Merge tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull notification queue from David Howells:
 "This adds a general notification queue concept and adds an event
  source for keys/keyrings, such as linking and unlinking keys and
  changing their attributes.

  Thanks to Debarshi Ray, we do have a pull request to use this to fix a
  problem with gnome-online-accounts - as mentioned last time:

     https://gitlab.gnome.org/GNOME/gnome-online-accounts/merge_requests/47

  Without this, g-o-a has to constantly poll a keyring-based kerberos
  cache to find out if kinit has changed anything.

  [ There are other notification pending: mount/sb fsinfo notifications
    for libmount that Karel Zak and Ian Kent have been working on, and
    Christian Brauner would like to use them in lxc, but let's see how
    this one works first ]

  LSM hooks are included:

   - A set of hooks are provided that allow an LSM to rule on whether or
     not a watch may be set. Each of these hooks takes a different
     "watched object" parameter, so they're not really shareable. The
     LSM should use current's credentials. [Wanted by SELinux & Smack]

   - A hook is provided to allow an LSM to rule on whether or not a
     particular message may be posted to a particular queue. This is
     given the credentials from the event generator (which may be the
     system) and the watch setter. [Wanted by Smack]

  I've provided SELinux and Smack with implementations of some of these
  hooks.

  WHY
  ===

  Key/keyring notifications are desirable because if you have your
  kerberos tickets in a file/directory, your Gnome desktop will monitor
  that using something like fanotify and tell you if your credentials
  cache changes.

  However, we also have the ability to cache your kerberos tickets in
  the session, user or persistent keyring so that it isn't left around
  on disk across a reboot or logout. Keyrings, however, cannot currently
  be monitored asynchronously, so the desktop has to poll for it - not
  so good on a laptop. This facility will allow the desktop to avoid the
  need to poll.

  DESIGN DECISIONS
  ================

   - The notification queue is built on top of a standard pipe. Messages
     are effectively spliced in. The pipe is opened with a special flag:

        pipe2(fds, O_NOTIFICATION_PIPE);

     The special flag has the same value as O_EXCL (which doesn't seem
     like it will ever be applicable in this context)[?]. It is given up
     front to make it a lot easier to prohibit splice&co from accessing
     the pipe.

     [?] Should this be done some other way?  I'd rather not use up a new
         O_* flag if I can avoid it - should I add a pipe3() system call
         instead?

     The pipe is then configured::

        ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
        ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter);

     Messages are then read out of the pipe using read().

   - It should be possible to allow write() to insert data into the
     notification pipes too, but this is currently disabled as the
     kernel has to be able to insert messages into the pipe *without*
     holding pipe->mutex and the code to make this work needs careful
     auditing.

   - sendfile(), splice() and vmsplice() are disabled on notification
     pipes because of the pipe->mutex issue and also because they
     sometimes want to revert what they just did - but one or more
     notification messages might've been interleaved in the ring.

   - The kernel inserts messages with the wait queue spinlock held. This
     means that pipe_read() and pipe_write() have to take the spinlock
     to update the queue pointers.

   - Records in the buffer are binary, typed and have a length so that
     they can be of varying size.

     This allows multiple heterogeneous sources to share a common
     buffer; there are 16 million types available, of which I've used
     just a few, so there is scope for others to be used. Tags may be
     specified when a watchpoint is created to help distinguish the
     sources.

   - Records are filterable as types have up to 256 subtypes that can be
     individually filtered. Other filtration is also available.

   - Notification pipes don't interfere with each other; each may be
     bound to a different set of watches. Any particular notification
     will be copied to all the queues that are currently watching for it
     - and only those that are watching for it.

   - When recording a notification, the kernel will not sleep, but will
     rather mark a queue as having lost a message if there's
     insufficient space. read() will fabricate a loss notification
     message at an appropriate point later.

   - The notification pipe is created and then watchpoints are attached
     to it, using one of:

        keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
        watch_mount(AT_FDCWD, "/", 0, fd, 0x02);
        watch_sb(AT_FDCWD, "/mnt", 0, fd, 0x03);

     where in both cases, fd indicates the queue and the number after is
     a tag between 0 and 255.

   - Watches are removed if either the notification pipe is destroyed or
     the watched object is destroyed. In the latter case, a message will
     be generated indicating the enforced watch removal.

  Things I want to avoid:

   - Introducing features that make the core VFS dependent on the
     network stack or networking namespaces (ie. usage of netlink).

   - Dumping all this stuff into dmesg and having a daemon that sits
     there parsing the output and distributing it as this then puts the
     responsibility for security into userspace and makes handling
     namespaces tricky. Further, dmesg might not exist or might be
     inaccessible inside a container.

   - Letting users see events they shouldn't be able to see.

  TESTING AND MANPAGES
  ====================

   - The keyutils tree has a pipe-watch branch that has keyctl commands
     for making use of notifications. Proposed manual pages can also be
     found on this branch, though a couple of them really need to go to
     the main manpages repository instead.

     If the kernel supports the watching of keys, then running "make
     test" on that branch will cause the testing infrastructure to spawn
     a monitoring process on the side that monitors a notifications pipe
     for all the key/keyring changes induced by the tests and they'll
     all be checked off to make sure they happened.

        https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/log/?h=pipe-watch

   - A test program is provided (samples/watch_queue/watch_test) that
     can be used to monitor for keyrings, mount and superblock events.
     Information on the notifications is simply logged to stdout"

* tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  smack: Implement the watch_key and post_notification hooks
  selinux: Implement the watch_key security hook
  keys: Make the KEY_NEED_* perms an enum rather than a mask
  pipe: Add notification lossage handling
  pipe: Allow buffers to be marked read-whole-or-error for notifications
  Add sample notification program
  watch_queue: Add a key/keyring notification facility
  security: Add hooks to rule on setting a watch
  pipe: Add general notification queue support
  pipe: Add O_NOTIFICATION_PIPE
  security: Add a hook for the point of notification insertion
  uapi: General notification queue definitions

9 files changed, 331 insertions, 16 deletions

diff --git a/include/linux/key.h b/include/linux/key.h
index 6cf8e71cf8b7..0f2e24f13c2b 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -71,6 +71,23 @@ struct net;
 
 #define KEY_PERM_UNDEF	0xffffffff
 
+/*
+ * The permissions required on a key that we're looking up.
+ */
+enum key_need_perm {
+	KEY_NEED_UNSPECIFIED,	/* Needed permission unspecified */
+	KEY_NEED_VIEW,		/* Require permission to view attributes */
+	KEY_NEED_READ,		/* Require permission to read content */
+	KEY_NEED_WRITE,		/* Require permission to update / modify */
+	KEY_NEED_SEARCH,	/* Require permission to search (keyring) or find (key) */
+	KEY_NEED_LINK,		/* Require permission to link */
+	KEY_NEED_SETATTR,	/* Require permission to change attributes */
+	KEY_NEED_UNLINK,	/* Require permission to unlink key */
+	KEY_SYSADMIN_OVERRIDE,	/* Special: override by CAP_SYS_ADMIN */
+	KEY_AUTHTOKEN_OVERRIDE,	/* Special: override by possession of auth token */
+	KEY_DEFER_PERM_CHECK,	/* Special: permission check is deferred */
+};
+
 struct seq_file;
 struct user_struct;
 struct signal_struct;
@@ -176,6 +193,9 @@ struct key {
 		struct list_head graveyard_link;
 		struct rb_node	serial_node;
 	};
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	struct watch_list	*watchers;	/* Entities watching this key for changes */
+#endif
 	struct rw_semaphore	sem;		/* change vs change sem */
 	struct key_user		*user;		/* owner of this key */
 	void			*security;	/* security data for this key */
@@ -417,20 +437,9 @@ static inline key_serial_t key_serial(const struct key *key)
 extern void key_set_timeout(struct key *, unsigned);
 
 extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
-				 key_perm_t perm);
+				 enum key_need_perm need_perm);
 extern void key_free_user_ns(struct user_namespace *);
 
-/*
- * The permissions required on a key that we're looking up.
- */
-#define	KEY_NEED_VIEW	0x01	/* Require permission to view attributes */
-#define	KEY_NEED_READ	0x02	/* Require permission to read content */
-#define	KEY_NEED_WRITE	0x04	/* Require permission to update / modify */
-#define	KEY_NEED_SEARCH	0x08	/* Require permission to search (keyring) or find (key) */
-#define	KEY_NEED_LINK	0x10	/* Require permission to link */
-#define	KEY_NEED_SETATTR 0x20	/* Require permission to change attributes */
-#define	KEY_NEED_ALL	0x3f	/* All the above permissions */
-
 static inline short key_read_state(const struct key *key)
 {
 	/* Barrier versus mark_key_instantiated(). */
diff --git a/include/linux/lsm_audit.h b/include/linux/lsm_audit.h
index 99d629fd9944..28f23b341c1c 100644
--- a/include/linux/lsm_audit.h
+++ b/include/linux/lsm_audit.h
@@ -75,6 +75,7 @@ struct common_audit_data {
 #define LSM_AUDIT_DATA_IBPKEY	13
 #define LSM_AUDIT_DATA_IBENDPORT 14
 #define LSM_AUDIT_DATA_LOCKDOWN 15
+#define LSM_AUDIT_DATA_NOTIFICATION 16
 	union 	{
 		struct path path;
 		struct dentry *dentry;
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index fb3ce6cec997..4a3d70baa7f1 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -254,6 +254,15 @@ LSM_HOOK(int, 0, inode_setsecctx, struct dentry *dentry, void *ctx, u32 ctxlen)
 LSM_HOOK(int, 0, inode_getsecctx, struct inode *inode, void **ctx,
 	 u32 *ctxlen)
 
+#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
+LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,
+	 const struct cred *cred, struct watch_notification *n)
+#endif /* CONFIG_SECURITY && CONFIG_WATCH_QUEUE */
+
+#if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
+LSM_HOOK(int, 0, watch_key, struct key *key)
+#endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */
+
 #ifdef CONFIG_SECURITY_NETWORK
 LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,
 	 struct sock *newsk)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 3e62dab77699..73d87955e26b 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1445,6 +1445,20 @@
  *	@ctx is a pointer in which to place the allocated security context.
  *	@ctxlen points to the place to put the length of @ctx.
  *
+ * Security hooks for the general notification queue:
+ *
+ * @post_notification:
+ *	Check to see if a watch notification can be posted to a particular
+ *	queue.
+ *	@w_cred: The credentials of the whoever set the watch.
+ *	@cred: The event-triggerer's credentials
+ *	@n: The notification being posted
+ *
+ * @watch_key:
+ *	Check to see if a process is allowed to watch for event notifications
+ *	from a key or keyring.
+ *	@key: The key to watch.
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 0c31b9461262..50afd0d0084c 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -9,6 +9,10 @@
 #define PIPE_BUF_FLAG_GIFT	0x04	/* page is a gift */
 #define PIPE_BUF_FLAG_PACKET	0x08	/* read() as a packet */
 #define PIPE_BUF_FLAG_CAN_MERGE	0x10	/* can merge buffers */
+#define PIPE_BUF_FLAG_WHOLE	0x20	/* read() must return entire buffer or error */
+#ifdef CONFIG_WATCH_QUEUE
+#define PIPE_BUF_FLAG_LOSS	0x40	/* Message loss happened after this buffer */
+#endif
 
 /**
  *	struct pipe_buffer - a linux kernel pipe buffer
@@ -34,8 +38,10 @@ struct pipe_buffer {
  *	@wr_wait: writer wait point in case of full pipe
  *	@head: The point of buffer production
  *	@tail: The point of buffer consumption
+ *	@note_loss: The next read() should insert a data-lost message
  *	@max_usage: The maximum number of slots that may be used in the ring
  *	@ring_size: total number of buffers (should be a power of 2)
+ *	@nr_accounted: The amount this pipe accounts for in user->pipe_bufs
  *	@tmp_page: cached released page
  *	@readers: number of current readers of this pipe
  *	@writers: number of current writers of this pipe
@@ -46,6 +52,7 @@ struct pipe_buffer {
  *	@fasync_writers: writer side fasync
  *	@bufs: the circular array of pipe buffers
  *	@user: the user who created this pipe
+ *	@watch_queue: If this pipe is a watch_queue, this is the stuff for that
  **/
 struct pipe_inode_info {
 	struct mutex mutex;
@@ -54,6 +61,10 @@ struct pipe_inode_info {
 	unsigned int tail;
 	unsigned int max_usage;
 	unsigned int ring_size;
+#ifdef CONFIG_WATCH_QUEUE
+	bool note_loss;
+#endif
+	unsigned int nr_accounted;
 	unsigned int readers;
 	unsigned int writers;
 	unsigned int files;
@@ -64,6 +75,9 @@ struct pipe_inode_info {
 	struct fasync_struct *fasync_writers;
 	struct pipe_buffer *bufs;
 	struct user_struct *user;
+#ifdef CONFIG_WATCH_QUEUE
+	struct watch_queue *watch_queue;
+#endif
 };
 
 /*
@@ -239,9 +253,20 @@ void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
 
 extern const struct pipe_buf_operations nosteal_pipe_buf_ops;
 
+#ifdef CONFIG_WATCH_QUEUE
+unsigned long account_pipe_buffers(struct user_struct *user,
+				   unsigned long old, unsigned long new);
+bool too_many_pipe_buffers_soft(unsigned long user_bufs);
+bool too_many_pipe_buffers_hard(unsigned long user_bufs);
+bool pipe_is_unprivileged_user(void);
+#endif
+
 /* for F_SETPIPE_SZ and F_GETPIPE_SZ */
+#ifdef CONFIG_WATCH_QUEUE
+int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots);
+#endif
 long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
-struct pipe_inode_info *get_pipe_info(struct file *file);
+struct pipe_inode_info *get_pipe_info(struct file *file, bool for_splice);
 
 int create_pipe_files(struct file **, int);
 unsigned int round_pipe_size(unsigned long size);
diff --git a/include/linux/security.h b/include/linux/security.h
index b3f2cb21b4f2..469fa91f8cf8 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -56,6 +56,8 @@ struct mm_struct;
 struct fs_context;
 struct fs_parameter;
 enum fs_value_type;
+struct watch;
+struct watch_notification;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
@@ -1282,6 +1284,28 @@ static inline int security_locked_down(enum lockdown_reason what)
 }
 #endif	/* CONFIG_SECURITY */
 
+#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
+int security_post_notification(const struct cred *w_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n);
+#else
+static inline int security_post_notification(const struct cred *w_cred,
+					     const struct cred *cred,
+					     struct watch_notification *n)
+{
+	return 0;
+}
+#endif
+
+#if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
+int security_watch_key(struct key *key);
+#else
+static inline int security_watch_key(struct key *key)
+{
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk);
@@ -1750,8 +1774,8 @@ static inline int security_path_chroot(const struct path *path)
 
 int security_key_alloc(struct key *key, const struct cred *cred, unsigned long flags);
 void security_key_free(struct key *key);
-int security_key_permission(key_ref_t key_ref,
-			    const struct cred *cred, unsigned perm);
+int security_key_permission(key_ref_t key_ref, const struct cred *cred,
+			    enum key_need_perm need_perm);
 int security_key_getsecurity(struct key *key, char **_buffer);
 
 #else
@@ -1769,7 +1793,7 @@ static inline void security_key_free(struct key *key)
 
 static inline int security_key_permission(key_ref_t key_ref,
 					  const struct cred *cred,
-					  unsigned perm)
+					  enum key_need_perm need_perm)
 {
 	return 0;
 }
diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
new file mode 100644
index 000000000000..5e08db2adc31
--- /dev/null
+++ b/include/linux/watch_queue.h
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ *
+ * See Documentation/watch_queue.rst
+ */
+
+#ifndef _LINUX_WATCH_QUEUE_H
+#define _LINUX_WATCH_QUEUE_H
+
+#include <uapi/linux/watch_queue.h>
+#include <linux/kref.h>
+#include <linux/rcupdate.h>
+
+#ifdef CONFIG_WATCH_QUEUE
+
+struct cred;
+
+struct watch_type_filter {
+	enum watch_notification_type type;
+	__u32		subtype_filter[1];	/* Bitmask of subtypes to filter on */
+	__u32		info_filter;		/* Filter on watch_notification::info */
+	__u32		info_mask;		/* Mask of relevant bits in info_filter */
+};
+
+struct watch_filter {
+	union {
+		struct rcu_head	rcu;
+		unsigned long	type_filter[2];	/* Bitmask of accepted types */
+	};
+	u32			nr_filters;	/* Number of filters */
+	struct watch_type_filter filters[];
+};
+
+struct watch_queue {
+	struct rcu_head		rcu;
+	struct watch_filter __rcu *filter;
+	struct pipe_inode_info	*pipe;		/* The pipe we're using as a buffer */
+	struct hlist_head	watches;	/* Contributory watches */
+	struct page		**notes;	/* Preallocated notifications */
+	unsigned long		*notes_bitmap;	/* Allocation bitmap for notes */
+	struct kref		usage;		/* Object usage count */
+	spinlock_t		lock;
+	unsigned int		nr_notes;	/* Number of notes */
+	unsigned int		nr_pages;	/* Number of pages in notes[] */
+	bool			defunct;	/* T when queues closed */
+};
+
+/*
+ * Representation of a watch on an object.
+ */
+struct watch {
+	union {
+		struct rcu_head	rcu;
+		u32		info_id;	/* ID to be OR'd in to info field */
+	};
+	struct watch_queue __rcu *queue;	/* Queue to post events to */
+	struct hlist_node	queue_node;	/* Link in queue->watches */
+	struct watch_list __rcu	*watch_list;
+	struct hlist_node	list_node;	/* Link in watch_list->watchers */
+	const struct cred	*cred;		/* Creds of the owner of the watch */
+	void			*private;	/* Private data for the watched object */
+	u64			id;		/* Internal identifier */
+	struct kref		usage;		/* Object usage count */
+};
+
+/*
+ * List of watches on an object.
+ */
+struct watch_list {
+	struct rcu_head		rcu;
+	struct hlist_head	watchers;
+	void (*release_watch)(struct watch *);
+	spinlock_t		lock;
+};
+
+extern void __post_watch_notification(struct watch_list *,
+				      struct watch_notification *,
+				      const struct cred *,
+				      u64);
+extern struct watch_queue *get_watch_queue(int);
+extern void put_watch_queue(struct watch_queue *);
+extern void init_watch(struct watch *, struct watch_queue *);
+extern int add_watch_to_object(struct watch *, struct watch_list *);
+extern int remove_watch_from_object(struct watch_list *, struct watch_queue *, u64, bool);
+extern long watch_queue_set_size(struct pipe_inode_info *, unsigned int);
+extern long watch_queue_set_filter(struct pipe_inode_info *,
+				   struct watch_notification_filter __user *);
+extern int watch_queue_init(struct pipe_inode_info *);
+extern void watch_queue_clear(struct watch_queue *);
+
+static inline void init_watch_list(struct watch_list *wlist,
+				   void (*release_watch)(struct watch *))
+{
+	INIT_HLIST_HEAD(&wlist->watchers);
+	spin_lock_init(&wlist->lock);
+	wlist->release_watch = release_watch;
+}
+
+static inline void post_watch_notification(struct watch_list *wlist,
+					   struct watch_notification *n,
+					   const struct cred *cred,
+					   u64 id)
+{
+	if (unlikely(wlist))
+		__post_watch_notification(wlist, n, cred, id);
+}
+
+static inline void remove_watch_list(struct watch_list *wlist, u64 id)
+{
+	if (wlist) {
+		remove_watch_from_object(wlist, NULL, id, true);
+		kfree_rcu(wlist, rcu);
+	}
+}
+
+/**
+ * watch_sizeof - Calculate the information part of the size of a watch record,
+ * given the structure size.
+ */
+#define watch_sizeof(STRUCT) (sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT)
+
+#endif
+
+#endif /* _LINUX_WATCH_QUEUE_H */
diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h
index ed3d5893830d..4c8884eea808 100644
--- a/include/uapi/linux/keyctl.h
+++ b/include/uapi/linux/keyctl.h
@@ -69,6 +69,7 @@
 #define KEYCTL_RESTRICT_KEYRING		29	/* Restrict keys allowed to link to a keyring */
 #define KEYCTL_MOVE			30	/* Move keys between keyrings */
 #define KEYCTL_CAPABILITIES		31	/* Find capabilities of keyrings subsystem */
+#define KEYCTL_WATCH_KEY		32	/* Watch a key or ring of keys for changes */
 
 /* keyctl structures */
 struct keyctl_dh_params {
@@ -130,5 +131,6 @@ struct keyctl_pkey_params {
 #define KEYCTL_CAPS0_MOVE		0x80 /* KEYCTL_MOVE supported */
 #define KEYCTL_CAPS1_NS_KEYRING_NAME	0x01 /* Keyring names are per-user_namespace */
 #define KEYCTL_CAPS1_NS_KEY_TAG		0x02 /* Key indexing can include a namespace tag */
+#define KEYCTL_CAPS1_NOTIFICATIONS	0x04 /* Keys generate watchable notifications */
 
 #endif /*  _LINUX_KEYCTL_H */
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
new file mode 100644
index 000000000000..c3d8320b5d3a
--- /dev/null
+++ b/include/uapi/linux/watch_queue.h
@@ -0,0 +1,104 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_WATCH_QUEUE_H
+#define _UAPI_LINUX_WATCH_QUEUE_H
+
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/ioctl.h>
+
+#define O_NOTIFICATION_PIPE	O_EXCL	/* Parameter to pipe2() selecting notification pipe */
+
+#define IOC_WATCH_QUEUE_SET_SIZE	_IO('W', 0x60)	/* Set the size in pages */
+#define IOC_WATCH_QUEUE_SET_FILTER	_IO('W', 0x61)	/* Set the filter */
+
+enum watch_notification_type {
+	WATCH_TYPE_META		= 0,	/* Special record */
+	WATCH_TYPE_KEY_NOTIFY	= 1,	/* Key change event notification */
+	WATCH_TYPE__NR		= 2
+};
+
+enum watch_meta_notification_subtype {
+	WATCH_META_REMOVAL_NOTIFICATION	= 0,	/* Watched object was removed */
+	WATCH_META_LOSS_NOTIFICATION	= 1,	/* Data loss occurred */
+};
+
+/*
+ * Notification record header.  This is aligned to 64-bits so that subclasses
+ * can contain __u64 fields.
+ */
+struct watch_notification {
+	__u32			type:24;	/* enum watch_notification_type */
+	__u32			subtype:8;	/* Type-specific subtype (filterable) */
+	__u32			info;
+#define WATCH_INFO_LENGTH	0x0000007f	/* Length of record */
+#define WATCH_INFO_LENGTH__SHIFT 0
+#define WATCH_INFO_ID		0x0000ff00	/* ID of watchpoint */
+#define WATCH_INFO_ID__SHIFT	8
+#define WATCH_INFO_TYPE_INFO	0xffff0000	/* Type-specific info */
+#define WATCH_INFO_TYPE_INFO__SHIFT 16
+#define WATCH_INFO_FLAG_0	0x00010000	/* Type-specific info, flag bit 0 */
+#define WATCH_INFO_FLAG_1	0x00020000	/* ... */
+#define WATCH_INFO_FLAG_2	0x00040000
+#define WATCH_INFO_FLAG_3	0x00080000
+#define WATCH_INFO_FLAG_4	0x00100000
+#define WATCH_INFO_FLAG_5	0x00200000
+#define WATCH_INFO_FLAG_6	0x00400000
+#define WATCH_INFO_FLAG_7	0x00800000
+};
+
+/*
+ * Notification filtering rules (IOC_WATCH_QUEUE_SET_FILTER).
+ */
+struct watch_notification_type_filter {
+	__u32	type;			/* Type to apply filter to */
+	__u32	info_filter;		/* Filter on watch_notification::info */
+	__u32	info_mask;		/* Mask of relevant bits in info_filter */
+	__u32	subtype_filter[8];	/* Bitmask of subtypes to filter on */
+};
+
+struct watch_notification_filter {
+	__u32	nr_filters;		/* Number of filters */
+	__u32	__reserved;		/* Must be 0 */
+	struct watch_notification_type_filter filters[];
+};
+
+
+/*
+ * Extended watch removal notification.  This is used optionally if the type
+ * wants to indicate an identifier for the object being watched, if there is
+ * such.  This can be distinguished by the length.
+ *
+ * type -> WATCH_TYPE_META
+ * subtype -> WATCH_META_REMOVAL_NOTIFICATION
+ */
+struct watch_notification_removal {
+	struct watch_notification watch;
+	__u64	id;		/* Type-dependent identifier */
+};
+
+/*
+ * Type of key/keyring change notification.
+ */
+enum key_notification_subtype {
+	NOTIFY_KEY_INSTANTIATED	= 0, /* Key was instantiated (aux is error code) */
+	NOTIFY_KEY_UPDATED	= 1, /* Key was updated */
+	NOTIFY_KEY_LINKED	= 2, /* Key (aux) was added to watched keyring */
+	NOTIFY_KEY_UNLINKED	= 3, /* Key (aux) was removed from watched keyring */
+	NOTIFY_KEY_CLEARED	= 4, /* Keyring was cleared */
+	NOTIFY_KEY_REVOKED	= 5, /* Key was revoked */
+	NOTIFY_KEY_INVALIDATED	= 6, /* Key was invalidated */
+	NOTIFY_KEY_SETATTR	= 7, /* Key's attributes got changed */
+};
+
+/*
+ * Key/keyring notification record.
+ * - watch.type = WATCH_TYPE_KEY_NOTIFY
+ * - watch.subtype = enum key_notification_type
+ */
+struct key_notification {
+	struct watch_notification watch;
+	__u32	key_id;		/* The key/keyring affected */
+	__u32	aux;		/* Per-type auxiliary data */
+};
+
+#endif /* _UAPI_LINUX_WATCH_QUEUE_H */