page-xfer: write pidfile from a process which starts a service

When a process, which starts a service, exits, we know that we can
connect to the page server and we expect to find pidfile.

If we create pidfile from a page server process, we have a race window.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

page-xfer.c

@@ -4,6 +4,8 @@
 #include <linux/falloc.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <sys/types.h>
+#include <sys/wait.h>
 
 #include "cr_options.h"
 #include "servicefd.h"
@@ -309,17 +311,20 @@ no_server:
 			pr_perror("Can't run in the background");
 			goto out;
 		}
-		if (ret > 0) /* parent task, daemon started */
-			return ret;
-	}
-
+		if (ret > 0) { /* parent task, daemon started */
 			if (opts.pidfile) {
-		if (write_pidfile(getpid()) == -1) {
+				if (write_pidfile(ret) == -1) {
 					pr_perror("Can't write pidfile");
+					kill(ret, SIGKILL);
+					waitpid(ret, NULL, 0);
 					return -1;
 				}
 			}
 
+			return ret;
+		}
+	}
+
 	if (sk >= 0) {
 		ret = ask = accept(sk, (struct sockaddr *)&caddr, &clen);
 		if (ask < 0)

test/zdtm.sh

@@ -573,8 +573,8 @@ EOF
 		[ -n "$DUMP_ONLY" ] && dump_only=1
 
 		if [ $PAGE_SERVER -eq 1 ]; then
-			$CRIU page-server -D $ddump -o page_server.log -v4 --port $PS_PORT $ps_args --daemon || return 1
-			ps_pid=`lsof -s TCP:LISTEN -i :$PS_PORT -t`
+			$CRIU page-server -D $ddump -o page_server.log -v4 --port $PS_PORT $ps_args --daemon --pidfile $ddump/page-server.pid || return 1
+			ps_pid=`cat $ddump/page-server.pid`
 			ps -p "$ps_pid" -o cmd h | grep -q page-server || {
 				echo "Unable to determing PID of page-server"
 				return 1