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.

David Howells committed 6 years ago

Commit e7d553d1 parent 8cfba764 files · +40 −0Browse files

Unified · Split

4 files

fs/pipe.c +28 −0
include/linux/pipe_fs_i.h +7 −0
kernel/watch_queue.c +2 −0
samples/watch_queue/watch_test.c +3 −0

fs/pipe.c+28−0

@@ -314,6 +314,30 @@ pipe_read(struct kiocb iocb, struct iov_iter to) · 313 unmodified lines
314	314	unsigned int tail = pipe->tail;
315	315	unsigned int mask = pipe->ring_size - 1;
316	316
	317	+#ifdef CONFIG_WATCH_QUEUE
	318	+ if (pipe->note_loss) {
	319	+ struct watch_notification n;
	320	+
	321	+ if (total_len < 8) {
	322	+ if (ret == 0)
	323	+ ret = -ENOBUFS;
	324	+ break;
	325	+ }
	326	+
	327	+ n.type = WATCH_TYPE_META;
	328	+ n.subtype = WATCH_META_LOSS_NOTIFICATION;
	329	+ n.info = watch_sizeof(n);
	330	+ if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {
	331	+ if (ret == 0)
	332	+ ret = -EFAULT;
	333	+ break;
	334	+ }
	335	+ ret += sizeof(n);
	336	+ total_len -= sizeof(n);
	337	+ pipe->note_loss = false;
	338	+ }
	339	+#endif
	340	+
317	341	if (!pipe_empty(head, tail)) {
318	342	struct pipe_buffer *buf = &pipe->bufs[tail & mask];
319	343	size_t chars = buf->len;
@@ -355,6 +379,10 @@ pipe_read(struct kiocb iocb, struct iov_iter to) · 35 unmodified lines
355	379	if (!buf->len) {
356	380	pipe_buf_release(pipe, buf);
357	381	spin_lock_irq(&pipe->rd_wait.lock);
	382	+#ifdef CONFIG_WATCH_QUEUE
	383	+ if (buf->flags & PIPE_BUF_FLAG_LOSS)
	384	+ pipe->note_loss = true;
	385	+#endif
358	386	tail++;
359	387	pipe->tail = tail;
360	388	spin_unlock_irq(&pipe->rd_wait.lock);

include/linux/pipe_fs_i.h+7−0

@@ -9,6 +9,9 @@ · 8 unmodified lines
9	9	#define PIPE_BUF_FLAG_GIFT 0x04 /* page is a gift */
10	10	#define PIPE_BUF_FLAG_PACKET 0x08 /* read() as a packet */
11	11	#define PIPE_BUF_FLAG_WHOLE 0x10 /* read() must return entire buffer or error */
	12	+#ifdef CONFIG_WATCH_QUEUE
	13	+#define PIPE_BUF_FLAG_LOSS 0x20 /* Message loss happened after this buffer */
	14	+#endif
12	15
13	16	/**
14	17	* struct pipe_buffer - a linux kernel pipe buffer
@@ -34,6 +37,7 @@ struct pipe_buffer { · 19 unmodified lines
34	37	* @wr_wait: writer wait point in case of full pipe
35	38	* @head: The point of buffer production
36	39	* @tail: The point of buffer consumption
	40	+ * @note_loss: The next read() should insert a data-lost message
37	41	* @max_usage: The maximum number of slots that may be used in the ring
38	42	* @ring_size: total number of buffers (should be a power of 2)
39	43	* @nr_accounted: The amount this pipe accounts for in user->pipe_bufs
@@ -56,6 +60,9 @@ struct pipe_inode_info { · 16 unmodified lines
56	60	unsigned int tail;
57	61	unsigned int max_usage;
58	62	unsigned int ring_size;
	63	+#ifdef CONFIG_WATCH_QUEUE
	64	+ bool note_loss;
	65	+#endif
59	66	unsigned int nr_accounted;
60	67	unsigned int readers;
61	68	unsigned int writers;

kernel/watch_queue.c+2−0

@@ -132,6 +132,8 @@ out: · 131 unmodified lines
132	132	return done;
133	133
134	134	lost:
	135	+ buf = &pipe->bufs[(head - 1) & mask];
	136	+ buf->flags \|= PIPE_BUF_FLAG_LOSS;
135	137	goto out;
136	138	}
137	139

samples/watch_queue/watch_test.c+3−0

@@ -120,6 +120,9 @@ static void consumer(int fd) · 119 unmodified lines
120	120	(n.n.info & WATCH_INFO_ID) >>
121	121	WATCH_INFO_ID__SHIFT);
122	122	break;
	123	+ case WATCH_META_LOSS_NOTIFICATION:
	124	+ printf("-- LOSS --\n");
	125	+ break;
123	126	default:
124	127	printf("other meta record\n");
125	128	break;