linux-kernel - Re: [PATCH 0/3] epoll: Add epoll

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Date:	Fri, 9 Jan 2015 09:52:48 +0800
From:	Fam Zheng <famz@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Miklos Szeredi <mszeredi@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>, Zach Brown <zab@...bo.net>,
	David Drysdale <drysdale@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Dario Faggioli <raistlin@...ux.it>,
	"Theodore Ts'o" <tytso@....edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Mike Frysinger <vapier@...too.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Oleg Nesterov <oleg@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Fabian Frederick <fabf@...net.be>,
	Josh Triplett <josh@...htriplett.org>,
	"David S. Miller" <davem@...emloft.net>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 0/3] epoll: Add epoll_pwait1 syscall

On Thu, 01/08 17:28, Andy Lutomirski wrote:
> On Thu, Jan 8, 2015 at 5:25 PM, Fam Zheng <famz@...hat.com> wrote:
> > On Thu, 01/08 09:57, Andy Lutomirski wrote:
> >> I'd like to see a more ambitious change, since the timer isn't the
> >> only problem like this.  Specifically, I'd like a syscall that does a
> >> list of epoll-related things and then waits.  The list of things could
> >> include, at least:
> >>
> >>  - EPOLL_CTL_MOD actions: level-triggered epoll users are likely to
> >> want to turn on and off their requests for events on a somewhat
> >> regular basis.
> >
> > This sounds good to me.
> >
> >>
> >>  - timerfd_settime actions: this allows a single syscall to wait and
> >> adjust *both* monotonic and real-time wakeups.
> >
> > I'm not sure, doesn't this break orthogonality between epoll and timerfd?
> 
> Yes.  It's not very elegant, and more elegant ideas are welcome.

What is the purpose of embedding timerfd operation here? Modifying timerfd
for each poll doesn't sound a common pattern to me.

> 
> >
> >>
> >> Would this make sense?  It could look like:
> >>
> >> int epoll_mod_and_pwait(int epfd,
> >>   struct epoll_event *events, int maxevents,
> >>   struct epoll_command *commands, int ncommands,
> >>   const sigset_t *sigmask);
> >
> > What about flags?
> >
> 
> No room.  Maybe it should just be a struct for everything instead of
> separate args.

Also no room for timeout. A single struct sounds the only way to go.

Fam
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