Merge branch 'mh/write-refs-sooner-2.2' into mh/write-refs-sooner-2.3

* mh/write-refs-sooner-2.2:
  ref_transaction_commit(): fix atomicity and avoid fd exhaustion
  ref_transaction_commit(): remove the local flags variable
  ref_transaction_commit(): inline call to write_ref_sha1()
  rename_ref(): inline calls to write_ref_sha1() from this function
  commit_ref_update(): new function, extracted from write_ref_sha1()
  write_ref_to_lockfile(): new function, extracted from write_ref_sha1()
  t7004: rename ULIMIT test prerequisite to ULIMIT_STACK_SIZE
  update-ref: test handling large transactions properly

3 files changed, 103 insertions, 28 deletions

diff --git a/refs.c b/refs.c
index 3a26ad4e65..c689af6ccf 100644
--- a/refs.c
+++ b/refs.c
@@ -30,6 +30,13 @@ static unsigned char refname_disposition[256] = {
  * pruned.
  */
 #define REF_ISPRUNING	0x0100
+
+/*
+ * Used as a flag in ref_update::flags when the lockfile needs to be
+ * committed.
+ */
+#define REF_NEEDS_COMMIT 0x0200
+
 /*
  * Try to read one refname component from the front of refname.
  * Return the length of the component found, or -1 if the component is
@@ -2747,8 +2754,9 @@ static int rename_ref_available(const char *oldname, const char *newname)
 	return ret;
 }
 
-static int write_ref_sha1(struct ref_lock *lock, const unsigned char *sha1,
-			  const char *logmsg);
+static int write_ref_to_lockfile(struct ref_lock *lock, const unsigned char *sha1);
+static int commit_ref_update(struct ref_lock *lock,
+			     const unsigned char *sha1, const char *logmsg);
 
 int rename_ref(const char *oldrefname, const char *newrefname, const char *logmsg)
 {
@@ -2807,7 +2815,9 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 	}
 	lock->force_write = 1;
 	hashcpy(lock->old_sha1, orig_sha1);
-	if (write_ref_sha1(lock, orig_sha1, logmsg)) {
+
+	if (write_ref_to_lockfile(lock, orig_sha1) ||
+	    commit_ref_update(lock, orig_sha1, logmsg)) {
 		error("unable to write current sha1 into %s", newrefname);
 		goto rollback;
 	}
@@ -2824,7 +2834,8 @@ int rename_ref(const char *oldrefname, const char *newrefname, const char *logms
 	lock->force_write = 1;
 	flag = log_all_ref_updates;
 	log_all_ref_updates = 0;
-	if (write_ref_sha1(lock, orig_sha1, NULL))
+	if (write_ref_to_lockfile(lock, orig_sha1) ||
+	    commit_ref_update(lock, orig_sha1, NULL))
 		error("unable to write current sha1 into %s", oldrefname);
 	log_all_ref_updates = flag;
 
@@ -2996,23 +3007,15 @@ int is_branch(const char *refname)
 }
 
 /*
- * Write sha1 into the ref specified by the lock. Make sure that errno
- * is sane on error.
+ * Write sha1 into the open lockfile, then close the lockfile. On
+ * errors, rollback the lockfile and set errno to reflect the problem.
  */
-static int write_ref_sha1(struct ref_lock *lock,
-	const unsigned char *sha1, const char *logmsg)
+static int write_ref_to_lockfile(struct ref_lock *lock,
+				 const unsigned char *sha1)
 {
 	static char term = '\n';
 	struct object *o;
 
-	if (!lock) {
-		errno = EINVAL;
-		return -1;
-	}
-	if (!lock->force_write && !hashcmp(lock->old_sha1, sha1)) {
-		unlock_ref(lock);
-		return 0;
-	}
 	o = parse_object(sha1);
 	if (!o) {
 		error("Trying to write ref %s with nonexistent object %s",
@@ -3037,6 +3040,17 @@ static int write_ref_sha1(struct ref_lock *lock,
 		errno = save_errno;
 		return -1;
 	}
+	return 0;
+}
+
+/*
+ * Commit a change to a loose reference that has already been written
+ * to the loose reference lockfile. Also update the reflogs if
+ * necessary, using the specified lockmsg (which can be NULL).
+ */
+static int commit_ref_update(struct ref_lock *lock,
+			     const unsigned char *sha1, const char *logmsg)
+{
 	clear_loose_ref_cache(&ref_cache);
 	if (log_ref_write(lock->ref_name, lock->old_sha1, sha1, logmsg) < 0 ||
 	    (strcmp(lock->ref_name, lock->orig_ref_name) &&
@@ -3738,19 +3752,23 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 		goto cleanup;
 	}
 
-	/* Acquire all locks while verifying old values */
+	/*
+	 * Acquire all locks, verify old values if provided, check
+	 * that new values are valid, and write new values to the
+	 * lockfiles, ready to be activated. Only keep one lockfile
+	 * open at a time to avoid running out of file descriptors.
+	 */
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
-		int flags = update->flags;
 
 		if (is_null_sha1(update->new_sha1))
-			flags |= REF_DELETING;
+			update->flags |= REF_DELETING;
 		update->lock = lock_ref_sha1_basic(update->refname,
 						   (update->have_old ?
 						    update->old_sha1 :
 						    NULL),
 						   NULL,
-						   flags,
+						   update->flags,
 						   &update->type);
 		if (!update->lock) {
 			ret = (errno == ENOTDIR)
@@ -3760,22 +3778,51 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 				    update->refname);
 			goto cleanup;
 		}
+		if (!(update->flags & REF_DELETING) &&
+		    (update->lock->force_write ||
+		     hashcmp(update->lock->old_sha1, update->new_sha1))) {
+			if (write_ref_to_lockfile(update->lock, update->new_sha1)) {
+				/*
+				 * The lock was freed upon failure of
+				 * write_ref_to_lockfile():
+				 */
+				update->lock = NULL;
+				strbuf_addf(err, "Cannot update the ref '%s'.",
+					    update->refname);
+				ret = TRANSACTION_GENERIC_ERROR;
+				goto cleanup;
+			}
+			update->flags |= REF_NEEDS_COMMIT;
+		} else {
+			/*
+			 * We didn't have to write anything to the lockfile.
+			 * Close it to free up the file descriptor:
+			 */
+			if (close_ref(update->lock)) {
+				strbuf_addf(err, "Couldn't close %s.lock",
+					    update->refname);
+				goto cleanup;
+			}
+		}
 	}
 
 	/* Perform updates first so live commits remain referenced */
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
-		if (!is_null_sha1(update->new_sha1)) {
-			if (write_ref_sha1(update->lock, update->new_sha1,
-					   update->msg)) {
-				update->lock = NULL; /* freed by write_ref_sha1 */
+		if (update->flags & REF_NEEDS_COMMIT) {
+			if (commit_ref_update(update->lock,
+					      update->new_sha1, update->msg)) {
+				/* The lock was freed by commit_ref_update(): */
+				update->lock = NULL;
 				strbuf_addf(err, "Cannot update the ref '%s'.",
 					    update->refname);
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto cleanup;
+			} else {
+				/* freed by the above call: */
+				update->lock = NULL;
 			}
-			update->lock = NULL; /* freed by write_ref_sha1 */
 		}
 	}
 
@@ -3783,7 +3830,7 @@ int ref_transaction_commit(struct ref_transaction *transaction,
 	for (i = 0; i < n; i++) {
 		struct ref_update *update = updates[i];
 
-		if (update->lock) {
+		if (update->flags & REF_DELETING) {
 			if (delete_ref_loose(update->lock, update->type, err)) {
 				ret = TRANSACTION_GENERIC_ERROR;
 				goto cleanup;
diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index 6805b9e6bb..636d3a167c 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -1065,4 +1065,32 @@ test_expect_success 'stdin -z delete refs works with packed and loose refs' '
 	test_must_fail git rev-parse --verify -q $c
 '
 
+run_with_limited_open_files () {
+	(ulimit -n 32 && "$@")
+}
+
+test_lazy_prereq ULIMIT_FILE_DESCRIPTORS 'run_with_limited_open_files true'
+
+test_expect_success ULIMIT_FILE_DESCRIPTORS 'large transaction creating branches does not burst open file limit' '
+(
+	for i in $(test_seq 33)
+	do
+		echo "create refs/heads/$i HEAD"
+	done >large_input &&
+	run_with_limited_open_files git update-ref --stdin <large_input &&
+	git rev-parse --verify -q refs/heads/33
+)
+'
+
+test_expect_success ULIMIT_FILE_DESCRIPTORS 'large transaction deleting branches does not burst open file limit' '
+(
+	for i in $(test_seq 33)
+	do
+		echo "delete refs/heads/$i HEAD"
+	done >large_input &&
+	run_with_limited_open_files git update-ref --stdin <large_input &&
+	test_must_fail git rev-parse --verify -q refs/heads/33
+)
+'
+
 test_done
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index 35c805a44e..5446060ffb 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -1463,10 +1463,10 @@ run_with_limited_stack () {
 	(ulimit -s 128 && "$@")
 }
 
-test_lazy_prereq ULIMIT 'run_with_limited_stack true'
+test_lazy_prereq ULIMIT_STACK_SIZE 'run_with_limited_stack true'
 
 # we require ulimit, this excludes Windows
-test_expect_success ULIMIT '--contains works in a deep repo' '
+test_expect_success ULIMIT_STACK_SIZE '--contains works in a deep repo' '
 	>expect &&
 	i=1 &&
 	while test $i -lt 8000