From f5461124d59bfb62bd9e231ee64cbaf757343ad5 Mon Sep 17 00:00:00 2001
From: Randy Dunlap <rdunlap@infradead.org>
Date: Mon, 18 Apr 2022 19:54:16 -0700
Subject: [PATCH] Documentation: move watch_queue to core-api
Git-commit: f5461124d59bfb62bd9e231ee64cbaf757343ad5
Patch-mainline: v5.19-rc1
References: git-fixes
Move watch_queue documentation to the core-api index and
subdirectory.
Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
Documentation/core-api/index.rst | 1
Documentation/core-api/watch_queue.rst | 343 +++++++++++++++++++++++++++++++++
Documentation/index.rst | 1
Documentation/watch_queue.rst | 343 ---------------------------------
4 files changed, 344 insertions(+), 344 deletions(-)
create mode 100644 Documentation/core-api/watch_queue.rst
delete mode 100644 Documentation/watch_queue.rst
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -18,6 +18,7 @@ it.
kernel-api
workqueue
+ watch_queue
printk-basics
printk-formats
symbol-namespaces
--- /dev/null
+++ b/Documentation/core-api/watch_queue.rst
@@ -0,0 +1,343 @@
+==============================
+General notification mechanism
+==============================
+
+The general notification mechanism is built on top of the standard pipe driver
+whereby it effectively splices notification messages from the kernel into pipes
+opened by userspace. This can be used in conjunction with::
+
+ * Key/keyring notifications
+
+
+The notifications buffers can be enabled by:
+
+ "General setup"/"General notification queue"
+ (CONFIG_WATCH_QUEUE)
+
+This document has the following sections:
+
+.. contents:: :local:
+
+
+Overview
+========
+
+This facility appears as a pipe that is opened in a special mode. The pipe's
+internal ring buffer is used to hold messages that are generated by the kernel.
+These messages are then read out by read(). Splice and similar are disabled on
+such pipes due to them wanting to, under some circumstances, revert their
+additions to the ring - which might end up interleaved with notification
+messages.
+
+The owner of the pipe has to tell the kernel which sources it would like to
+watch through that pipe. Only sources that have been connected to a pipe will
+insert messages into it. Note that a source may be bound to multiple pipes and
+insert messages into all of them simultaneously.
+
+Filters may also be emplaced on a pipe so that certain source types and
+subevents can be ignored if they're not of interest.
+
+A message will be discarded if there isn't a slot available in the ring or if
+no preallocated message buffer is available. In both of these cases, read()
+will insert a WATCH_META_LOSS_NOTIFICATION message into the output buffer after
+the last message currently in the buffer has been read.
+
+Note that when producing a notification, the kernel does not wait for the
+consumers to collect it, but rather just continues on. This means that
+notifications can be generated whilst spinlocks are held and also protects the
+kernel from being held up indefinitely by a userspace malfunction.
+
+
+Message Structure
+=================
+
+Notification messages begin with a short header::
+
+ struct watch_notification {
+ __u32 type:24;
+ __u32 subtype:8;
+ __u32 info;
+ };
+
+"type" indicates the source of the notification record and "subtype" indicates
+the type of record from that source (see the Watch Sources section below). The
+type may also be "WATCH_TYPE_META". This is a special record type generated
+internally by the watch queue itself. There are two subtypes:
+
+ * WATCH_META_REMOVAL_NOTIFICATION
+ * WATCH_META_LOSS_NOTIFICATION
+
+The first indicates that an object on which a watch was installed was removed
+or destroyed and the second indicates that some messages have been lost.
+
+"info" indicates a bunch of things, including:
+
+ * The length of the message in bytes, including the header (mask with
+ WATCH_INFO_LENGTH and shift by WATCH_INFO_LENGTH__SHIFT). This indicates
+ the size of the record, which may be between 8 and 127 bytes.
+
+ * The watch ID (mask with WATCH_INFO_ID and shift by WATCH_INFO_ID__SHIFT).
+ This indicates that caller's ID of the watch, which may be between 0
+ and 255. Multiple watches may share a queue, and this provides a means to
+ distinguish them.
+
+ * A type-specific field (WATCH_INFO_TYPE_INFO). This is set by the
+ notification producer to indicate some meaning specific to the type and
+ subtype.
+
+Everything in info apart from the length can be used for filtering.
+
+The header can be followed by supplementary information. The format of this is
+at the discretion is defined by the type and subtype.
+
+
+Watch List (Notification Source) API
+====================================
+
+A "watch list" is a list of watchers that are subscribed to a source of
+notifications. A list may be attached to an object (say a key or a superblock)
+or may be global (say for device events). From a userspace perspective, a
+non-global watch list is typically referred to by reference to the object it
+belongs to (such as using KEYCTL_NOTIFY and giving it a key serial number to
+watch that specific key).
+
+To manage a watch list, the following functions are provided:
+
+ * ::
+
+ void init_watch_list(struct watch_list *wlist,
+ void (*release_watch)(struct watch *wlist));
+
+ Initialise a watch list. If ``release_watch`` is not NULL, then this
+ indicates a function that should be called when the watch_list object is
+ destroyed to discard any references the watch list holds on the watched
+ object.
+
+ * ``void remove_watch_list(struct watch_list *wlist);``
+
+ This removes all of the watches subscribed to a watch_list and frees them
+ and then destroys the watch_list object itself.
+
+
+Watch Queue (Notification Output) API
+=====================================
+
+A "watch queue" is the buffer allocated by an application that notification
+records will be written into. The workings of this are hidden entirely inside
+of the pipe device driver, but it is necessary to gain a reference to it to set
+a watch. These can be managed with:
+
+ * ``struct watch_queue *get_watch_queue(int fd);``
+
+ Since watch queues are indicated to the kernel by the fd of the pipe that
+ implements the buffer, userspace must hand that fd through a system call.
+ This can be used to look up an opaque pointer to the watch queue from the
+ system call.
+
+ * ``void put_watch_queue(struct watch_queue *wqueue);``
+
+ This discards the reference obtained from ``get_watch_queue()``.
+
+
+Watch Subscription API
+======================
+
+A "watch" is a subscription on a watch list, indicating the watch queue, and
+thus the buffer, into which notification records should be written. The watch
+queue object may also carry filtering rules for that object, as set by
+userspace. Some parts of the watch struct can be set by the driver::
+
+ struct watch {
+ union {
+ u32 info_id; /* ID to be OR'd in to info field */
+ ...
+ };
+ void *private; /* Private data for the watched object */
+ u64 id; /* Internal identifier */
+ ...
+ };
+
+The ``info_id`` value should be an 8-bit number obtained from userspace and
+shifted by WATCH_INFO_ID__SHIFT. This is OR'd into the WATCH_INFO_ID field of
+struct watch_notification::info when and if the notification is written into
+the associated watch queue buffer.
+
+The ``private`` field is the driver's data associated with the watch_list and
+is cleaned up by the ``watch_list::release_watch()`` method.
+
+The ``id`` field is the source's ID. Notifications that are posted with a
+different ID are ignored.
+
+The following functions are provided to manage watches:
+
+ * ``void init_watch(struct watch *watch, struct watch_queue *wqueue);``
+
+ Initialise a watch object, setting its pointer to the watch queue, using
+ appropriate barriering to avoid lockdep complaints.
+
+ * ``int add_watch_to_object(struct watch *watch, struct watch_list *wlist);``
+
+ Subscribe a watch to a watch list (notification source). The
+ driver-settable fields in the watch struct must have been set before this
+ is called.
+
+ * ::
+
+ int remove_watch_from_object(struct watch_list *wlist,
+ struct watch_queue *wqueue,
+ u64 id, false);
+
+ Remove a watch from a watch list, where the watch must match the specified
+ watch queue (``wqueue``) and object identifier (``id``). A notification
+ (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue to
+ indicate that the watch got removed.
+
+ * ``int remove_watch_from_object(struct watch_list *wlist, NULL, 0, true);``
+
+ Remove all the watches from a watch list. It is expected that this will be
+ called preparatory to destruction and that the watch list will be
+ inaccessible to new watches by this point. A notification
+ (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue of each
+ subscribed watch to indicate that the watch got removed.
+
+
+Notification Posting API
+========================
+
+To post a notification to watch list so that the subscribed watches can see it,
+the following function should be used::
+
+ void post_watch_notification(struct watch_list *wlist,
+ struct watch_notification *n,
+ const struct cred *cred,
+ u64 id);
+
+The notification should be preformatted and a pointer to the header (``n``)
+should be passed in. The notification may be larger than this and the size in
+units of buffer slots is noted in ``n->info & WATCH_INFO_LENGTH``.
+
+The ``cred`` struct indicates the credentials of the source (subject) and is
+passed to the LSMs, such as SELinux, to allow or suppress the recording of the
+note in each individual queue according to the credentials of that queue
+(object).
+
+The ``id`` is the ID of the source object (such as the serial number on a key).
+Only watches that have the same ID set in them will see this notification.
+
+
+Watch Sources
+=============
+
+Any particular buffer can be fed from multiple sources. Sources include:
+
+ * WATCH_TYPE_KEY_NOTIFY
+
+ Notifications of this type indicate changes to keys and keyrings, including
+ the changes of keyring contents or the attributes of keys.
+
+ See Documentation/security/keys/core.rst for more information.
+
+
+Event Filtering
+===============
+
+Once a watch queue has been created, a set of filters can be applied to limit
+the events that are received using::
+
+ struct watch_notification_filter filter = {
+ ...
+ };
+ ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter)
+
+The filter description is a variable of type::
+
+ struct watch_notification_filter {
+ __u32 nr_filters;
+ __u32 __reserved;
+ struct watch_notification_type_filter filters[];
+ };
+
+Where "nr_filters" is the number of filters in filters[] and "__reserved"
+should be 0. The "filters" array has elements of the following type::
+
+ struct watch_notification_type_filter {
+ __u32 type;
+ __u32 info_filter;
+ __u32 info_mask;
+ __u32 subtype_filter[8];
+ };
+
+Where:
+
+ * ``type`` is the event type to filter for and should be something like
+ "WATCH_TYPE_KEY_NOTIFY"
+
+ * ``info_filter`` and ``info_mask`` act as a filter on the info field of the
+ notification record. The notification is only written into the buffer if::
+
+ (watch.info & info_mask) == info_filter
+
+ This could be used, for example, to ignore events that are not exactly on
+ the watched point in a mount tree.
+
+ * ``subtype_filter`` is a bitmask indicating the subtypes that are of
+ interest. Bit 0 of subtype_filter[0] corresponds to subtype 0, bit 1 to
+ subtype 1, and so on.
+
+If the argument to the ioctl() is NULL, then the filters will be removed and
+all events from the watched sources will come through.
+
+
+Userspace Code Example
+======================
+
+A buffer is created with something like the following::
+
+ pipe2(fds, O_TMPFILE);
+ ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256);
+
+It can then be set to receive keyring change notifications::
+
+ keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
+
+The notifications can then be consumed by something like the following::
+
+ static void consumer(int rfd, struct watch_queue_buffer *buf)
+ {
+ unsigned char buffer[128];
+ ssize_t buf_len;
+
+ while (buf_len = read(rfd, buffer, sizeof(buffer)),
+ buf_len > 0
+ ) {
+ void *p = buffer;
+ void *end = buffer + buf_len;
+ while (p < end) {
+ union {
+ struct watch_notification n;
+ unsigned char buf1[128];
+ } n;
+ size_t largest, len;
+
+ largest = end - p;
+ if (largest > 128)
+ largest = 128;
+ memcpy(&n, p, largest);
+
+ len = (n->info & WATCH_INFO_LENGTH) >>
+ WATCH_INFO_LENGTH__SHIFT;
+ if (len == 0 || len > largest)
+ return;
+
+ switch (n.n.type) {
+ case WATCH_TYPE_META:
+ got_meta(&n.n);
+ case WATCH_TYPE_KEY_NOTIFY:
+ saw_key_change(&n.n);
+ break;
+ }
+
+ p += len;
+ }
+ }
+ }
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -166,7 +166,6 @@ to ReStructured Text format, or are simp
:maxdepth: 2
staging/index
- watch_queue
Translations
--- a/Documentation/watch_queue.rst
+++ /dev/null
@@ -1,343 +0,0 @@
-==============================
-General notification mechanism
-==============================
-
-The general notification mechanism is built on top of the standard pipe driver
-whereby it effectively splices notification messages from the kernel into pipes
-opened by userspace. This can be used in conjunction with::
-
- * Key/keyring notifications
-
-
-The notifications buffers can be enabled by:
-
- "General setup"/"General notification queue"
- (CONFIG_WATCH_QUEUE)
-
-This document has the following sections:
-
-.. contents:: :local:
-
-
-Overview
-========
-
-This facility appears as a pipe that is opened in a special mode. The pipe's
-internal ring buffer is used to hold messages that are generated by the kernel.
-These messages are then read out by read(). Splice and similar are disabled on
-such pipes due to them wanting to, under some circumstances, revert their
-additions to the ring - which might end up interleaved with notification
-messages.
-
-The owner of the pipe has to tell the kernel which sources it would like to
-watch through that pipe. Only sources that have been connected to a pipe will
-insert messages into it. Note that a source may be bound to multiple pipes and
-insert messages into all of them simultaneously.
-
-Filters may also be emplaced on a pipe so that certain source types and
-subevents can be ignored if they're not of interest.
-
-A message will be discarded if there isn't a slot available in the ring or if
-no preallocated message buffer is available. In both of these cases, read()
-will insert a WATCH_META_LOSS_NOTIFICATION message into the output buffer after
-the last message currently in the buffer has been read.
-
-Note that when producing a notification, the kernel does not wait for the
-consumers to collect it, but rather just continues on. This means that
-notifications can be generated whilst spinlocks are held and also protects the
-kernel from being held up indefinitely by a userspace malfunction.
-
-
-Message Structure
-=================
-
-Notification messages begin with a short header::
-
- struct watch_notification {
- __u32 type:24;
- __u32 subtype:8;
- __u32 info;
- };
-
-"type" indicates the source of the notification record and "subtype" indicates
-the type of record from that source (see the Watch Sources section below). The
-type may also be "WATCH_TYPE_META". This is a special record type generated
-internally by the watch queue itself. There are two subtypes:
-
- * WATCH_META_REMOVAL_NOTIFICATION
- * WATCH_META_LOSS_NOTIFICATION
-
-The first indicates that an object on which a watch was installed was removed
-or destroyed and the second indicates that some messages have been lost.
-
-"info" indicates a bunch of things, including:
-
- * The length of the message in bytes, including the header (mask with
- WATCH_INFO_LENGTH and shift by WATCH_INFO_LENGTH__SHIFT). This indicates
- the size of the record, which may be between 8 and 127 bytes.
-
- * The watch ID (mask with WATCH_INFO_ID and shift by WATCH_INFO_ID__SHIFT).
- This indicates that caller's ID of the watch, which may be between 0
- and 255. Multiple watches may share a queue, and this provides a means to
- distinguish them.
-
- * A type-specific field (WATCH_INFO_TYPE_INFO). This is set by the
- notification producer to indicate some meaning specific to the type and
- subtype.
-
-Everything in info apart from the length can be used for filtering.
-
-The header can be followed by supplementary information. The format of this is
-at the discretion is defined by the type and subtype.
-
-
-Watch List (Notification Source) API
-====================================
-
-A "watch list" is a list of watchers that are subscribed to a source of
-notifications. A list may be attached to an object (say a key or a superblock)
-or may be global (say for device events). From a userspace perspective, a
-non-global watch list is typically referred to by reference to the object it
-belongs to (such as using KEYCTL_NOTIFY and giving it a key serial number to
-watch that specific key).
-
-To manage a watch list, the following functions are provided:
-
- * ::
-
- void init_watch_list(struct watch_list *wlist,
- void (*release_watch)(struct watch *wlist));
-
- Initialise a watch list. If ``release_watch`` is not NULL, then this
- indicates a function that should be called when the watch_list object is
- destroyed to discard any references the watch list holds on the watched
- object.
-
- * ``void remove_watch_list(struct watch_list *wlist);``
-
- This removes all of the watches subscribed to a watch_list and frees them
- and then destroys the watch_list object itself.
-
-
-Watch Queue (Notification Output) API
-=====================================
-
-A "watch queue" is the buffer allocated by an application that notification
-records will be written into. The workings of this are hidden entirely inside
-of the pipe device driver, but it is necessary to gain a reference to it to set
-a watch. These can be managed with:
-
- * ``struct watch_queue *get_watch_queue(int fd);``
-
- Since watch queues are indicated to the kernel by the fd of the pipe that
- implements the buffer, userspace must hand that fd through a system call.
- This can be used to look up an opaque pointer to the watch queue from the
- system call.
-
- * ``void put_watch_queue(struct watch_queue *wqueue);``
-
- This discards the reference obtained from ``get_watch_queue()``.
-
-
-Watch Subscription API
-======================
-
-A "watch" is a subscription on a watch list, indicating the watch queue, and
-thus the buffer, into which notification records should be written. The watch
-queue object may also carry filtering rules for that object, as set by
-userspace. Some parts of the watch struct can be set by the driver::
-
- struct watch {
- union {
- u32 info_id; /* ID to be OR'd in to info field */
- ...
- };
- void *private; /* Private data for the watched object */
- u64 id; /* Internal identifier */
- ...
- };
-
-The ``info_id`` value should be an 8-bit number obtained from userspace and
-shifted by WATCH_INFO_ID__SHIFT. This is OR'd into the WATCH_INFO_ID field of
-struct watch_notification::info when and if the notification is written into
-the associated watch queue buffer.
-
-The ``private`` field is the driver's data associated with the watch_list and
-is cleaned up by the ``watch_list::release_watch()`` method.
-
-The ``id`` field is the source's ID. Notifications that are posted with a
-different ID are ignored.
-
-The following functions are provided to manage watches:
-
- * ``void init_watch(struct watch *watch, struct watch_queue *wqueue);``
-
- Initialise a watch object, setting its pointer to the watch queue, using
- appropriate barriering to avoid lockdep complaints.
-
- * ``int add_watch_to_object(struct watch *watch, struct watch_list *wlist);``
-
- Subscribe a watch to a watch list (notification source). The
- driver-settable fields in the watch struct must have been set before this
- is called.
-
- * ::
-
- int remove_watch_from_object(struct watch_list *wlist,
- struct watch_queue *wqueue,
- u64 id, false);
-
- Remove a watch from a watch list, where the watch must match the specified
- watch queue (``wqueue``) and object identifier (``id``). A notification
- (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue to
- indicate that the watch got removed.
-
- * ``int remove_watch_from_object(struct watch_list *wlist, NULL, 0, true);``
-
- Remove all the watches from a watch list. It is expected that this will be
- called preparatory to destruction and that the watch list will be
- inaccessible to new watches by this point. A notification
- (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue of each
- subscribed watch to indicate that the watch got removed.
-
-
-Notification Posting API
-========================
-
-To post a notification to watch list so that the subscribed watches can see it,
-the following function should be used::
-
- void post_watch_notification(struct watch_list *wlist,
- struct watch_notification *n,
- const struct cred *cred,
- u64 id);
-
-The notification should be preformatted and a pointer to the header (``n``)
-should be passed in. The notification may be larger than this and the size in
-units of buffer slots is noted in ``n->info & WATCH_INFO_LENGTH``.
-
-The ``cred`` struct indicates the credentials of the source (subject) and is
-passed to the LSMs, such as SELinux, to allow or suppress the recording of the
-note in each individual queue according to the credentials of that queue
-(object).
-
-The ``id`` is the ID of the source object (such as the serial number on a key).
-Only watches that have the same ID set in them will see this notification.
-
-
-Watch Sources
-=============
-
-Any particular buffer can be fed from multiple sources. Sources include:
-
- * WATCH_TYPE_KEY_NOTIFY
-
- Notifications of this type indicate changes to keys and keyrings, including
- the changes of keyring contents or the attributes of keys.
-
- See Documentation/security/keys/core.rst for more information.
-
-
-Event Filtering
-===============
-
-Once a watch queue has been created, a set of filters can be applied to limit
-the events that are received using::
-
- struct watch_notification_filter filter = {
- ...
- };
- ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter)
-
-The filter description is a variable of type::
-
- struct watch_notification_filter {
- __u32 nr_filters;
- __u32 __reserved;
- struct watch_notification_type_filter filters[];
- };
-
-Where "nr_filters" is the number of filters in filters[] and "__reserved"
-should be 0. The "filters" array has elements of the following type::
-
- struct watch_notification_type_filter {
- __u32 type;
- __u32 info_filter;
- __u32 info_mask;
- __u32 subtype_filter[8];
- };
-
-Where:
-
- * ``type`` is the event type to filter for and should be something like
- "WATCH_TYPE_KEY_NOTIFY"
-
- * ``info_filter`` and ``info_mask`` act as a filter on the info field of the
- notification record. The notification is only written into the buffer if::
-
- (watch.info & info_mask) == info_filter
-
- This could be used, for example, to ignore events that are not exactly on
- the watched point in a mount tree.
-
- * ``subtype_filter`` is a bitmask indicating the subtypes that are of
- interest. Bit 0 of subtype_filter[0] corresponds to subtype 0, bit 1 to
- subtype 1, and so on.
-
-If the argument to the ioctl() is NULL, then the filters will be removed and
-all events from the watched sources will come through.
-
-
-Userspace Code Example
-======================
-
-A buffer is created with something like the following::
-
- pipe2(fds, O_TMPFILE);
- ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256);
-
-It can then be set to receive keyring change notifications::
-
- keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
-
-The notifications can then be consumed by something like the following::
-
- static void consumer(int rfd, struct watch_queue_buffer *buf)
- {
- unsigned char buffer[128];
- ssize_t buf_len;
-
- while (buf_len = read(rfd, buffer, sizeof(buffer)),
- buf_len > 0
- ) {
- void *p = buffer;
- void *end = buffer + buf_len;
- while (p < end) {
- union {
- struct watch_notification n;
- unsigned char buf1[128];
- } n;
- size_t largest, len;
-
- largest = end - p;
- if (largest > 128)
- largest = 128;
- memcpy(&n, p, largest);
-
- len = (n->info & WATCH_INFO_LENGTH) >>
- WATCH_INFO_LENGTH__SHIFT;
- if (len == 0 || len > largest)
- return;
-
- switch (n.n.type) {
- case WATCH_TYPE_META:
- got_meta(&n.n);
- case WATCH_TYPE_KEY_NOTIFY:
- saw_key_change(&n.n);
- break;
- }
-
- p += len;
- }
- }
- }