[CRIU] [PATCH 02/15] restore: get real pid for each task (v2)

[Andrey Vagin]

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 at openvz.org>
---
 cr-restore.c      | 36 ++++++++++++++++++++++++++++++++++--
 files.c           |  1 +
 include/crtools.h |  3 ++-
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/cr-restore.c b/cr-restore.c
index c35ec7f..71aae4d 100644
--- a/cr-restore.c
+++ b/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");
diff --git a/files.c b/files.c
index 8193d59..e194a22 100644
--- a/files.c
+++ b/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;
 }
diff --git a/include/crtools.h b/include/crtools.h
index f15cbc6..a574b46 100644
--- a/include/crtools.h
+++ b/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
 };
-- 
1.8.3.1