net/tramp.el (tramp-ssh-controlmaster-options): Use "%C"

Fixes: debbugs:19702

* net/tramp.el (tramp-ssh-controlmaster-options): Use "%C" for
ControlPath if possible.

2 files changed, 21 insertions, 8 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index cc42bcecc9c..8ef533e1aa6 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-02  Michael Albinus  <michael.albinus@gmx.de>
+
+        * net/tramp.el (tramp-ssh-controlmaster-options): Use "%C" for
+        ControlPath if possible.  (Bug#19702)
+
 2015-02-02  Glenn Morris  <rgm@gnu.org>
 
         * emacs-lisp/authors.el (authors-obsolete-files-regexps)
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 3afb487ec3d..c442806b90f 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -311,17 +311,25 @@ useful only in combination with `tramp-default-proxies-alist'.")
   (let ((result "")
         (case-fold-search t))
     (ignore-errors
-      (with-temp-buffer
-        (call-process "ssh" nil t nil "-o" "ControlMaster")
-        (goto-char (point-min))
-        (when (search-forward-regexp "missing.+argument" nil t)
-          (setq result "-o ControlPath=%t.%%r@%%h:%%p -o ControlMaster=auto")))
-      (unless (zerop (length result))
+      (when (executable-find "ssh")
         (with-temp-buffer
-          (call-process "ssh" nil t nil "-o" "ControlPersist")
+          (call-process "ssh" nil t nil "-o" "ControlMaster")
           (goto-char (point-min))
           (when (search-forward-regexp "missing.+argument" nil t)
-            (setq result (concat result " -o ControlPersist=no"))))))
+            (setq result "-o ControlMaster=auto")))
+        (unless (zerop (length result))
+          (with-temp-buffer
+            (call-process
+             "ssh" nil t nil "-o" "ControlPath=%C" "host.does.not.exist")
+            (goto-char (point-min))
+            (if (search-forward-regexp "unknown.+key" nil t)
+                (setq result (concat result " -o ControlPath=%t.%%r@%%h:%%p"))
+              (setq result (concat result " -o ControlPath=%t.%%C"))))
+          (with-temp-buffer
+            (call-process "ssh" nil t nil "-o" "ControlPersist")
+            (goto-char (point-min))
+            (when (search-forward-regexp "missing.+argument" nil t)
+              (setq result (concat result " -o ControlPersist=no")))))))
     result)
     "Call ssh to detect whether it supports the Control* arguments.
 Return a string to be used in `tramp-methods'.")