ns: move namespace types into separate header

Add a dedicated header for namespace types.

Link: https://patch.msgid.link/20251110-work-namespace-nstree-fixes-v1-1-e8a9264e0fb9@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 205 insertions, 0 deletions

diff --git a/include/linux/ns/ns_common_types.h b/include/linux/ns/ns_common_types.h
new file mode 100644
index 000000000000..ccd1d1e116f6
--- /dev/null
+++ b/include/linux/ns/ns_common_types.h
@@ -0,0 +1,205 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_NS_COMMON_TYPES_H
+#define _LINUX_NS_COMMON_TYPES_H
+
+#include <linux/atomic.h>
+#include <linux/rbtree.h>
+#include <linux/refcount.h>
+#include <linux/types.h>
+
+struct cgroup_namespace;
+struct dentry;
+struct ipc_namespace;
+struct mnt_namespace;
+struct net;
+struct pid_namespace;
+struct proc_ns_operations;
+struct time_namespace;
+struct user_namespace;
+struct uts_namespace;
+
+extern struct cgroup_namespace init_cgroup_ns;
+extern struct ipc_namespace init_ipc_ns;
+extern struct mnt_namespace init_mnt_ns;
+extern struct net init_net;
+extern struct pid_namespace init_pid_ns;
+extern struct time_namespace init_time_ns;
+extern struct user_namespace init_user_ns;
+extern struct uts_namespace init_uts_ns;
+
+extern const struct proc_ns_operations cgroupns_operations;
+extern const struct proc_ns_operations ipcns_operations;
+extern const struct proc_ns_operations mntns_operations;
+extern const struct proc_ns_operations netns_operations;
+extern const struct proc_ns_operations pidns_operations;
+extern const struct proc_ns_operations pidns_for_children_operations;
+extern const struct proc_ns_operations timens_operations;
+extern const struct proc_ns_operations timens_for_children_operations;
+extern const struct proc_ns_operations userns_operations;
+extern const struct proc_ns_operations utsns_operations;
+
+/*
+ * Namespace lifetimes are managed via a two-tier reference counting model:
+ *
+ * (1) __ns_ref (refcount_t): Main reference count tracking memory
+ *     lifetime. Controls when the namespace structure itself is freed.
+ *     It also pins the namespace on the namespace trees whereas (2)
+ *     only regulates their visibility to userspace.
+ *
+ * (2) __ns_ref_active (atomic_t): Reference count tracking active users.
+ *     Controls visibility of the namespace in the namespace trees.
+ *     Any live task that uses the namespace (via nsproxy or cred) holds
+ *     an active reference. Any open file descriptor or bind-mount of
+ *     the namespace holds an active reference. Once all tasks have
+ *     called exited their namespaces and all file descriptors and
+ *     bind-mounts have been released the active reference count drops
+ *     to zero and the namespace becomes inactive. IOW, the namespace
+ *     cannot be listed or opened via file handles anymore.
+ *
+ *     Note that it is valid to transition from active to inactive and
+ *     back from inactive to active e.g., when resurrecting an inactive
+ *     namespace tree via the SIOCGSKNS ioctl().
+ *
+ * Relationship and lifecycle states:
+ *
+ * - Active (__ns_ref_active > 0):
+ *   Namespace is actively used and visible to userspace. The namespace
+ *   can be reopened via /proc/<pid>/ns/<ns_type>, via namespace file
+ *   handles, or discovered via listns().
+ *
+ * - Inactive (__ns_ref_active == 0, __ns_ref > 0):
+ *   No tasks are actively using the namespace and it isn't pinned by
+ *   any bind-mounts or open file descriptors anymore. But the namespace
+ *   is still kept alive by internal references. For example, the user
+ *   namespace could be pinned by an open file through file->f_cred
+ *   references when one of the now defunct tasks had opened a file and
+ *   handed the file descriptor off to another process via a UNIX
+ *   sockets. Such references keep the namespace structure alive through
+ *   __ns_ref but will not hold an active reference.
+ *
+ * - Destroyed (__ns_ref == 0):
+ *   No references remain. The namespace is removed from the tree and freed.
+ *
+ * State transitions:
+ *
+ * Active -> Inactive:
+ *   When the last task using the namespace exits it drops its active
+ *   references to all namespaces. However, user and pid namespaces
+ *   remain accessible until the task has been reaped.
+ *
+ * Inactive -> Active:
+ *   An inactive namespace tree might be resurrected due to e.g., the
+ *   SIOCGSKNS ioctl() on a socket.
+ *
+ * Inactive -> Destroyed:
+ *   When __ns_ref drops to zero the namespace is removed from the
+ *   namespaces trees and the memory is freed (after RCU grace period).
+ *
+ * Initial namespaces:
+ *   Boot-time namespaces (init_net, init_pid_ns, etc.) start with
+ *   __ns_ref_active = 1 and remain active forever.
+ */
+struct ns_common {
+	u32 ns_type;
+	struct dentry *stashed;
+	const struct proc_ns_operations *ops;
+	unsigned int inum;
+	refcount_t __ns_ref; /* do not use directly */
+	union {
+		struct {
+			u64 ns_id;
+			struct /* global namespace rbtree and list */ {
+				struct rb_node ns_unified_tree_node;
+				struct list_head ns_unified_list_node;
+			};
+			struct /* per type rbtree and list */ {
+				struct rb_node ns_tree_node;
+				struct list_head ns_list_node;
+			};
+			struct /* namespace ownership rbtree and list */ {
+				struct rb_root ns_owner_tree; /* rbtree of namespaces owned by this namespace */
+				struct list_head ns_owner; /* list of namespaces owned by this namespace */
+				struct rb_node ns_owner_tree_node; /* node in the owner namespace's rbtree */
+				struct list_head ns_owner_entry; /* node in the owner namespace's ns_owned list */
+			};
+			atomic_t __ns_ref_active; /* do not use directly */
+		};
+		struct rcu_head ns_rcu;
+	};
+};
+
+#define to_ns_common(__ns)                                    \
+	_Generic((__ns),                                      \
+		struct cgroup_namespace *:       &(__ns)->ns, \
+		const struct cgroup_namespace *: &(__ns)->ns, \
+		struct ipc_namespace *:          &(__ns)->ns, \
+		const struct ipc_namespace *:    &(__ns)->ns, \
+		struct mnt_namespace *:          &(__ns)->ns, \
+		const struct mnt_namespace *:    &(__ns)->ns, \
+		struct net *:                    &(__ns)->ns, \
+		const struct net *:              &(__ns)->ns, \
+		struct pid_namespace *:          &(__ns)->ns, \
+		const struct pid_namespace *:    &(__ns)->ns, \
+		struct time_namespace *:         &(__ns)->ns, \
+		const struct time_namespace *:   &(__ns)->ns, \
+		struct user_namespace *:         &(__ns)->ns, \
+		const struct user_namespace *:   &(__ns)->ns, \
+		struct uts_namespace *:          &(__ns)->ns, \
+		const struct uts_namespace *:    &(__ns)->ns)
+
+#define ns_init_inum(__ns)                                     \
+	_Generic((__ns),                                       \
+		struct cgroup_namespace *: CGROUP_NS_INIT_INO, \
+		struct ipc_namespace *:    IPC_NS_INIT_INO,    \
+		struct mnt_namespace *:    MNT_NS_INIT_INO,    \
+		struct net *:              NET_NS_INIT_INO,    \
+		struct pid_namespace *:    PID_NS_INIT_INO,    \
+		struct time_namespace *:   TIME_NS_INIT_INO,   \
+		struct user_namespace *:   USER_NS_INIT_INO,   \
+		struct uts_namespace *:    UTS_NS_INIT_INO)
+
+#define ns_init_ns(__ns)                                    \
+	_Generic((__ns),                                    \
+		struct cgroup_namespace *: &init_cgroup_ns, \
+		struct ipc_namespace *:    &init_ipc_ns,    \
+		struct mnt_namespace *:    &init_mnt_ns,     \
+		struct net *:              &init_net,       \
+		struct pid_namespace *:    &init_pid_ns,    \
+		struct time_namespace *:   &init_time_ns,   \
+		struct user_namespace *:   &init_user_ns,   \
+		struct uts_namespace *:    &init_uts_ns)
+
+#define ns_init_id(__ns)						\
+	_Generic((__ns),						\
+		struct cgroup_namespace *:	CGROUP_NS_INIT_ID,	\
+		struct ipc_namespace *:		IPC_NS_INIT_ID,		\
+		struct mnt_namespace *:		MNT_NS_INIT_ID,		\
+		struct net *:			NET_NS_INIT_ID,		\
+		struct pid_namespace *:		PID_NS_INIT_ID,		\
+		struct time_namespace *:	TIME_NS_INIT_ID,	\
+		struct user_namespace *:	USER_NS_INIT_ID,	\
+		struct uts_namespace *:		UTS_NS_INIT_ID)
+
+#define to_ns_operations(__ns)                                                                         \
+	_Generic((__ns),                                                                               \
+		struct cgroup_namespace *: (IS_ENABLED(CONFIG_CGROUPS) ? &cgroupns_operations : NULL), \
+		struct ipc_namespace *:    (IS_ENABLED(CONFIG_IPC_NS)  ? &ipcns_operations    : NULL), \
+		struct mnt_namespace *:    &mntns_operations,                                          \
+		struct net *:              (IS_ENABLED(CONFIG_NET_NS)  ? &netns_operations    : NULL), \
+		struct pid_namespace *:    (IS_ENABLED(CONFIG_PID_NS)  ? &pidns_operations    : NULL), \
+		struct time_namespace *:   (IS_ENABLED(CONFIG_TIME_NS) ? &timens_operations   : NULL), \
+		struct user_namespace *:   (IS_ENABLED(CONFIG_USER_NS) ? &userns_operations   : NULL), \
+		struct uts_namespace *:    (IS_ENABLED(CONFIG_UTS_NS)  ? &utsns_operations    : NULL))
+
+#define ns_common_type(__ns)                                \
+	_Generic((__ns),                                    \
+		struct cgroup_namespace *: CLONE_NEWCGROUP, \
+		struct ipc_namespace *:    CLONE_NEWIPC,    \
+		struct mnt_namespace *:    CLONE_NEWNS,     \
+		struct net *:              CLONE_NEWNET,    \
+		struct pid_namespace *:    CLONE_NEWPID,    \
+		struct time_namespace *:   CLONE_NEWTIME,   \
+		struct user_namespace *:   CLONE_NEWUSER,   \
+		struct uts_namespace *:    CLONE_NEWUTS)
+
+#endif /* _LINUX_NS_COMMON_TYPES_H */