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path: root/include/linux/watch_queue.h
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2020-10-01pipe: Fix memory leaks in create_pipe_files()Qian Cai1-0/+6
Calling pipe2() with O_NOTIFICATION_PIPE could results in memory leaks unless watch_queue_init() is successful. In case of watch_queue_init() failure in pipe2() we are left with inode and pipe_inode_info instances that need to be freed. That failure exit has been introduced in commit c73be61cede5 ("pipe: Add general notification queue support") and its handling should've been identical to nearby treatment of alloc_file_pseudo() failures - it is dealing with the same situation. As it is, the mainline kernel leaks in that case. Another problem is that CONFIG_WATCH_QUEUE and !CONFIG_WATCH_QUEUE cases are treated differently (and the former leaks just pipe_inode_info, the latter - both pipe_inode_info and inode). Fixed by providing a dummy wacth_queue_init() in !CONFIG_WATCH_QUEUE case and by having failures of wacth_queue_init() handled the same way we handle alloc_file_pseudo() ones. Fixes: c73be61cede5 ("pipe: Add general notification queue support") Signed-off-by: Qian Cai <cai@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2020-05-19pipe: Add general notification queue supportDavid Howells1-0/+127
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>