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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


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