ctdb-scripts: Provide a gstack function if gstack is not available

gstack isn't widely available, so provide a simple function that does
the same thing if it gstack can't be found.

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Wed Jul 11 14:47:21 CEST 2018 on sn-devel-144

ctdb/config/debug_locks.sh

@@ -12,6 +12,19 @@
 
 . "${CTDB_BASE}/functions"
 
+# type is at least mentioned in POSIX and more is portable than which(1)
+# shellcheck disable=SC2039
+if ! type gstack >/dev/null 2>&1 ; then
+	gstack ()
+	{
+		_pid="$1"
+
+		gdb -batch --quiet -nx "/proc/${_pid}/exe" "$_pid" \
+		    -ex "thread apply all bt" 2>/dev/null |
+			grep '^\(#\|Thread \)'
+	}
+fi
+
 # Load/cache database options from configuration file
 ctdb_get_db_options
 
@@ -72,7 +85,6 @@ ctdb_get_db_options
 		cat "/proc/${pid}/stack"
 	    else
 		gstack "$pid"
-		# gcore -o /var/log/core-deadlock-ctdb $pid
 	    fi
 	done
     fi