[RFC PATCH 08/14] pipe: Allow buffers to be marked read-whole-or-error for notifications [ver #2]

[Andy Lutomirski]

On Thu, Nov 7, 2019 at 5:39 AM David Howells <dhowells at redhat.com> wrote:
>
> Allow a buffer to be marked such that read() must return the entire buffer
> in one go or return ENOBUFS.  Multiple buffers can be amalgamated into a
> single read, but a short read will occur if the next "whole" buffer won't
> fit.
>
> This is useful for watch queue notifications to make sure we don't split a
> notification across multiple reads, especially given that we need to
> fabricate an overrun record under some circumstances - and that isn't in
> the buffers.

Hmm.  I'm not totally in love with introducing a new error code like
this for read(), especially if it could affect the kind of pipe that
is bound to a file in a filesystem.  But maybe it's not a problem.