lkml.org 
[lkml]   [2011]   [Jul]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH] poll: add poll_requested_events() function
On Fri, 1 Jul 2011 15:37:30 +0200
Hans Verkuil <hverkuil@xs4all.nl> wrote:

> In some cases the poll() implementation in a driver has to do different
> things depending on the events the caller wants to poll for. An example is
> when a driver needs to start a DMA engine if the caller polls for POLLIN,
> but doesn't want to do that if POLLIN is not requested but instead only
> POLLOUT or POLLPRI is requested. This is something that can happen in the
> video4linux subsystem.

The change makes sense to me, FWIW. One bit of trivia I noticed while
looking at it:

> @@ -796,7 +792,7 @@ static int do_poll(unsigned int nfds, struct poll_list *list,
> * All waiters have already been registered, so don't provide
> * a poll_table to them on the next loop iteration.
> */
> - pt = NULL;
> + pt->qproc = NULL;
> if (!count) {
> count = wait->error;
> if (signal_pending(current))

The comment at the beginning of this hunk is no longer accurate since the
poll_table is, indeed, still being supplied. The previous comment in the
same function:

/*
* Fish for events. If we found one, record it
* and kill the poll_table, so we don't
* needlessly register any other waiters after
* this. They'll get immediately deregistered
* when we break out and return.
*/

Could also use tweaking.

jon


\
 
 \ /
  Last update: 2011-07-07 18:45    [W:0.032 / U:0.496 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site