From eea63587e692fa1dc44c2d96c0a53788835fac7d Mon Sep 17 00:00:00 2001
From: Liu Hua <weldonliu@tencent.com>
Date: Thu, 2 Sep 2021 11:10:41 +0800
Subject: [PATCH] namespaces: add helpers to switch/restore mnt ns

When restoring mnt, we should restore current work directory.

Signed-off-by: Liu Hua <weldonliu@tencent.com>
---
 criu/include/namespaces.h |  2 ++
 criu/namespaces.c         | 45 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/criu/include/namespaces.h b/criu/include/namespaces.h
index ddf0dbabb..034605917 100644
--- a/criu/include/namespaces.h
+++ b/criu/include/namespaces.h
@@ -165,8 +165,10 @@ extern int prepare_namespace(struct pstree_item *item, unsigned long clone_flags
 extern int prepare_userns_creds(void);
 
 extern int switch_ns(int pid, struct ns_desc *nd, int *rst);
+extern int switch_mnt_ns(int pid, int *rst, int *cwd_fd);
 extern int switch_ns_by_fd(int nsfd, struct ns_desc *nd, int *rst);
 extern int restore_ns(int rst, struct ns_desc *nd);
+extern int restore_mnt_ns(int rst, int *cwd_fd);
 
 extern int dump_task_ns_ids(struct pstree_item *);
 extern int predump_task_ns_ids(struct pstree_item *);
diff --git a/criu/namespaces.c b/criu/namespaces.c
index 92e0ed31a..7fa58682b 100644
--- a/criu/namespaces.c
+++ b/criu/namespaces.c
@@ -282,6 +282,51 @@ int restore_ns(int rst, struct ns_desc *nd)
 	return ret;
 }
 
+int switch_mnt_ns(int pid, int *rst, int *cwd_fd)
+{
+	int ret;
+	int fd;
+
+	if (!cwd_fd)
+		return switch_ns(pid, &mnt_ns_desc, rst);
+
+	fd = open(".", O_PATH);
+	if (fd < 0) {
+		pr_perror("unable to open current directory");
+		return fd;
+	}
+
+	ret = switch_ns(pid, &mnt_ns_desc, rst);
+	if (ret < 0) {
+		close(fd);
+		return ret;
+	}
+
+	*cwd_fd = fd;
+	return 0;
+}
+
+int restore_mnt_ns(int rst, int *cwd_fd)
+{
+	int ret = -1;
+
+	ret = restore_ns(rst, &mnt_ns_desc);
+	if (ret < 0)
+		goto err_restore;
+
+	if (cwd_fd) {
+		ret = fchdir(*cwd_fd);
+		if (ret)
+			pr_perror("unable to restore current directory");
+	}
+
+err_restore:
+	if (cwd_fd)
+		close_safe(cwd_fd);
+
+	return ret;
+}
+
 struct ns_id *ns_ids = NULL;
 static unsigned int ns_next_id = 1;
 unsigned long root_ns_mask = 0;