linux-kernel - Re: [RFC][PATCH v2] epoll: allow EPOLLWAKEUP flag if PM

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Date:	Wed, 13 Nov 2013 13:35:38 +0530
From:	Amit Pundir <amit.pundir@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	John Stultz <john.stultz@...aro.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RFC][PATCH v2] epoll: allow EPOLLWAKEUP flag if PM_SLEEP is enabled

On 13 November 2013 05:29, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, November 13, 2013 02:22:28 AM Amit Pundir wrote:
>> ep_create_wakeup_source() reports ENOMEM
>
> That needs to be fixed too.  I suppose we can make the wakeup_source_register()
> stub for CONFIG_PM_SLEEP unset return ERR_PTR(-ENOSYS) or something like that
> and ep_create_wakeup_source() return that instead of -ENOMEM.  It looks like
> eventpoll.c is the only user of it built for CONFIG_PM_SLEEP unset, but that
> needs to be double checked.

Instead of modifying wakeup_source_register() stub, what if I make
ep_create_wakeup_source() static inline as well and use its stub to
return -ENOSYS when CONFIG_PM_SLEEP is not set?
ep_create_wakeup_source() is used only in fs/eventpoll.c anyway.

>
>> if wakeup_source_register()
>> returns NULL. ep_create_wakeup_source() assumes that NULL is only
>> returned if we run into ENOMEM but NULL is also returned when
>> CONFIG_PM_SLEEP is disabled.
>>
>> Signed-off-by: Amit Pundir <amit.pundir@...aro.org>
>> ---
>> Changed in v2:
>> Using static inline functions instead of #ifdefs
>> ---
>>  fs/eventpoll.c                 |    3 +--
>>  include/uapi/linux/eventpoll.h |   12 ++++++++++++
>>  2 files changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
>> index 473e09d..10f9c43 100644
>> --- a/fs/eventpoll.c
>> +++ b/fs/eventpoll.c
>> @@ -1820,8 +1820,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
>>               goto error_tgt_fput;
>>
>>       /* Check if EPOLLWAKEUP is allowed */
>> -     if ((epds.events & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND))
>> -             epds.events &= ~EPOLLWAKEUP;
>> +     ep_epollwakeup_check(&epds.events);
>
> The "check" part of the name kind of suggests that the function will not change
> things.  What about ep_adjust_epollwakeup() or something along these lines?

I see couple of ep_set_* functions in eventpoll.c. Does it make sense
to have something like ep_set_epollwakeup()?

>
> And why don't you pass a pointer to epds to it?  Wouldn't it be cleaner this way?

Ok.

Regards,
Amit Pundir

>
>>
>>       /*
>>        * We have to check that the file structure underneath the file descriptor
>> diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
>> index 2c267bc..1d139c2 100644
>> --- a/include/uapi/linux/eventpoll.h
>> +++ b/include/uapi/linux/eventpoll.h
>> @@ -62,4 +62,16 @@ struct epoll_event {
>>  } EPOLL_PACKED;
>>
>>
>> +#ifdef CONFIG_PM_SLEEP
>> +static inline void ep_epollwakeup_check(__u32 *epev)
>> +{
>> +     if ((*epev & EPOLLWAKEUP) && !capable(CAP_BLOCK_SUSPEND))
>> +             *epev &= ~EPOLLWAKEUP;
>> +}
>> +#else
>> +static inline void ep_epollwakeup_check(__u32 *epev)
>> +{
>> +     *epev &= ~EPOLLWAKEUP;
>> +}
>> +#endif
>>  #endif /* _UAPI_LINUX_EVENTPOLL_H */
>
> Thanks!
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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