linux-kernel - Re: [PATCH] epoll: add exclusive wakeups flag

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Message-ID: <CAKgNAkgb-2omfCc=oBr66_CViJjBQ6=3vNfES99m6ZQ7g36p2Q@mail.gmail.com>
Date:	Fri, 11 Mar 2016 21:30:49 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Jason Baron <jbaron@...mai.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Al Viro <viro@....linux.org.uk>,
	Eric Wong <normalperson@...t.net>,
	Madars Vitolins <m@...odev.com>,
	Jonathan Corbet <corbet@....net>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hagen Paul Pfeifer <hagen@...u.net>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] epoll: add exclusive wakeups flag

>> By the way, in the code you have
>>
>>         case EPOLL_CTL_MOD:
>>                 if (epi) {
>>                         if (!(epi->event.events & EPOLLEXCLUSIVE)) {
>>                                 epds.events |= POLLERR | POLLHUP;
>>                                 error = ep_modify(ep, epi, &epds);
>>                         }
>>
>> I think the "if" here is redundant. IIUC, earlier in the code you
>> disallow EPOLL_CTL_MOD with EPOLLEXCLUSIVE.
>>
>> Cheers,
>>
>> Michael
>>
>>
>
> Hi Michael,
>
> So the previous check ensures that you can not add the EPOLLEXCLUSIVE
> flag to the events via an EPOLL_CTL_MOD operation, where EPOLLEXCLUSIVE
> may not be the existing events set. While this check here ensure you
> can't modify an existing set that already has the EPOLLEXCLUSIVE flag.

Hmmm - I misread the code, itr seems :-/. Could you please carefully
check the man page text I sent earlier in this thread. Maybe I
injected some errors into the text.

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/