4 files changed, 52 insertions, 2 deletions
diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
index 3f05dd7d40c7..bd4492ef6ffc 100644
--- a/include/linux/ns_common.h
+++ b/include/linux/ns_common.h
@@ -129,8 +129,10 @@ struct ns_common {
 	};
 };
 
+bool is_current_namespace(struct ns_common *ns);
 int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_operations *ops, int inum);
 void __ns_common_free(struct ns_common *ns);
+struct ns_common *__must_check ns_owner(struct ns_common *ns);
 
 static __always_inline bool is_initial_namespace(struct ns_common *ns)
 {
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 66c06fcdfe19..cf84d98964b2 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -77,6 +77,7 @@ struct cachestat_range;
 struct cachestat;
 struct statmount;
 struct mnt_id_req;
+struct ns_id_req;
 struct xattr_args;
 struct file_attr;
 
@@ -437,6 +438,9 @@ asmlinkage long sys_statmount(const struct mnt_id_req __user *req,
 asmlinkage long sys_listmount(const struct mnt_id_req __user *req,
 			      u64 __user *mnt_ids, size_t nr_mnt_ids,
 			      unsigned int flags);
+asmlinkage long sys_listns(const struct ns_id_req __user *req,
+			   u64 __user *ns_ids, size_t nr_ns_ids,
+			   unsigned int flags);
 asmlinkage long sys_truncate(const char __user *path, long length);
 asmlinkage long sys_ftruncate(unsigned int fd, off_t length);
 #if BITS_PER_LONG == 32
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 9a9aebbf96b9..9c3be157397e 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -166,13 +166,13 @@ static inline void set_userns_rlimit_max(struct user_namespace *ns,
 	ns->rlimit_max[type] = max <= LONG_MAX ? max : LONG_MAX;
 }
 
-#ifdef CONFIG_USER_NS
-
 static inline struct user_namespace *to_user_ns(struct ns_common *ns)
 {
 	return container_of(ns, struct user_namespace, ns);
 }
 
+#ifdef CONFIG_USER_NS
+
 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
 {
 	if (ns)
diff --git a/include/uapi/linux/nsfs.h b/include/uapi/linux/nsfs.h
index f8bc2aad74d6..a25e38d1c874 100644
--- a/include/uapi/linux/nsfs.h
+++ b/include/uapi/linux/nsfs.h
@@ -81,4 +81,48 @@ enum init_ns_id {
 #endif
 };
 
+enum ns_type {
+	TIME_NS    = (1ULL << 7),  /* CLONE_NEWTIME */
+	MNT_NS     = (1ULL << 17), /* CLONE_NEWNS */
+	CGROUP_NS  = (1ULL << 25), /* CLONE_NEWCGROUP */
+	UTS_NS     = (1ULL << 26), /* CLONE_NEWUTS */
+	IPC_NS     = (1ULL << 27), /* CLONE_NEWIPC */
+	USER_NS    = (1ULL << 28), /* CLONE_NEWUSER */
+	PID_NS     = (1ULL << 29), /* CLONE_NEWPID */
+	NET_NS     = (1ULL << 30), /* CLONE_NEWNET */
+};
+
+/**
+ * struct ns_id_req - namespace ID request structure
+ * @size: size of this structure
+ * @spare: reserved for future use
+ * @filter: filter mask
+ * @ns_id: last namespace id
+ * @user_ns_id: owning user namespace ID
+ *
+ * Structure for passing namespace ID and miscellaneous parameters to
+ * statns(2) and listns(2).
+ *
+ * For statns(2) @param represents the request mask.
+ * For listns(2) @param represents the last listed mount id (or zero).
+ */
+struct ns_id_req {
+	__u32 size;
+	__u32 spare;
+	__u64 ns_id;
+	struct /* listns */ {
+		__u32 ns_type;
+		__u32 spare2;
+		__u64 user_ns_id;
+	};
+};
+
+/*
+ * Special @user_ns_id value that can be passed to listns()
+ */
+#define LISTNS_CURRENT_USER 0xffffffffffffffff /* Caller's userns */
+
+/* List of all ns_id_req versions. */
+#define NS_ID_REQ_SIZE_VER0 32 /* sizeof first published struct */
+
 #endif /* __LINUX_NSFS_H */