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: David Howells <dhowells@redhat.com>
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index ad64ea30..9a9699c 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -132,6 +132,8 @@ static bool post_one_notification(struct watch_queue *wqueue,
return done;
lost:
+ buf = &pipe->bufs[(head - 1) & mask];
+ buf->flags |= PIPE_BUF_FLAG_LOSS;
goto out;
}