Re: [RFC][PATCH] fix short copy handling in copy_mc_pipe_to_iter()

[David Howells]

Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:

> What's wrong with
>         p_occupancy = pipe_occupancy(head, tail);
>         if (p_occupancy >= pipe->max_usage)
>                 return 0;
> 	else
> 		return pipe->max_usage - p_occupancy;

Because "pipe->max_usage - p_occupancy" can be negative.

post_one_notification() is limited by pipe->ring_size, not pipe->max_usage.

The idea is to allow some slack in a watch pipe for the watch_queue code to
use that userspace can't.

David