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pipe: Add notification lossage handling

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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: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells
2020-01-14 17:07:12 +00:00
parent 8cfba76383
commit e7d553d69c
4 changed files with 40 additions and 0 deletions
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28
fs/pipe.c
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@@ -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);