References: bsc#1178736

Allow restart of xenwatchdogd in case it terminated unexpectetly.
Index: xen-4.19.0-testing/tools/misc/xenwatchdogd.c
===================================================================
--- xen-4.19.0-testing.orig/tools/misc/xenwatchdogd.c
+++ xen-4.19.0-testing/tools/misc/xenwatchdogd.c
@@ -21,6 +21,8 @@
 #include <stdio.h>
 #include <stdbool.h>
 #include <getopt.h>
+#include <libgen.h>
+#include <syslog.h>
 
 #define WDOG_MIN_TIMEOUT 2
 #define WDOG_MIN_SLEEP 1
@@ -29,9 +31,11 @@
 static xc_interface *h;
 static volatile bool safeexit = false;
 static volatile bool done = false;
+static const char id_file[] = "/run/xenwatchdog_id.txt";
 
-static void daemonize(void)
+static void daemonize(const char *str)
 {
+    const char *err_str = "";
     switch (fork()) {
     case -1:
 	err(EXIT_FAILURE, "fork");
@@ -40,7 +44,9 @@ static void daemonize(void)
     default:
 	exit(EXIT_SUCCESS);
     }
-    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(EXIT_FAILURE, "setsid");
     if (chdir("/") < 0)
@@ -51,6 +57,10 @@ static void daemonize(void)
         err(EXIT_FAILURE, "reopen stdout");
     if(freopen("/dev/null", "w", stderr) == NULL)
         err(EXIT_FAILURE, "reopen stderr");
+    return;
+out:
+    syslog(LOG_ERR, "%s: %m", err_str);
+    exit(1);
 }
 
 static void catch_exit(int sig)
@@ -62,6 +72,7 @@ static void catch_usr1(int sig)
 {
     safeexit = true;
     done = true;
+    unlink(id_file);
 }
 
 static void __attribute__((noreturn)) usage(int exit_code)
@@ -98,10 +109,12 @@ static int parse_secs(const char *arg, c
 
 int main(int argc, char **argv)
 {
+    FILE *f;
     int id;
     int t, s;
     int ret;
     bool daemon = true;
+    const char *err_str = "";
 
     for ( ;; )
     {
@@ -160,7 +173,7 @@ int main(int argc, char **argv)
 	s = t / 2;
 
     if (daemon)
-	daemonize();
+	daemonize(basename(argv[0]));
 
     h = xc_interface_open(NULL, NULL, 0);
     if (h == NULL)
@@ -177,9 +190,25 @@ int main(int argc, char **argv)
     if (signal(SIGUSR1, &catch_usr1) == SIG_ERR)
 	err(EXIT_FAILURE, "signal");
 
-    id = xc_watchdog(h, 0, t);
-    if (id <= 0)
-        err(EXIT_FAILURE, "xc_watchdog setup");
+    f = fopen(id_file, "r");
+    if (f) {
+        if (fscanf(f, "%d", &id) != 1)
+            id = -1;
+        if (id <= 0)
+            err(EXIT_FAILURE, "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(EXIT_FAILURE, "xc_watchdog setup");
+        f = fopen(id_file, "w");
+        if (f) {
+            fprintf(f, "%d\n", id);
+            fclose(f);
+        }
+    }
 
     while (!done) {
         sleep(s);
@@ -191,4 +220,8 @@ int main(int argc, char **argv)
     // Zero seconds timeout will disarm the watchdog timer
     xc_watchdog(h, id, safeexit ? 0 : WDOG_EXIT_TIMEOUT);
     return 0;
+
+out:
+    syslog(LOG_ERR, "%s: %m", err_str);
+    exit(EXIT_FAILURE);
 }