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