restore: get real pid for each task (v2)

For the root task the clone syscall returns the pid in criu's pidns,
but for other processes the clone syscall returns PID in the restored
namespace.

The /proc/self link contains the PID value of the current process, so if
we want to determing the PID in a criu's pidns, we should use criu's
/proc.

v2: readlink() does not append a null byte to buf, so we must do that
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-restore.c

@@ -953,7 +953,7 @@ static inline int fork_with_pid(struct pstree_item *item)
 	if (ret < 0)
 		pr_perror("Can't fork for %d", pid);
 
-	if (ca.clone_flags & CLONE_NEWPID)
+	if (item == root_item)
 		item->pid.real = ret;
 
 	if (opts.pidfile && root_item == item) {
@@ -1149,6 +1149,27 @@ static int restore_task_with_children(void *_arg)
 
 	current = ca->item;
 
+	if (current != root_item) {
+		char buf[PATH_MAX];
+		int fd;
+
+		/* Determine PID in CRIU's namespace */
+		fd = get_service_fd(CR_PROC_FD_OFF);
+		if (fd < 0)
+			exit(1);
+
+		ret = readlinkat(fd, "self", buf, sizeof(buf) - 1);
+		if (ret < 0) {
+			pr_perror("Unable to read the /proc/self link");
+			exit(1);
+		}
+		buf[ret] = '\0';
+
+		current->pid.real = atoi(buf);
+		pr_debug("PID: real %d virt %d\n",
+				current->pid.real, current->pid.virt);
+	}
+
 	if ( !(ca->clone_flags & CLONE_FILES))
 		close_safe(&ca->fd);
 
@@ -1293,9 +1314,20 @@ static int restore_switch_stage(int next_stage)
 
 static int restore_root_task(struct pstree_item *init)
 {
-	int ret;
+	int ret, fd;
 	struct sigaction act, old_act;
 
+	fd = open("/proc", O_DIRECTORY | O_RDONLY);
+	if (fd < 0) {
+		pr_perror("Unable to open /proc");
+		return -1;
+	}
+
+	ret = install_service_fd(CR_PROC_FD_OFF, fd);
+	close(fd);
+	if (ret < 0)
+		return -1;
+
 	ret = sigaction(SIGCHLD, NULL, &act);
 	if (ret < 0) {
 		pr_perror("sigaction() failed");

files.c

@@ -933,6 +933,7 @@ int prepare_fds(struct pstree_item *me)
 	if (me->rst->fdt)
 		futex_inc_and_wake(&me->rst->fdt->fdt_lock);
 out:
+	close_service_fd(CR_PROC_FD_OFF);
 	tty_fini_fds();
 	return ret;
 }

include/crtools.h

@@ -54,10 +54,11 @@ enum sfd_type {
 	LOG_FD_OFF,
 	LOG_DIR_FD_OFF,
 	IMG_FD_OFF,
-	PROC_FD_OFF,
+	PROC_FD_OFF,	/* /proc in the restored pidns */
 	CTL_TTY_OFF,
 	SELF_STDIN_OFF,
 	PARENT_FD_OFF,
+	CR_PROC_FD_OFF, /* /proc in criu's pidns */
 
 	SERVICE_FD_MAX
 };