References: bsc#1178736

Allow restart of xenwatchdogd in case it terminated unexpectetly.
Index: xen-4.14.0-testing/tools/misc/xenwatchdogd.c
===================================================================
--- xen-4.14.0-testing.orig/tools/misc/xenwatchdogd.c
+++ xen-4.14.0-testing/tools/misc/xenwatchdogd.c
@@ -9,12 +9,16 @@
 #include <unistd.h>
 #include <signal.h>
 #include <stdio.h>
+#include <libgen.h>
+#include <syslog.h>
 
 xc_interface *h;
 int id = 0;
+static const char id_file[] = "/run/xenwatchdog_id.txt";
 
-void daemonize(void)
+static void daemonize(const char *str)
 {
+    const char *err_str = "";
     switch (fork()) {
     case -1:
 	err(1, "fork");
@@ -23,7 +27,9 @@ void daemonize(void)
     default:
 	exit(0);
     }
-    umask(0);
+#define err(x,s) do { err_str = (s); goto out; } while (0)
+    openlog(str, LOG_CONS, LOG_DAEMON);
+    umask(~(S_IRUSR|S_IWUSR));
     if (setsid() < 0)
 	err(1, "setsid");
     if (chdir("/") < 0)
@@ -34,6 +40,10 @@ void daemonize(void)
         err(1, "reopen stdout");
     if(freopen("/dev/null", "w", stderr) == NULL)
         err(1, "reopen stderr");
+    return;
+out:
+    syslog(LOG_ERR, "%s: %m", err_str);
+    exit(1);
 }
 
 void catch_exit(int sig)
@@ -47,18 +57,21 @@ void catch_usr1(int sig)
 {
     if (id)
         xc_watchdog(h, id, 0);
+    unlink(id_file);
     exit(0);
 }
 
 int main(int argc, char **argv)
 {
+    FILE *f;
     int t, s;
     int ret;
+    const char *err_str = "";
 
     if (argc < 2)
 	errx(1, "usage: %s <timeout> <sleep>", argv[0]);
 
-    daemonize();
+    daemonize(basename(argv[0]));
 
     h = xc_interface_open(NULL, NULL, 0);
     if (h == NULL)
@@ -86,9 +99,25 @@ int main(int argc, char **argv)
     if (signal(SIGUSR1, &catch_usr1) == SIG_ERR)
 	err(1, "signal");
 
-    id = xc_watchdog(h, 0, t);
-    if (id <= 0)
-        err(1, "xc_watchdog setup");
+    f = fopen(id_file, "r");
+    if (f) {
+        if (fscanf(f, "%d", &id) != 1)
+            id = -1;
+        if (id <= 0)
+            err(1, "xc_watchdog setup");
+        syslog(LOG_INFO, "reusing id %d", id);
+        fclose(f);
+    } else {
+        id = xc_watchdog(h, 0, t);
+        syslog(LOG_INFO, "obtained id %d", id);
+        if (id <= 0)
+            err(1, "xc_watchdog setup");
+        f = fopen(id_file, "w");
+        if (f) {
+            fprintf(f, "%d\n", id);
+            fclose(f);
+        }
+    }
 
     for (;;) {
         sleep(s);
@@ -96,4 +125,8 @@ int main(int argc, char **argv)
         if (ret != 0)
             err(1, "xc_watchdog");
     }
+
+out:
+    syslog(LOG_ERR, "%s: %m", err_str);
+    exit(1);
 }