tools/xenstore: switch barf[_perror]() to use syslog()

When xenstored crashes due to an unrecoverable condition it is calling
either barf() or barf_perror() to issue a message and then exit().

Make sure the message is visible somewhere by using syslog()
additionally to xprintf(), as the latter will be visible only with
tracing active.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Julien Grall <jgrall@amazon.com>

tools/xenstore/utils.c

@@ -3,6 +3,7 @@
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
+#include <syslog.h>
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
@@ -35,6 +36,7 @@ void barf(const char *fmt, ...)
 	va_end(arglist);
 
  	if (bytes >= 0) {
+		syslog(LOG_CRIT, "%s\n", str);
 		xprintf("%s\n", str);
 		free(str);
 	}
@@ -54,6 +56,7 @@ void barf_perror(const char *fmt, ...)
 	va_end(arglist);
 
  	if (bytes >= 0) {
+		syslog(LOG_CRIT, "%s: %s\n", str, strerror(err));
 		xprintf("%s: %s\n", str, strerror(err));
 		free(str);
 	}