mount: save local mount point paths on restore

On restore we add a temporary root to a mount point path. It's convinient
for restoring mount namespaces, but real paths are used for restoring
link-remap files.

v2: replace the offset field on a char * field
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/proc_parse.h

@@ -114,8 +114,10 @@ struct mount_info {
 	 * On restore mountpoint is prepended with so called ns
 	 * root path -- it's a place in fs where the namespace
 	 * mount tree is constructed. Check mnt_roots for details.
+	 * The ns_mountpoint contains path w/o this prefix.
 	 */
 	char		*mountpoint;
+	char		*ns_mountpoint;
 	unsigned	flags;
 	int		master_id;
 	int		shared_id;

mount.c

@@ -1669,6 +1669,7 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
 		pm->mountpoint = xmalloc(len);
 		if (!pm->mountpoint)
 			goto err;
+		pm->ns_mountpoint = pm->mountpoint + root_len;
 		/*
 		 * For bind-mounts we would also fix the root here
 		 * too, but bind-mounts restore merges mountpoint