xen/suspend_evtchn_lock.patch

Fix problems that suspend eventchannel lock file might be obselete for some reason
like segment fault or other abnormal exit, and once obselete lock file exists,
it might affact latter save process.
Have discussed with upstream, for some reason not accepted. 
http://xen.1045712.n5.nabble.com/Re-PATCH-improve-suspend-evtchn-lock-processing-td3395229.html

Signed-off-by: Chunyan Liu <cyliu@suse.com>

Index: xen-4.6.0-testing/tools/libxc/xc_suspend.c
===================================================================
--- xen-4.6.0-testing.orig/tools/libxc/xc_suspend.c
+++ xen-4.6.0-testing/tools/libxc/xc_suspend.c
@@ -18,6 +18,10 @@
 
 #include "xc_private.h"
 #include "xenguest.h"
+#include <signal.h>
+#ifdef __MINIOS__
+extern int kill (__pid_t __pid, int __sig);
+#endif
 
 #define SUSPEND_LOCK_FILE    XEN_RUN_DIR "/suspend-evtchn-%d.lock"
 
@@ -33,6 +37,37 @@
 
 #define SUSPEND_FILE_BUFLEN (sizeof(SUSPEND_LOCK_FILE) + 10)
 
+/* cleanup obsolete suspend lock file which is unlinked for any reason,
+so that current process can get lock */
+static void clean_obsolete_lock(int domid)
+{
+    int fd, pid, n;
+    char buf[128];
+    char suspend_file[256];
+
+    snprintf(suspend_file, sizeof(suspend_file), "%s_%d_lock.d",
+        SUSPEND_LOCK_FILE, domid);
+    fd = open(suspend_file, O_RDWR);
+
+    if (fd < 0)
+        return;
+
+    n = read(fd, buf, 127);
+
+    close(fd);
+
+    if (n > 0)
+    {
+        sscanf(buf, "%d", &pid);
+        /* pid does not exist, this lock file is obsolete, just delete it */
+        if ( kill(pid,0) )
+        {
+            unlink(suspend_file);
+            return;
+        }
+    }
+}
+
 static void get_suspend_file(char buf[], int domid)
 {
     snprintf(buf, SUSPEND_FILE_BUFLEN, SUSPEND_LOCK_FILE, domid);
@@ -46,6 +81,7 @@ static int lock_suspend_event(xc_interfa
     struct flock fl;
 
     get_suspend_file(suspend_file, domid);
+    clean_obsolete_lock(domid);
 
     *lockfd = -1;
 
@@ -95,6 +131,8 @@ static int lock_suspend_event(xc_interfa
     if (fd >= 0)
         close(fd);
 
+    unlink(suspend_file);
+
     return -1;
 }