Remove pack.keep after ref updates in git-fetch

If we are using a native packfile to perform a git-fetch invocation
and the received packfile contained more than the configured limits
of fetch.unpackLimit/transfer.unpackLimit then index-pack will output
a single line saying "keep\t$sha1\n" to stdout.  This line needs to
be captured and retained so we can delete the corresponding .keep
file ("$GIT_DIR/objects/pack/pack-$sha1.keep") once all refs have
been safely updated.

This trick has long been in use with git-fetch.sh and its lower level
helper git-fetch--tool as a way to allow index-pack to save the new
packfile before the refs have been updated and yet avoid a race with
any concurrently running git-repack process.  It was unfortunately
lost when git-fetch.sh was converted to pure C and fetch--tool was
no longer being invoked.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-fetch-pack.c

@@ -493,7 +493,7 @@ static pid_t setup_sideband(int fd[2], int xd[2])
 	return side_pid;
 }
 
-static int get_pack(int xd[2])
+static int get_pack(int xd[2], char **pack_lockfile)
 {
 	int status;
 	pid_t pid, side_pid;
@@ -503,6 +503,7 @@ static int get_pack(int xd[2])
 	char hdr_arg[256];
 	const char **av;
 	int do_keep = keep_pack;
+	int keep_pipe[2];
 
 	side_pid = setup_sideband(fd, xd);
 
@@ -522,6 +523,8 @@ static int get_pack(int xd[2])
 	}
 
 	if (do_keep) {
+		if (pack_lockfile && pipe(keep_pipe))
+			die("fetch-pack: pipe setup failure: %s", strerror(errno));
 		*av++ = "index-pack";
 		*av++ = "--stdin";
 		if (!quiet && !no_progress)
@@ -550,13 +553,23 @@ static int get_pack(int xd[2])
 		die("fetch-pack: unable to fork off %s", argv[0]);
 	if (!pid) {
 		dup2(fd[0], 0);
+		if (do_keep && pack_lockfile) {
+			dup2(keep_pipe[1], 1);
+			close(keep_pipe[0]);
+			close(keep_pipe[1]);
+		}
 		close(fd[0]);
 		close(fd[1]);
 		execv_git_cmd(argv);
 		die("%s exec failed", argv[0]);
 	}
 	close(fd[0]);
 	close(fd[1]);
+	if (do_keep && pack_lockfile) {
+		close(keep_pipe[1]);
+		*pack_lockfile = index_pack_lockfile(keep_pipe[0]);
+		close(keep_pipe[0]);
+	}
 	while (waitpid(pid, &status, 0) < 0) {
 		if (errno != EINTR)
 			die("waiting for %s: %s", argv[0], strerror(errno));
@@ -574,7 +587,10 @@ static int get_pack(int xd[2])
 	die("%s died of unnatural causes %d", argv[0], status);
 }
 
-static struct ref *do_fetch_pack(int fd[2], int nr_match, char **match)
+static struct ref *do_fetch_pack(int fd[2],
+		int nr_match,
+		char **match,
+		char **pack_lockfile)
 {
 	struct ref *ref;
 	unsigned char sha1[20];
@@ -612,7 +628,7 @@ static struct ref *do_fetch_pack(int fd[2], int nr_match, char **match)
 			 */
 			fprintf(stderr, "warning: no common commits\n");
 
-	if (get_pack(fd))
+	if (get_pack(fd, pack_lockfile))
 		die("git-fetch-pack: fetch failed.");
 
  all_done:
@@ -741,7 +757,7 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	if (!dest)
 		usage(fetch_pack_usage);
 
-	ref = fetch_pack(dest, nr_heads, heads);
+	ref = fetch_pack(dest, nr_heads, heads, NULL);
 
 	ret = !ref;
 
@@ -754,7 +770,10 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	return ret;
 }
 
-struct ref *fetch_pack(const char *dest, int nr_heads, char **heads)
+struct ref *fetch_pack(const char *dest,
+		int nr_heads,
+		char **heads,
+		char **pack_lockfile)
 {
 	int i, ret;
 	int fd[2];
@@ -773,7 +792,7 @@ struct ref *fetch_pack(const char *dest, int nr_heads, char **heads)
 		return NULL;
 	if (heads && nr_heads)
 		nr_heads = remove_duplicates(nr_heads, heads);
-	ref = do_fetch_pack(fd, nr_heads, heads);
+	ref = do_fetch_pack(fd, nr_heads, heads, pack_lockfile);
 	close(fd[0]);
 	close(fd[1]);
 	ret = finish_connect(pid);

builtin-fetch.c

@@ -274,6 +274,7 @@ static int fetch_refs(struct transport *transport, struct ref *ref_map)
 	int ret = transport_fetch_refs(transport, ref_map);
 	if (!ret)
 		store_updated_refs(transport->url, ref_map);
+	transport_unlock_pack(transport);
 	return ret;
 }
 

fetch-pack.h

@@ -16,6 +16,6 @@ struct fetch_pack_args
 
 void setup_fetch_pack(struct fetch_pack_args *args);
 
-struct ref *fetch_pack(const char *dest, int nr_heads, char **heads);
+struct ref *fetch_pack(const char *dest, int nr_heads, char **heads, char **pack_lockfile);
 
 #endif

transport.c

@@ -9,7 +9,7 @@
 
 /* Generic functions for using commit walkers */
 
-static int fetch_objs_via_walker(const struct transport *transport,
+static int fetch_objs_via_walker(struct transport *transport,
 				 int nr_objs, struct ref **to_fetch)
 {
 	char *dest = xstrdup(transport->url);
@@ -219,7 +219,7 @@ static struct ref *get_refs_from_bundle(const struct transport *transport)
 	return result;
 }
 
-static int fetch_refs_from_bundle(const struct transport *transport,
+static int fetch_refs_from_bundle(struct transport *transport,
 			       int nr_heads, struct ref **to_fetch)
 {
 	struct bundle_transport_data *data = transport->data;
@@ -306,7 +306,7 @@ static struct ref *get_refs_via_connect(const struct transport *transport)
 	return refs;
 }
 
-static int fetch_refs_via_pack(const struct transport *transport,
+static int fetch_refs_via_pack(struct transport *transport,
 			       int nr_heads, struct ref **to_fetch)
 {
 	struct git_transport_data *data = transport->data;
@@ -330,7 +330,7 @@ static int fetch_refs_via_pack(const struct transport *transport,
 
 	for (i = 0; i < nr_heads; i++)
 		heads[i] = xstrdup(to_fetch[i]->name);
-	refs = fetch_pack(dest, nr_heads, heads);
+	refs = fetch_pack(dest, nr_heads, heads, &transport->pack_lockfile);
 
 	for (i = 0; i < nr_heads; i++)
 		free(heads[i]);
@@ -445,6 +445,7 @@ struct transport *transport_get(struct remote *remote, const char *url,
 		ret->url = url;
 		ret->remote_refs = NULL;
 		ret->fetch = !!fetch;
+		ret->pack_lockfile = NULL;
 	}
 	return ret;
 }
@@ -500,6 +501,15 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs)
 	return rc;
 }
 
+void transport_unlock_pack(struct transport *transport)
+{
+	if (transport->pack_lockfile) {
+		unlink(transport->pack_lockfile);
+		free(transport->pack_lockfile);
+		transport->pack_lockfile = NULL;
+	}
+}
+
 int transport_disconnect(struct transport *transport)
 {
 	int ret = 0;

transport.h

@@ -15,6 +15,7 @@ struct transport {
 	struct ref *remote_refs;
 
 	const struct transport_ops *ops;
+	char *pack_lockfile;
 };
 
 #define TRANSPORT_PUSH_ALL 1
@@ -30,7 +31,7 @@ struct transport_ops {
 			  const char *value);
 
 	struct ref *(*get_refs_list)(const struct transport *transport);
-	int (*fetch)(const struct transport *transport, int refs_nr, struct ref **refs);
+	int (*fetch)(struct transport *transport, int refs_nr, struct ref **refs);
 	int (*push)(struct transport *connection, int refspec_nr, const char **refspec, int flags);
 
 	int (*disconnect)(struct transport *connection);
@@ -73,7 +74,7 @@ int transport_push(struct transport *connection,
 struct ref *transport_get_remote_refs(struct transport *transport);
 
 int transport_fetch_refs(struct transport *transport, struct ref *refs);
-
+void transport_unlock_pack(struct transport *transport);
 int transport_disconnect(struct transport *transport);
 
 #endif