Merge branch 'mh/ref-directory-file'
authorJunio C Hamano <gitster@pobox.com>
Fri, 22 May 2015 19:41:53 +0000 (12:41 -0700)
committerJunio C Hamano <gitster@pobox.com>
Fri, 22 May 2015 19:41:53 +0000 (12:41 -0700)
The ref API did not handle cases where 'refs/heads/xyzzy/frotz' is
removed at the same time as 'refs/heads/xyzzy' is added (or vice
versa) very well.

* mh/ref-directory-file:
reflog_expire(): integrate lock_ref_sha1_basic() errors into ours
ref_transaction_commit(): delete extra "the" from error message
ref_transaction_commit(): provide better error messages
rename_ref(): integrate lock_ref_sha1_basic() errors into ours
lock_ref_sha1_basic(): improve diagnostics for ref D/F conflicts
lock_ref_sha1_basic(): report errors via a "struct strbuf *err"
verify_refname_available(): report errors via a "struct strbuf *err"
verify_refname_available(): rename function
refs: check for D/F conflicts among refs created in a transaction
ref_transaction_commit(): use a string_list for detecting duplicates
is_refname_available(): use dirname in first loop
struct nonmatching_ref_data: store a refname instead of a ref_entry
report_refname_conflict(): inline function
entry_matches(): inline function
is_refname_available(): convert local variable "dirname" to strbuf
is_refname_available(): avoid shadowing "dir" variable
is_refname_available(): revamp the comments
t1404: new tests of ref D/F conflicts within transactions

1  2 
refs.c
t/t1400-update-ref.sh
diff --combined refs.c
index 825a1f6847ccefb3aba29e489c05c96382fff907,97043fd2ef88fd50dadf05d673bb80018d3caf06..f704ee285cdff46e94d9bd47de5f39a7cc6927ee
--- 1/refs.c
--- 2/refs.c
+++ b/refs.c
@@@ -11,6 -11,7 +11,6 @@@ struct ref_lock 
        char *orig_ref_name;
        struct lock_file *lk;
        unsigned char old_sha1[20];
 -      int lock_fd;
  };
  
  /*
@@@ -56,12 -57,6 +56,12 @@@ static unsigned char refname_dispositio
   */
  #define REF_HAVE_OLD  0x10
  
 +/*
 + * Used as a flag in ref_update::flags when the lockfile needs to be
 + * committed.
 + */
 +#define REF_NEEDS_COMMIT 0x20
 +
  /*
   * Try to read one refname component from the front of refname.
   * Return the length of the component found, or -1 if the component is
@@@ -268,7 -263,7 +268,7 @@@ struct ref_dir 
   * presence of an empty subdirectory does not block the creation of a
   * similarly-named reference.  (The fact that reference names with the
   * same leading components can conflict *with each other* is a
-  * separate issue that is regulated by is_refname_available().)
+  * separate issue that is regulated by verify_refname_available().)
   *
   * Please note that the name field contains the fully-qualified
   * reference (or subdirectory) name.  Space could be saved by only
@@@ -349,6 -344,8 +349,6 @@@ static struct ref_entry *create_ref_ent
        if (check_name &&
            check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
                die("Reference has invalid format: '%s'", refname);
 -      if (!check_name && !refname_is_safe(refname))
 -              die("Reference has invalid name: '%s'", refname);
        len = strlen(refname) + 1;
        ref = xmalloc(sizeof(struct ref_entry) + len);
        hashcpy(ref->u.value.sha1, sha1);
@@@ -844,121 -841,181 +844,181 @@@ static void prime_ref_dir(struct ref_di
        }
  }
  
- static int entry_matches(struct ref_entry *entry, const struct string_list *list)
- {
-       return list && string_list_has_string(list, entry->name);
- }
  struct nonmatching_ref_data {
        const struct string_list *skip;
-       struct ref_entry *found;
+       const char *conflicting_refname;
  };
  
  static int nonmatching_ref_fn(struct ref_entry *entry, void *vdata)
  {
        struct nonmatching_ref_data *data = vdata;
  
-       if (entry_matches(entry, data->skip))
+       if (data->skip && string_list_has_string(data->skip, entry->name))
                return 0;
  
-       data->found = entry;
+       data->conflicting_refname = entry->name;
        return 1;
  }
  
- static void report_refname_conflict(struct ref_entry *entry,
-                                   const char *refname)
- {
-       error("'%s' exists; cannot create '%s'", entry->name, refname);
- }
  /*
-  * Return true iff a reference named refname could be created without
-  * conflicting with the name of an existing reference in dir.  If
-  * skip is non-NULL, ignore potential conflicts with refs in skip
-  * (e.g., because they are scheduled for deletion in the same
-  * operation).
+  * Return 0 if a reference named refname could be created without
+  * conflicting with the name of an existing reference in dir.
+  * Otherwise, return a negative value and write an explanation to err.
+  * If extras is non-NULL, it is a list of additional refnames with
+  * which refname is not allowed to conflict. If skip is non-NULL,
+  * ignore potential conflicts with refs in skip (e.g., because they
+  * are scheduled for deletion in the same operation). Behavior is
+  * undefined if the same name is listed in both extras and skip.
   *
   * Two reference names conflict if one of them exactly matches the
-  * leading components of the other; e.g., "foo/bar" conflicts with
-  * both "foo" and with "foo/bar/baz" but not with "foo/bar" or
-  * "foo/barbados".
+  * leading components of the other; e.g., "refs/foo/bar" conflicts
+  * with both "refs/foo" and with "refs/foo/bar/baz" but not with
+  * "refs/foo/bar" or "refs/foo/barbados".
   *
-  * skip must be sorted.
+  * extras and skip must be sorted.
   */
- static int is_refname_available(const char *refname,
-                               const struct string_list *skip,
-                               struct ref_dir *dir)
+ static int verify_refname_available(const char *refname,
+                                   const struct string_list *extras,
+                                   const struct string_list *skip,
+                                   struct ref_dir *dir,
+                                   struct strbuf *err)
  {
        const char *slash;
-       size_t len;
        int pos;
-       char *dirname;
+       struct strbuf dirname = STRBUF_INIT;
+       int ret = -1;
+       /*
+        * For the sake of comments in this function, suppose that
+        * refname is "refs/foo/bar".
+        */
  
+       assert(err);
+       strbuf_grow(&dirname, strlen(refname) + 1);
        for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
+               /* Expand dirname to the new prefix, not including the trailing slash: */
+               strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
                /*
-                * We are still at a leading dir of the refname; we are
-                * looking for a conflict with a leaf entry.
-                *
-                * If we find one, we still must make sure it is
-                * not in "skip".
+                * We are still at a leading dir of the refname (e.g.,
+                * "refs/foo"; if there is a reference with that name,
+                * it is a conflict, *unless* it is in skip.
                 */
-               pos = search_ref_dir(dir, refname, slash - refname);
-               if (pos >= 0) {
-                       struct ref_entry *entry = dir->entries[pos];
-                       if (entry_matches(entry, skip))
-                               return 1;
-                       report_refname_conflict(entry, refname);
-                       return 0;
+               if (dir) {
+                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
+                       if (pos >= 0 &&
+                           (!skip || !string_list_has_string(skip, dirname.buf))) {
+                               /*
+                                * We found a reference whose name is
+                                * a proper prefix of refname; e.g.,
+                                * "refs/foo", and is not in skip.
+                                */
+                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
+                                           dirname.buf, refname);
+                               goto cleanup;
+                       }
                }
  
+               if (extras && string_list_has_string(extras, dirname.buf) &&
+                   (!skip || !string_list_has_string(skip, dirname.buf))) {
+                       strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
+                                   refname, dirname.buf);
+                       goto cleanup;
+               }
  
                /*
                 * Otherwise, we can try to continue our search with
-                * the next component; if we come up empty, we know
-                * there is nothing under this whole prefix.
+                * the next component. So try to look up the
+                * directory, e.g., "refs/foo/". If we come up empty,
+                * we know there is nothing under this whole prefix,
+                * but even in that case we still have to continue the
+                * search for conflicts with extras.
                 */
-               pos = search_ref_dir(dir, refname, slash + 1 - refname);
-               if (pos < 0)
-                       return 1;
-               dir = get_ref_dir(dir->entries[pos]);
+               strbuf_addch(&dirname, '/');
+               if (dir) {
+                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
+                       if (pos < 0) {
+                               /*
+                                * There was no directory "refs/foo/",
+                                * so there is nothing under this
+                                * whole prefix. So there is no need
+                                * to continue looking for conflicting
+                                * references. But we need to continue
+                                * looking for conflicting extras.
+                                */
+                               dir = NULL;
+                       } else {
+                               dir = get_ref_dir(dir->entries[pos]);
+                       }
+               }
        }
  
        /*
-        * We are at the leaf of our refname; we want to
-        * make sure there are no directories which match it.
+        * We are at the leaf of our refname (e.g., "refs/foo/bar").
+        * There is no point in searching for a reference with that
+        * name, because a refname isn't considered to conflict with
+        * itself. But we still need to check for references whose
+        * names are in the "refs/foo/bar/" namespace, because they
+        * *do* conflict.
         */
-       len = strlen(refname);
-       dirname = xmallocz(len + 1);
-       sprintf(dirname, "%s/", refname);
-       pos = search_ref_dir(dir, dirname, len + 1);
-       free(dirname);
+       strbuf_addstr(&dirname, refname + dirname.len);
+       strbuf_addch(&dirname, '/');
+       if (dir) {
+               pos = search_ref_dir(dir, dirname.buf, dirname.len);
  
-       if (pos >= 0) {
+               if (pos >= 0) {
+                       /*
+                        * We found a directory named "$refname/"
+                        * (e.g., "refs/foo/bar/"). It is a problem
+                        * iff it contains any ref that is not in
+                        * "skip".
+                        */
+                       struct nonmatching_ref_data data;
+                       data.skip = skip;
+                       data.conflicting_refname = NULL;
+                       dir = get_ref_dir(dir->entries[pos]);
+                       sort_ref_dir(dir);
+                       if (do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data)) {
+                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
+                                           data.conflicting_refname, refname);
+                               goto cleanup;
+                       }
+               }
+       }
+       if (extras) {
                /*
-                * We found a directory named "refname". It is a
-                * problem iff it contains any ref that is not
-                * in "skip".
+                * Check for entries in extras that start with
+                * "$refname/". We do that by looking for the place
+                * where "$refname/" would be inserted in extras. If
+                * there is an entry at that position that starts with
+                * "$refname/" and is not in skip, then we have a
+                * conflict.
                 */
-               struct ref_entry *entry = dir->entries[pos];
-               struct ref_dir *dir = get_ref_dir(entry);
-               struct nonmatching_ref_data data;
+               for (pos = string_list_find_insert_index(extras, dirname.buf, 0);
+                    pos < extras->nr; pos++) {
+                       const char *extra_refname = extras->items[pos].string;
  
-               data.skip = skip;
-               sort_ref_dir(dir);
-               if (!do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data))
-                       return 1;
+                       if (!starts_with(extra_refname, dirname.buf))
+                               break;
  
-               report_refname_conflict(data.found, refname);
-               return 0;
+                       if (!skip || !string_list_has_string(skip, extra_refname)) {
+                               strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
+                                           refname, extra_refname);
+                               goto cleanup;
+                       }
+               }
        }
  
-       /*
-        * There is no point in searching for another leaf
-        * node which matches it; such an entry would be the
-        * ref we are looking for, not a conflict.
-        */
-       return 1;
+       /* No conflicts were found */
+       ret = 0;
+ cleanup:
+       strbuf_release(&dirname);
+       return ret;
  }
  
  struct packed_ref_cache {
@@@ -1181,8 -1238,6 +1241,8 @@@ static void read_packed_refs(FILE *f, s
                        int flag = REF_ISPACKED;
  
                        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 +                              if (!refname_is_safe(refname))
 +                                      die("packed refname is dangerous: %s", refname);
                                hashclr(sha1);
                                flag |= REF_BAD_NAME | REF_ISBROKEN;
                        }
@@@ -1328,8 -1383,6 +1388,8 @@@ static void read_loose_refs(const char 
                        }
                        if (check_refname_format(refname.buf,
                                                 REFNAME_ALLOW_ONELEVEL)) {
 +                              if (!refname_is_safe(refname.buf))
 +                                      die("loose refname is dangerous: %s", refname.buf);
                                hashclr(sha1);
                                flag |= REF_BAD_NAME | REF_ISBROKEN;
                        }
@@@ -1389,7 -1442,7 +1449,7 @@@ static int resolve_gitlink_ref_recursiv
  {
        int fd, len;
        char buffer[128], *p;
 -      char *path;
 +      const char *path;
  
        if (recursion > MAXDEPTH || strlen(refname) > MAXREFLEN)
                return -1;
@@@ -1482,11 -1535,7 +1542,11 @@@ static int resolve_missing_loose_ref(co
  }
  
  /* This function needs to return a meaningful errno on failure */
 -const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned char *sha1, int *flags)
 +static const char *resolve_ref_unsafe_1(const char *refname,
 +                                      int resolve_flags,
 +                                      unsigned char *sha1,
 +                                      int *flags,
 +                                      struct strbuf *sb_path)
  {
        int depth = MAXDEPTH;
        ssize_t len;
                bad_name = 1;
        }
        for (;;) {
 -              char path[PATH_MAX];
 +              const char *path;
                struct stat st;
                char *buf;
                int fd;
                        return NULL;
                }
  
 -              git_snpath(path, sizeof(path), "%s", refname);
 +              strbuf_reset(sb_path);
 +              strbuf_git_path(sb_path, "%s", refname);
 +              path = sb_path->buf;
  
                /*
                 * We might have to loop back here to avoid a race
        }
  }
  
 +const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
 +                             unsigned char *sha1, int *flags)
 +{
 +      struct strbuf sb_path = STRBUF_INIT;
 +      const char *ret = resolve_ref_unsafe_1(refname, resolve_flags,
 +                                             sha1, flags, &sb_path);
 +      strbuf_release(&sb_path);
 +      return ret;
 +}
 +
  char *resolve_refdup(const char *ref, int resolve_flags, unsigned char *sha1, int *flags)
  {
        return xstrdup_or_null(resolve_ref_unsafe(ref, resolve_flags, sha1, flags));
@@@ -2294,10 -2331,12 +2354,12 @@@ int dwim_log(const char *str, int len, 
   */
  static struct ref_lock *lock_ref_sha1_basic(const char *refname,
                                            const unsigned char *old_sha1,
+                                           const struct string_list *extras,
                                            const struct string_list *skip,
-                                           unsigned int flags, int *type_p)
+                                           unsigned int flags, int *type_p,
+                                           struct strbuf *err)
  {
 -      char *ref_file;
 +      const char *ref_file;
        const char *orig_refname = refname;
        struct ref_lock *lock;
        int last_errno = 0;
        int resolve_flags = 0;
        int attempts_remaining = 3;
  
+       assert(err);
        lock = xcalloc(1, sizeof(struct ref_lock));
 -      lock->lock_fd = -1;
  
        if (mustexist)
                resolve_flags |= RESOLVE_REF_READING;
                ref_file = git_path("%s", orig_refname);
                if (remove_empty_directories(ref_file)) {
                        last_errno = errno;
-                       error("there are still refs under '%s'", orig_refname);
+                       if (!verify_refname_available(orig_refname, extras, skip,
+                                                     get_loose_refs(&ref_cache), err))
+                               strbuf_addf(err, "there are still refs under '%s'",
+                                           orig_refname);
                        goto error_return;
                }
                refname = resolve_ref_unsafe(orig_refname, resolve_flags,
            *type_p = type;
        if (!refname) {
                last_errno = errno;
-               error("unable to resolve reference %s: %s",
-                       orig_refname, strerror(errno));
+               if (last_errno != ENOTDIR ||
+                   !verify_refname_available(orig_refname, extras, skip,
+                                             get_loose_refs(&ref_cache), err))
+                       strbuf_addf(err, "unable to resolve reference %s: %s",
+                                   orig_refname, strerror(last_errno));
                goto error_return;
        }
        /*
         * our refname.
         */
        if (is_null_sha1(lock->old_sha1) &&
-            !is_refname_available(refname, skip, get_packed_refs(&ref_cache))) {
+           verify_refname_available(refname, extras, skip,
+                                    get_packed_refs(&ref_cache), err)) {
                last_errno = ENOTDIR;
                goto error_return;
        }
        ref_file = git_path("%s", refname);
  
   retry:
 -      switch (safe_create_leading_directories(ref_file)) {
 +      switch (safe_create_leading_directories_const(ref_file)) {
        case SCLD_OK:
                break; /* success */
        case SCLD_VANISHED:
                /* fall through */
        default:
                last_errno = errno;
-               error("unable to create directory for %s", ref_file);
+               strbuf_addf(err, "unable to create directory for %s", ref_file);
                goto error_return;
        }
  
 -      lock->lock_fd = hold_lock_file_for_update(lock->lk, ref_file, lflags);
 -      if (lock->lock_fd < 0) {
 +      if (hold_lock_file_for_update(lock->lk, ref_file, lflags) < 0) {
                last_errno = errno;
                if (errno == ENOENT && --attempts_remaining > 0)
                        /*
                         */
                        goto retry;
                else {
-                       struct strbuf err = STRBUF_INIT;
-                       unable_to_lock_message(ref_file, errno, &err);
-                       error("%s", err.buf);
-                       strbuf_release(&err);
+                       unable_to_lock_message(ref_file, errno, err);
                        goto error_return;
                }
        }
@@@ -2742,7 -2792,7 +2813,7 @@@ static int rename_tmp_log(const char *n
        int attempts_remaining = 4;
  
   retry:
 -      switch (safe_create_leading_directories(git_path("logs/%s", newrefname))) {
 +      switch (safe_create_leading_directories_const(git_path("logs/%s", newrefname))) {
        case SCLD_OK:
                break; /* success */
        case SCLD_VANISHED:
  static int rename_ref_available(const char *oldname, const char *newname)
  {
        struct string_list skip = STRING_LIST_INIT_NODUP;
+       struct strbuf err = STRBUF_INIT;
        int ret;
  
        string_list_insert(&skip, oldname);
-       ret = is_refname_available(newname, &skip, get_packed_refs(&ref_cache))
-           && is_refname_available(newname, &skip, get_loose_refs(&ref_cache));
+       ret = !verify_refname_available(newname, NULL, &skip,
+                                       get_packed_refs(&ref_cache), &err)
+               && !verify_refname_available(newname, NULL, &skip,
+                                            get_loose_refs(&ref_cache), &err);
+       if (!ret)
+               error("%s", err.buf);
        string_list_clear(&skip, 0);
+       strbuf_release(&err);
        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)
  {
        struct stat loginfo;
        int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
        const char *symref = NULL;
+       struct strbuf err = STRBUF_INIT;
  
        if (log && S_ISLNK(loginfo.st_mode))
                return error("reflog for %s is a symlink", oldrefname);
  
        logmoved = log;
  
-       lock = lock_ref_sha1_basic(newrefname, NULL, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(newrefname, NULL, NULL, NULL, 0, NULL, &err);
        if (!lock) {
-               error("unable to lock %s for update", newrefname);
+               error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+               strbuf_release(&err);
                goto rollback;
        }
        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;
        }
        return 0;
  
   rollback:
-       lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, 0, NULL);
+       lock = lock_ref_sha1_basic(oldrefname, NULL, NULL, NULL, 0, NULL, &err);
        if (!lock) {
-               error("unable to lock %s for rollback", oldrefname);
+               error("unable to lock %s for rollback: %s", oldrefname, err.buf);
+               strbuf_release(&err);
                goto rollbacklog;
        }
  
        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;
  
@@@ -2893,6 -2949,7 +2974,6 @@@ static int close_ref(struct ref_lock *l
  {
        if (close_lock_file(lock->lk))
                return -1;
 -      lock->lock_fd = -1;
        return 0;
  }
  
@@@ -2900,6 -2957,7 +2981,6 @@@ static int commit_ref(struct ref_lock *
  {
        if (commit_lock_file(lock->lk))
                return -1;
 -      lock->lock_fd = -1;
        return 0;
  }
  
@@@ -2930,15 -2988,11 +3011,15 @@@ static int copy_msg(char *buf, const ch
  }
  
  /* This function must set a meaningful errno on failure */
 -int log_ref_setup(const char *refname, char *logfile, int bufsize)
 +int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
  {
        int logfd, oflags = O_APPEND | O_WRONLY;
 +      char *logfile;
  
 -      git_snpath(logfile, bufsize, "logs/%s", refname);
 +      strbuf_git_path(sb_logfile, "logs/%s", refname);
 +      logfile = sb_logfile->buf;
 +      /* make sure the rest of the function can't change "logfile" */
 +      sb_logfile = NULL;
        if (log_all_ref_updates &&
            (starts_with(refname, "refs/heads/") ||
             starts_with(refname, "refs/remotes/") ||
@@@ -3009,22 -3063,18 +3090,22 @@@ static int log_ref_write_fd(int fd, con
        return 0;
  }
  
 -static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 -                       const unsigned char *new_sha1, const char *msg)
 +static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
 +                         const unsigned char *new_sha1, const char *msg,
 +                         struct strbuf *sb_log_file)
  {
        int logfd, result, oflags = O_APPEND | O_WRONLY;
 -      char log_file[PATH_MAX];
 +      char *log_file;
  
        if (log_all_ref_updates < 0)
                log_all_ref_updates = !is_bare_repository();
  
 -      result = log_ref_setup(refname, log_file, sizeof(log_file));
 +      result = log_ref_setup(refname, sb_log_file);
        if (result)
                return result;
 +      log_file = sb_log_file->buf;
 +      /* make sure the rest of the function can't change "log_file" */
 +      sb_log_file = NULL;
  
        logfd = open(log_file, oflags);
        if (logfd < 0)
        return 0;
  }
  
 +static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 +                       const unsigned char *new_sha1, const char *msg)
 +{
 +      struct strbuf sb = STRBUF_INIT;
 +      int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb);
 +      strbuf_release(&sb);
 +      return ret;
 +}
 +
  int is_branch(const char *refname)
  {
        return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
  }
  
  /*
 - * 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;
                errno = EINVAL;
                return -1;
        }
 -      if (write_in_full(lock->lock_fd, sha1_to_hex(sha1), 40) != 40 ||
 -          write_in_full(lock->lock_fd, &term, 1) != 1 ||
 +      if (write_in_full(lock->lk->fd, sha1_to_hex(sha1), 40) != 40 ||
 +          write_in_full(lock->lk->fd, &term, 1) != 1 ||
            close_ref(lock) < 0) {
                int save_errno = errno;
                error("Couldn't write %s", lock->lk->filename.buf);
                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) &&
@@@ -3746,25 -3776,18 +3827,18 @@@ int update_ref(const char *msg, const c
        return 0;
  }
  
- static int ref_update_compare(const void *r1, const void *r2)
- {
-       const struct ref_update * const *u1 = r1;
-       const struct ref_update * const *u2 = r2;
-       return strcmp((*u1)->refname, (*u2)->refname);
- }
- static int ref_update_reject_duplicates(struct ref_update **updates, int n,
+ static int ref_update_reject_duplicates(struct string_list *refnames,
                                        struct strbuf *err)
  {
-       int i;
+       int i, n = refnames->nr;
  
        assert(err);
  
        for (i = 1; i < n; i++)
-               if (!strcmp(updates[i - 1]->refname, updates[i]->refname)) {
+               if (!strcmp(refnames->items[i - 1].string, refnames->items[i].string)) {
                        strbuf_addf(err,
                                    "Multiple updates for ref '%s' not allowed.",
-                                   updates[i]->refname);
+                                   refnames->items[i].string);
                        return 1;
                }
        return 0;
@@@ -3778,6 -3801,7 +3852,7 @@@ int ref_transaction_commit(struct ref_t
        struct ref_update **updates = transaction->updates;
        struct string_list refs_to_delete = STRING_LIST_INIT_NODUP;
        struct string_list_item *ref_to_delete;
+       struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
  
        assert(err);
  
                return 0;
        }
  
-       /* Copy, sort, and reject duplicate refs */
-       qsort(updates, n, sizeof(*updates), ref_update_compare);
-       if (ref_update_reject_duplicates(updates, n, err)) {
+       /* Fail if a refname appears more than once in the transaction: */
+       for (i = 0; i < n; i++)
+               string_list_append(&affected_refnames, updates[i]->refname);
+       string_list_sort(&affected_refnames);
+       if (ref_update_reject_duplicates(&affected_refnames, err)) {
                ret = TRANSACTION_GENERIC_ERROR;
                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];
 -              unsigned int flags = update->flags;
  
 -              if ((flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1))
 -                      flags |= REF_DELETING;
 +              if ((update->flags & REF_HAVE_NEW) &&
 +                  is_null_sha1(update->new_sha1))
 +                      update->flags |= REF_DELETING;
                update->lock = lock_ref_sha1_basic(
                                update->refname,
                                ((update->flags & REF_HAVE_OLD) ?
                                 update->old_sha1 : NULL),
-                               NULL,
+                               &affected_refnames, NULL,
 -                              flags,
 +                              update->flags,
-                               &update->type);
+                               &update->type,
+                               err);
                if (!update->lock) {
+                       char *reason;
                        ret = (errno == ENOTDIR)
                                ? TRANSACTION_NAME_CONFLICT
                                : TRANSACTION_GENERIC_ERROR;
-                       strbuf_addf(err, "Cannot lock the ref '%s'.",
-                                   update->refname);
+                       reason = strbuf_detach(err, NULL);
+                       strbuf_addf(err, "Cannot lock ref '%s': %s",
+                                   update->refname, reason);
+                       free(reason);
                        goto cleanup;
                }
 -      }
 -
 -      /* Perform updates first so live commits remain referenced */
 -      for (i = 0; i < n; i++) {
 -              struct ref_update *update = updates[i];
 -              int flags = update->flags;
 -
 -              if ((flags & REF_HAVE_NEW) && !is_null_sha1(update->new_sha1)) {
 +              if ((update->flags & REF_HAVE_NEW) &&
 +                  !(update->flags & REF_DELETING)) {
                        int overwriting_symref = ((update->type & REF_ISSYMREF) &&
                                                  (update->flags & REF_NODEREF));
  
 -                      if (!overwriting_symref
 -                          && !hashcmp(update->lock->old_sha1, update->new_sha1)) {
 +                      if (!overwriting_symref &&
 +                          !hashcmp(update->lock->old_sha1, update->new_sha1)) {
                                /*
                                 * The reference already has the desired
                                 * value, so we don't need to write it.
                                 */
 -                              unlock_ref(update->lock);
 +                      } else 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;
 +                      } else {
 +                              update->flags |= REF_NEEDS_COMMIT;
 +                      }
 +              }
 +              if (!(update->flags & REF_NEEDS_COMMIT)) {
 +                      /*
 +                       * 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 (update->flags & REF_NEEDS_COMMIT) {
 +                      if (commit_ref_update(update->lock,
 +                                            update->new_sha1, update->msg)) {
 +                              /* freed by commit_ref_update(): */
                                update->lock = NULL;
 -                      } else if (write_ref_sha1(update->lock, update->new_sha1,
 -                                                update->msg)) {
 -                              update->lock = NULL; /* freed by write_ref_sha1 */
                                strbuf_addf(err, "Cannot update the ref '%s'.",
                                            update->refname);
                                ret = TRANSACTION_GENERIC_ERROR;
                                goto cleanup;
                        } else {
 -                              /* freed by write_ref_sha1(): */
 +                              /* freed by commit_ref_update(): */
                                update->lock = NULL;
                        }
                }
        /* Perform deletes now that updates are safely completed */
        for (i = 0; i < n; i++) {
                struct ref_update *update = updates[i];
 -              int flags = update->flags;
  
 -              if ((flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1)) {
 +              if (update->flags & REF_DELETING) {
                        if (delete_ref_loose(update->lock, update->type, err)) {
                                ret = TRANSACTION_GENERIC_ERROR;
                                goto cleanup;
                        }
  
 -                      if (!(flags & REF_ISPRUNING))
 +                      if (!(update->flags & REF_ISPRUNING))
                                string_list_append(&refs_to_delete,
                                                   update->lock->ref_name);
                }
@@@ -3913,6 -3914,7 +3995,7 @@@ cleanup
                if (updates[i]->lock)
                        unlock_ref(updates[i]->lock);
        string_list_clear(&refs_to_delete, 0);
+       string_list_clear(&affected_refnames, 0);
        return ret;
  }
  
@@@ -4102,6 -4104,7 +4185,7 @@@ int reflog_expire(const char *refname, 
        char *log_file;
        int status = 0;
        int type;
+       struct strbuf err = STRBUF_INIT;
  
        memset(&cb, 0, sizeof(cb));
        cb.flags = flags;
         * reference itself, plus we might need to update the
         * reference if --updateref was specified:
         */
-       lock = lock_ref_sha1_basic(refname, sha1, NULL, 0, &type);
-       if (!lock)
-               return error("cannot lock ref '%s'", refname);
+       lock = lock_ref_sha1_basic(refname, sha1, NULL, NULL, 0, &type, &err);
+       if (!lock) {
+               error("cannot lock ref '%s': %s", refname, err.buf);
+               strbuf_release(&err);
+               return -1;
+       }
        if (!reflog_exists(refname)) {
                unlock_ref(lock);
                return 0;
                        status |= error("couldn't write %s: %s", log_file,
                                        strerror(errno));
                } else if (update &&
 -                      (write_in_full(lock->lock_fd,
 +                         (write_in_full(lock->lk->fd,
                                sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
 -                       write_str_in_full(lock->lock_fd, "\n") != 1 ||
 +                       write_str_in_full(lock->lk->fd, "\n") != 1 ||
                         close_ref(lock) < 0)) {
                        status |= error("couldn't write %s",
                                        lock->lk->filename.buf);
diff --combined t/t1400-update-ref.sh
index 636d3a167c4aa17bbb8f8b58d6a66142d90d1af2,86fa46856c47aecfc9901039cc868253b896156f..ba89f4c00959112b2cfc0efaff94f3447df32357
@@@ -519,7 -519,7 +519,7 @@@ test_expect_success 'stdin create ref w
  test_expect_success 'stdin update ref fails with wrong old value' '
        echo "update $c $m $m~1" >stdin &&
        test_must_fail git update-ref --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$c'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$c'"'"'" err &&
        test_must_fail git rev-parse --verify -q $c
  '
  
@@@ -555,7 -555,7 +555,7 @@@ test_expect_success 'stdin update ref w
  test_expect_success 'stdin delete ref fails with wrong old value' '
        echo "delete $a $m~1" >stdin &&
        test_must_fail git update-ref --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$a'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$a'"'"'" err &&
        git rev-parse $m >expect &&
        git rev-parse $a >actual &&
        test_cmp expect actual
@@@ -688,7 -688,7 +688,7 @@@ test_expect_success 'stdin update refs 
        update $c  ''
        EOF
        test_must_fail git update-ref --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$c'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$c'"'"'" err &&
        git rev-parse $m >expect &&
        git rev-parse $a >actual &&
        test_cmp expect actual &&
@@@ -883,7 -883,7 +883,7 @@@ test_expect_success 'stdin -z create re
  test_expect_success 'stdin -z update ref fails with wrong old value' '
        printf $F "update $c" "$m" "$m~1" >stdin &&
        test_must_fail git update-ref -z --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$c'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$c'"'"'" err &&
        test_must_fail git rev-parse --verify -q $c
  '
  
@@@ -899,7 -899,7 +899,7 @@@ test_expect_success 'stdin -z create re
        git rev-parse "$c" >expect &&
        printf $F "create $c" "$m~1" >stdin &&
        test_must_fail git update-ref -z --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$c'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$c'"'"'" err &&
        git rev-parse "$c" >actual &&
        test_cmp expect actual
  '
@@@ -930,7 -930,7 +930,7 @@@ test_expect_success 'stdin -z update re
  test_expect_success 'stdin -z delete ref fails with wrong old value' '
        printf $F "delete $a" "$m~1" >stdin &&
        test_must_fail git update-ref -z --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$a'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$a'"'"'" err &&
        git rev-parse $m >expect &&
        git rev-parse $a >actual &&
        test_cmp expect actual
@@@ -1045,7 -1045,7 +1045,7 @@@ test_expect_success 'stdin -z update re
        git update-ref $c $m &&
        printf $F "update $a" "$m" "$m" "update $b" "$m" "$m" "update $c" "$m" "$Z" >stdin &&
        test_must_fail git update-ref -z --stdin <stdin 2>err &&
-       grep "fatal: Cannot lock the ref '"'"'$c'"'"'" err &&
+       grep "fatal: Cannot lock ref '"'"'$c'"'"'" err &&
        git rev-parse $m >expect &&
        git rev-parse $a >actual &&
        test_cmp expect actual &&
@@@ -1065,32 -1065,4 +1065,32 @@@ test_expect_success 'stdin -z delete re
        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