Commit e7d553d6 authored by David Howells's avatar David Howells
Browse files

pipe: Add notification lossage handling 



Add handling for loss of notifications by having read() insert a
loss-notification message after it has read the pipe buffer that was last
in the ring when the loss occurred.

Lossage can come about either by running out of notification descriptors or
by running out of space in the pipe ring.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
parent 8cfba763

fs/pipe.c

+28 −0
Original line number Diff line number Diff line
@@ -314,6 +314,30 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) 
		unsigned int tail = pipe->tail;

		unsigned int mask = pipe->ring_size - 1;



#ifdef CONFIG_WATCH_QUEUE

		if (pipe->note_loss) {

			struct watch_notification n;



			if (total_len < 8) {

				if (ret == 0)

					ret = -ENOBUFS;

				break;

			}



			n.type = WATCH_TYPE_META;

			n.subtype = WATCH_META_LOSS_NOTIFICATION;

			n.info = watch_sizeof(n);

			if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {

				if (ret == 0)

					ret = -EFAULT;

				break;

			}

			ret += sizeof(n);

			total_len -= sizeof(n);

			pipe->note_loss = false;

		}

#endif



		if (!pipe_empty(head, tail)) {

			struct pipe_buffer *buf = &pipe->bufs[tail & mask];

			size_t chars = buf->len;
@@ -355,6 +379,10 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to) 
			if (!buf->len) {

				pipe_buf_release(pipe, buf);

				spin_lock_irq(&pipe->rd_wait.lock);

#ifdef CONFIG_WATCH_QUEUE

				if (buf->flags & PIPE_BUF_FLAG_LOSS)

					pipe->note_loss = true;

#endif

				tail++;

				pipe->tail = tail;

				spin_unlock_irq(&pipe->rd_wait.lock);

include/linux/pipe_fs_i.h

+7 −0
Original line number Diff line number Diff line
@@ -9,6 +9,9 @@ 
#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 */

#ifdef CONFIG_WATCH_QUEUE

#define PIPE_BUF_FLAG_LOSS	0x20	/* Message loss happened after this buffer */

#endif



/**

 *	struct pipe_buffer - a linux kernel pipe buffer
@@ -34,6 +37,7 @@ 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
@@ -56,6 +60,9 @@ 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;

kernel/watch_queue.c

+2 −0
Original line number Diff line number Diff line
@@ -132,6 +132,8 @@ out: 
	return done;



lost:

	buf = &pipe->bufs[(head - 1) & mask];

	buf->flags |= PIPE_BUF_FLAG_LOSS;

	goto out;

}

samples/watch_queue/watch_test.c

+3 −0
Original line number Diff line number Diff line
@@ -120,6 +120,9 @@ static void consumer(int fd) 
					       (n.n.info & WATCH_INFO_ID) >>

					       WATCH_INFO_ID__SHIFT);

					break;

				case WATCH_META_LOSS_NOTIFICATION:

					printf("-- LOSS --\n");

					break;

				default:

					printf("other meta record\n");

					break;

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