Commit 8cfba763 authored by David Howells's avatar David Howells
Browse files

pipe: Allow buffers to be marked read-whole-or-error for notifications 



Allow a buffer to be marked such that read() must return the entire buffer
in one go or return ENOBUFS.  Multiple buffers can be amalgamated into a
single read, but a short read will occur if the next "whole" buffer won't
fit.

This is useful for watch queue notifications to make sure we don't split a
notification across multiple reads, especially given that we need to
fabricate an overrun record under some circumstances - and that isn't in
the buffers.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
parent f5b5a164

fs/pipe.c

+7 −1
Original line number Diff line number Diff line
@@ -320,8 +320,14 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) 
			size_t written;

			int error;



			if (chars > total_len)

			if (chars > total_len) {

				if (buf->flags & PIPE_BUF_FLAG_WHOLE) {

					if (ret == 0)

						ret = -ENOBUFS;

					break;

				}

				chars = total_len;

			}



			error = pipe_buf_confirm(pipe, buf);

			if (error) {

include/linux/pipe_fs_i.h

+1 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#define PIPE_BUF_FLAG_ATOMIC	0x02	/* was atomically mapped */

#define PIPE_BUF_FLAG_GIFT	0x04	/* page is a gift */

#define PIPE_BUF_FLAG_PACKET	0x08	/* read() as a packet */

#define PIPE_BUF_FLAG_WHOLE	0x10	/* read() must return entire buffer or error */



/**

 *	struct pipe_buffer - a linux kernel pipe buffer

kernel/watch_queue.c

+1 −1
Original line number Diff line number Diff line
@@ -115,7 +115,7 @@ static bool post_one_notification(struct watch_queue *wqueue, 
	buf->ops = &watch_queue_pipe_buf_ops;

	buf->offset = offset;

	buf->len = len;

	buf->flags = 0;

	buf->flags = PIPE_BUF_FLAG_WHOLE;

	pipe->head = head + 1;



	if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {

samples/watch_queue/watch_test.c

+1 −1
Original line number Diff line number Diff line
@@ -63,7 +63,7 @@ static void saw_key_change(struct watch_notification *n, size_t len) 
 */

static void consumer(int fd)

{

	unsigned char buffer[4096], *p, *end;

	unsigned char buffer[433], *p, *end;

	union {

		struct watch_notification n;

		unsigned char buf1[128];

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