Re: [PATCH] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready

Arve Hjønnevåg
2012-07-16T22:04:31Z

On Mon, Jul 16, 2012 at 4:00 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> On Monday, July 16, 2012, Michael Kerrisk wrote:
>> Arve, Rafael,
>>
>> On Tue, May 1, 2012 at 7:33 AM, Arve Hjønnevåg <arve@android.com> wrote:
>> > When an epoll_event, that has the EPOLLWAKEUP flag set, is ready, a
>> > wakeup_source will be active to prevent suspend. This can be used to
>> > handle wakeup events from a driver that support poll, e.g. input, if
>> > that driver wakes up the waitqueue passed to epoll before allowing
>> > suspend.
>>
>> It's late it the -rc series,
>
> Well, exactly. :-)
>
>> but it strikes me that CAP_EPOLLWAKEUP is
>> a poor name for the capability that governs the use of EPOLLWAKEUP.
>> While on the one hand some capabilities are overloaded
>> (https://lwn.net/Articles/486306/), on the other hand we should avoid
>> adding individual capabilities for each new API feature (otherwise
>> capabilities become administratively unwieldy).
>>
>> This capability is not really about "EPOLL". It's about the ability to
>> block system suspend. Therefore, IMO, a better name would be something
>> like: CAP_BLOCK_SUSPEND. This name is better because there might be
>> some other API feature that is later added that also has the effect of
>> preventing system suspends, and we could reasonably govern that
>> feature with the same capability.

We already have another api, "/sys/power/wake_lock", that allow
user-space to block suspend. Do we want to apply this capability that
api as well, or only to apis that do not have other ways to restrict
access?

>>
>> Does that seem sensible to you? I can send a patch for the name change.
>
> I'm not sure what Arve thinks about that, but I'd be fine with that.
>
> Arve, what do you think?
>

CAP_BLOCK_SUSPEND is fine with me, but if it does not apply to the
sysfs interface, then the comment should probably mention this.

--
Arve Hjønnevåg