2 Commits

Author	SHA1	Message	Date
Mauro Carvalho Chehab	50f32634f8	docs: watch_queue: fix some warnings ... Fix those warnings: Documentation/watch_queue.rst:108: WARNING: Inline literal start-string without end-string. Documentation/watch_queue.rst:108: WARNING: Inline emphasis start-string without end-string. Documentation/watch_queue.rst:108: WARNING: Inline emphasis start-string without end-string. Documentation/watch_queue.rst:108: WARNING: Inline emphasis start-string without end-string. Documentation/watch_queue.rst:185: WARNING: Inline literal start-string without end-string. Documentation/watch_queue.rst:185: WARNING: Inline emphasis start-string without end-string. Documentation/watch_queue.rst:184: WARNING: Inline emphasis start-string without end-string. The problem here is that the ``notation`` doesn't accept multi lines. So, replace it to a code block using: :: notation Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/42706310c09a6b4588a1a41078207246ad1238fa.1599660067.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>	2020-09-10 10:48:56 -06:00
David Howells	c73be61ced	pipe: Add general notification queue support ... Make it possible to have a general notification queue built on top of a standard pipe. Notifications are 'spliced' into the pipe and then read out. splice(), vmsplice() and sendfile() are forbidden on pipes used for notifications as post_one_notification() cannot take pipe->mutex. This means that notifications could be posted in between individual pipe buffers, making iov_iter_revert() difficult to effect. The way the notification queue is used is: (1) An application opens a pipe with a special flag and indicates the number of messages it wishes to be able to queue at once (this can only be set once): pipe2(fds, O_NOTIFICATION_PIPE); ioctl(fds[0], IOC_WATCH_QUEUE_SET_SIZE, queue_depth); (2) The application then uses poll() and read() as normal to extract data from the pipe. read() will return multiple notifications if the buffer is big enough, but it will not split a notification across buffers - rather it will return a short read or EMSGSIZE. Notification messages include a length in the header so that the caller can split them up. Each message has a header that describes it: struct watch_notification { __u32 type:24; __u32 subtype:8; __u32 info; }; The type indicates the source (eg. mount tree changes, superblock events, keyring changes, block layer events) and the subtype indicates the event type (eg. mount, unmount; EIO, EDQUOT; link, unlink). The info field indicates a number of things, including the entry length, an ID assigned to a watchpoint contributing to this buffer and type-specific flags. Supplementary data, such as the key ID that generated an event, can be attached in additional slots. The maximum message size is 127 bytes. Messages may not be padded or aligned, so there is no guarantee, for example, that the notification type will be on a 4-byte bounary. Signed-off-by: David Howells <dhowells@redhat.com>	2020-05-19 15:08:24 +01:00