,18 @@ int main(int argc, char **argv)
 
 	/* check that no other copy is running */
 	fd = unix_stream_connect(git_path("index-helper.sock"));
-	if (fd > 0)
-		die(_("Already running"));
-	if (errno != ECONNREFUSED && errno != ENOENT)
-		die_errno(_("Unexpected error checking socket"));
+	if (fd > 0) {
+		if (autorun)
+			exit(0);
+		else
+			die(_("Already running"));
+	}
+	if (errno != ECONNREFUSED && errno != ENOENT) {
+		if (autorun)
+			return 0;
+		else
+			die_errno(_("Unexpected error checking socket"));
+	}
 
 	atexit(cleanup);
 	sigchain_push_common(cleanup_on_signal);

@@ -38,4 +38,12 @@ test_expect_success 'index-helper will not start if already running' '
 	grep "Already running" err
 '
 
+test_expect_success 'index-helper is quiet with --autorun' '
+	test_when_finished "git index-helper --kill" &&
+	git index-helper --kill &&
+	git index-helper --detach &&
+	test -S .git/index-helper.sock &&
+	git index-helper --autorun
+'
+
 test_done

@@ -90,6 +90,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 	int diff_unmerged_stage = revs->max_count;
 	unsigned ce_option = ((option & DIFF_RACY_IS_MODIFIED)
 			      ? CE_MATCH_RACY_IS_DIRTY : 0);
+	uint64_t start = getnanotime();
 
 	diff_set_mnemonic_prefix(&revs->diffopt, "i/", "w/");
 

@@ -236,6 +237,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 	}
 	diffcore_std(&revs->diffopt);
 	diff_flush(&revs->diffopt);
+	trace_performance_since(start, "diff-files");
 	return 0;
 }
 

@@ -491,6 +493,7 @@ static int diff_cache(struct rev_info *revs,
 int run_diff_index(struct rev_info *revs, int cached)
 {
 	struct object_array_entry *ent;
+	uint64_t start = getnanotime();
 
 	ent = revs->pending.objects;
 	if (diff_cache(revs, ent->item->oid.hash, ent->name, cached))

@@ -500,6 +503,7 @@ int run_diff_index(struct rev_info *revs, int cached)
 	diffcore_fix_diff_index(&revs->diffopt);
 	diffcore_std(&revs->diffopt);
 	diff_flush(&revs->diffopt);
+	trace_performance_since(start, "diff-index");
 	return 0;
 }
 

@@ -2183,6 +2183,7 @@ int read_directory(struct dir_struct *dir, const char *path, int len, const stru
 {
 	struct path_simplify *simplify;
 	struct untracked_cache_dir *untracked;
+	uint64_t start = getnanotime();
 
 	/*
 	 * Check out create_simplify()

@@ -2224,6 +2225,7 @@ int read_directory(struct dir_struct *dir, const char *path, int len, const stru
 	free_simplify(simplify);
 	qsort(dir->entries, dir->nr, sizeof(struct dir_entry *), cmp_name);
 	qsort(dir->ignored, dir->ignored_nr, sizeof(struct dir_entry *), cmp_name);
+	trace_performance_since(start, "read directory %.*s", len, path);
 	if (dir->untracked) {
 		static struct trace_key trace_untracked_stats = TRACE_KEY_INIT(UNTRACKED_STATS);
 		trace_printf_key(&trace_untracked_stats,

@@ -115,6 +115,7 @@ static int cache_entry_cmp(const struct cache_entry *ce1,
 static void lazy_init_name_hash(struct index_state *istate)
 {
 	int nr;
+	uint64_t start = getnanotime();
 
 	if (istate->name_hash_initialized)
 		return;

@@ -124,6 +125,7 @@ static void lazy_init_name_hash(struct index_state *istate)
 	for (nr = 0; nr < istate->cache_nr; nr++)
 		hash_index_entry(istate, istate->cache[nr]);
 	istate->name_hash_initialized = 1;
+	trace_performance_since(start, "initialize name hash");
 }
 
 void add_name_hash(struct index_state *istate, struct cache_entry *ce)

@@ -72,6 +72,7 @@ static void preload_index(struct index_state *index,
 {
 	int threads, i, work, offset;
 	struct thread_data data[MAX_PARALLEL];
+	uint64_t start = getnanotime();
 
 	if (!core_preload_index)
 		return;

@@ -100,6 +101,7 @@ static void preload_index(struct index_state *index,
 		if (pthread_join(p->pthread, NULL))
 			die("unable to join threaded lstat");
 	}
+	trace_performance_since(start, "preload index");
 }
 #endif
 

@@ -1188,6 +1188,7 @@ 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");

@@ -1262,6 +1263,7 @@ int refresh_index(struct index_state *istate, unsigned int flags,
 
 		replace_index_entry(istate, i, new);
 	}
+	trace_performance_since(start, "refresh index");
 	return has_errors;
 }
 

@@ -2085,12 +2087,15 @@ int read_index_from(struct index_state *istate, const char *path)
 {
 	struct split_index *split_index;
 	int ret;
+	uint64_t start;
 
 	/* istate->initialized covers both .git/index and .git/sharedindex.xxx */
 	if (istate->initialized)
 		return istate->cache_nr;
 
+	start = getnanotime();
 	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)) {

@@ -2105,6 +2110,7 @@ int read_index_from(struct index_state *istate, const char *path)
 	split_index->base->keep_mmap = istate->keep_mmap;
 	split_index->base->to_shm    = istate->to_shm;
 	split_index->base->from_shm  = istate->from_shm;
+	start = getnanotime();
 	ret = do_read_index(split_index->base,
 			    git_path("sharedindex.%s",
 				     sha1_to_hex(split_index->base_sha1)), 1);

@@ -2116,6 +2122,9 @@ int read_index_from(struct index_state *istate, const char *path)
 		    sha1_to_hex(split_index->base->sha1));
 	merge_base_index(istate);
 	post_read_index_from(istate);
+	trace_performance_since(start, "read cache %s",
+				git_path("sharedindex.%s",
+					 sha1_to_hex(split_index->base_sha1)));
 
 done:
 	if (ret > 0 && istate->from_shm && istate->last_update)

@@ -2461,6 +2470,7 @@ static int do_write_index(struct index_state *istate, int newfd,
 	struct stat st;
 	struct strbuf previous_name_buf = STRBUF_INIT, *previous_name;
 	int watchman = 0;
+	uint64_t start = getnanotime();
 
 	for (i = removed = extended = 0; i < entries; i++) {
 		if (cache[i]->ce_flags & CE_REMOVE)

@@ -2581,6 +2591,7 @@ static int do_write_index(struct index_state *istate, int newfd,
 		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;
 }
 

@@ -1048,6 +1048,7 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
 	struct ref_entry *last = NULL;
 	struct strbuf line = STRBUF_INIT;
 	enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
+	uint64_t start = getnanotime();
 
 	while (strbuf_getwholeline(&line, f, '\n') != EOF) {
 		unsigned char sha1[20];

@@ -1096,6 +1097,7 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
 	}
 
 	strbuf_release(&line);
+	trace_performance_since(start, "read packed refs");
 }
 
 /*