mount: save mount tree for each namespace

We are going to support nested mount namespaces and each NS has own
tree. The mount tree is used for checking that a file is reachable.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/mount.h

@@ -10,7 +10,8 @@ extern int collect_mount_info(pid_t pid);
 extern struct fstype *find_fstype_by_name(char *fst);
 
 struct cr_fdset;
-extern int dump_mnt_ns(int pid, int ns_id);
+struct ns_id;
+extern int dump_mnt_ns(struct ns_id *ns);
 extern int prepare_mnt_ns(int pid);
 
 extern int pivot_root(const char *new_root, const char *put_old);
@@ -24,7 +25,6 @@ extern struct ns_desc mnt_ns_desc;
 extern dev_t phys_stat_resolve_dev(dev_t st_dev, const char *path);
 extern bool phys_stat_dev_match(dev_t st_dev, dev_t phys_dev, const char *path);
 
-struct ns_id;
 extern int restore_task_mnt_ns(struct ns_id *nsid, pid_t pid);
 extern int fini_mnt_ns(void);
 

include/namespaces.h

@@ -16,6 +16,11 @@ struct ns_id {
 	struct ns_desc *nd;
 	struct ns_id *next;
 	futex_t created; /* boolean */
+	union {
+		struct {
+			struct mount_info *mntinfo_tree;
+		} mnt;
+	};
 };
 extern struct ns_id *ns_ids;
 

mount.c

@@ -827,10 +827,12 @@ static int dump_one_mountpoint(struct mount_info *pm, int fd)
 	return 0;
 }
 
-int dump_mnt_ns(int ns_pid, int ns_id)
+int dump_mnt_ns(struct ns_id *ns)
 {
 	struct mount_info *pm;
 	int img_fd, ret = -1;
+	int ns_pid = ns->pid;
+	int ns_id = ns->id;
 
 	img_fd = open_image(CR_FD_MNTS, O_DUMP, ns_id);
 	if (img_fd < 0)
@@ -845,7 +847,8 @@ int dump_mnt_ns(int ns_pid, int ns_id)
 		goto err;
 	}
 
-	if (mnt_build_tree(pm) == NULL)
+	ns->mnt.mntinfo_tree = mnt_build_tree(pm);
+	if (ns->mnt.mntinfo_tree == NULL)
 		goto err;
 
 	if (validate_mounts(pm, true))
@@ -859,7 +862,6 @@ int dump_mnt_ns(int ns_pid, int ns_id)
 		if (dump_one_mountpoint(pm, img_fd))
 			goto err;
 
-		xfree(pm);
 		pm = n;
 	} while (pm);
 

namespaces.c

@@ -461,7 +461,7 @@ int dump_mnt_namespaces(void)
 
 		pr_info("Dump MNT namespace (mountpoints) %d via %d\n",
 				ns->id, ns->pid);
-		ret = dump_mnt_ns(ns->pid, ns->id);
+		ret = dump_mnt_ns(ns);
 		if (ret)
 			break;
 	}