From: Patrick Donnelly <pdonnell@redhat.com>
Date: Thu, 6 Oct 2016 22:54:44 +0000 (-0400)
Subject: mds: respawn using /proc/self/exe
X-Git-Tag: v10.2.6~36^2~5^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F11873%2Fhead;p=ceph.git

mds: respawn using /proc/self/exe

This allows the MDS to respawn using the same executable file even if it
has since been deleted (on Linux). Otherwise, the execv fails because
the readlink returns "/path/to/deleted (deleted)". (There is no path to
the old executable.)

Fixes: http://tracker.ceph.com/issues/17531

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>
(cherry picked from commit 66a122025f6cf023cf7b2f3d8fbe4964fb7568a7)
---

diff --git a/src/mds/MDSDaemon.cc b/src/mds/MDSDaemon.cc
index 0482477b7cc3..9d2e60300214 100644
--- a/src/mds/MDSDaemon.cc
+++ b/src/mds/MDSDaemon.cc
@@ -1114,12 +1114,12 @@ void MDSDaemon::respawn()
   }
   new_argv[orig_argc] = NULL;
 
-  /* Determine the path to our executable, try to read
-   * linux-specific /proc/ path first */
-  char exe_path[PATH_MAX];
-  ssize_t exe_path_bytes = readlink("/proc/self/exe", exe_path,
-				    sizeof(exe_path) - 1);
-  if (exe_path_bytes < 0) {
+  /* Determine the path to our executable, test if Linux /proc/self/exe exists.
+   * This allows us to exec the same executable even if it has since been
+   * unlinked.
+   */
+  char exe_path[PATH_MAX] = "";
+  if (readlink("/proc/self/exe", exe_path, PATH_MAX-1) == -1) {
     /* Print CWD for the user's interest */
     char buf[PATH_MAX];
     char *cwd = getcwd(buf, sizeof(buf));
@@ -1127,9 +1127,10 @@ void MDSDaemon::respawn()
     dout(1) << " cwd " << cwd << dendl;
 
     /* Fall back to a best-effort: just running in our CWD */
-    strncpy(exe_path, orig_argv[0], sizeof(exe_path) - 1);
+    strncpy(exe_path, orig_argv[0], PATH_MAX-1);
   } else {
-    exe_path[exe_path_bytes] = '\0';
+    dout(1) << "respawning with exe " << exe_path << dendl;
+    strcpy(exe_path, "/proc/self/exe");
   }
 
   dout(1) << " exe_path " << exe_path << dendl;