Set FD_CLOEXEC on the pidfile fd, so that tapdisk does not get it.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

tools/blktap/drivers/blktapctrl.c

@@ -629,6 +629,7 @@ static void write_pidfile(long pid)
 	char buf[100];
 	int len;
 	int fd;
+	int flags;
 
 	fd = open(PIDFILE, O_RDWR | O_CREAT, 0600);
 	if (fd == -1) {
@@ -640,6 +641,18 @@ static void write_pidfile(long pid)
 	if (lockf(fd, F_TLOCK, 0) == -1)
 		exit(0);
 
+	/* Set FD_CLOEXEC, so that tapdisk doesn't get this file
+	   descriptor. */
+	if ((flags = fcntl(fd, F_GETFD)) == -1) {
+		DPRINTF("F_GETFD failed (%d)\n", errno);
+		exit(1);
+	}
+	flags |= FD_CLOEXEC;
+	if (fcntl(fd, F_SETFD, flags) == -1) {
+		DPRINTF("F_SETFD failed (%d)\n", errno);
+		exit(1);
+	}
+
 	len = sprintf(buf, "%ld\n", pid);
 	if (write(fd, buf, len) != len) {
 		DPRINTF("Writing pid file failed (%d)\n", errno);