   (let ((str (git-call-process-env-string nil "symbolic-ref" ref)))
     (and str (car (split-string str "\n")))))
 
-(defun git-update-ref (ref val &optional oldval)
+(defun git-update-ref (ref newval &optional oldval reason)
   "Update a reference by calling git-update-ref."
-  (apply #'git-call-process-env nil nil "update-ref" ref val (if oldval (list oldval))))
+  (let ((args (and oldval (list oldval))))
+    (push newval args)
+    (push ref args)
+    (when reason
+     (push reason args)
+     (push "-m" args))
+    (eq 0 (apply #'git-call-process-env nil nil "update-ref" args))))
 
 (defun git-read-tree (tree &optional index-file)
   "Read a tree into the index file."

  "Call git-commit-tree with buffer as input and return the resulting commit SHA1."
  (let ((author-name (git-get-committer-name))
        (author-email (git-get-committer-email))
        author-date log-start log-end args coding-system-for-write)
    (when head
      (push "-p" args)
      (push head args))
    (with-current-buffer buffer

            (goto-char (point-min))
            (while (re-search-forward "^Parent: +\\([0-9a-f]+\\)" nil t)
              (unless (string-equal head (match-string 1))
                (setq subject "commit (merge): ")
                (push "-p" args)
                (push (match-string 1) args))))
        (setq log-start (point-min)))
      (setq log-end (point-max))
      (goto-char log-start)
      (when (re-search-forward ".*$" nil t)
        (setq subject (concat subject (match-string 0))))
      (setq coding-system-for-write buffer-file-coding-system))
    (let ((commit
           (git-get-string-sha1
            (with-output-to-string
              (with-current-buffer standard-output
                (let ((env `(("GIT_AUTHOR_NAME" . ,author-name)
                             ("GIT_AUTHOR_EMAIL" . ,author-email)
                             ("GIT_COMMITTER_NAME" . ,(git-get-committer-name))
                             ("GIT_COMMITTER_EMAIL" . ,(git-get-committer-email)))))
                  (when author-date (push `("GIT_AUTHOR_DATE" . ,author-date) env))
                  (apply #'git-run-command-region
                         buffer log-start log-end env
                         "commit-tree" tree (nreverse args))))))))
      (and (git-update-ref "HEAD" commit head subject)
           commit))))

(defun git-empty-db-p ()
  "Check if the git db is empty (no commit done yet)."
