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

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Date:	Wed, 13 Nov 2013 22:44:23 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Amit Pundir <amit.pundir@...aro.org>
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 Wednesday, November 13, 2013 01:35:38 PM Amit Pundir wrote:
> 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.

Well, you can do that too.

> >> 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()?

This particular one doesn't really set anything.  I suppose that a name like
"ep_take_care_of_epollwakeup" might be somewhat closer to what it really does ...

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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