linux-kernel - Re: PROBLEM: epoll_wait() returns wrong events for EOF with EPOLLOUT

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Message-ID: <Pine.LNX.4.64.0607141535070.2463@alien.or.mcafeemobile.com>
Date:	Fri, 14 Jul 2006 15:38:55 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Lindner <mikell@...online.net>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: PROBLEM: epoll_wait() returns wrong events for EOF with EPOLLOUT

On Fri, 14 Jul 2006, Michael Lindner wrote:

> [2.] Full description of the problem/report:
> 	If a program is waiting in epoll_wait() for EPOLLOUT event on a
> 	socket and the socket is closed, epoll_wait() returns EPOLLHUP|EPOLLERR,
> 	but *not* EPOLLOUT.
>
> 	This differs from the expected behavior in several ways:
>
> 	1. epoll_wait is not returning the events it was told to wait for.
> 	    Why not return EPOLLOUT? select() returns an FD as writable on EOF.

Because it is not supposed to.



> 	2. epoll_wait() is returning events it was not told to wait for.

Because they are non-maskeable.



> 	3. EPOLLHUP is not returned if EPOLLIN was requested, why
> 	   do so on EPOLLOUT?

Please take a look at the POSIX docs for poll(2).



> 	Also a minor issue - epoll_ctl doesn't check if the fd in events.data.fd
> 	is the same as the fd that's been passed in as argument 3. If they differ
> 	(due to programmer error), epoll_wait will return an event with the
> 	incorrect events.data.fd specified to epoll_ctl().

That's an opaque union and epoll couldn't care less of the content.



- Davide


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