linux-kernel - Re: Passing epoll file descriptors across Unix domain sockets

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Message-ID: <Pine.LNX.4.64.0802291120000.31028@alien.or.mcafeemobile.com>
Date:	Fri, 29 Feb 2008 11:20:45 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Passing epoll file descriptors across Unix domain sockets

On Fri, 29 Feb 2008, Michael Kerrisk wrote:

> Hi Davide,
> 
> After all of the recent discussions about epoll, I've been reviewing
> other parts of the epoll.7 man page.  In that page there is the
> following:
> 
>        Q5  Can  I  send  the  epoll  file descriptor over a Unix
>            domain socket to another process?
> 
>        A5  No.
> 
> This does not seem accurate.  I can understand that it makes no sense
> to pass a an epoll file descriptor over a Unix domain socket, because
> the receiving process does not have the file descriptors that are in
> the epoll set.
> 
> However, it is indeed possible (no errors result) to pass an epoll fd
> over a Unix doman socket using SCM_RIGHTS.  (I have just now tested
> this.)
> 
> Can you clarify?  I suspect the text should really read:
> 
>        Q5  Can  I  send  an  epoll  file  descriptor over a Unix
>            domain socket to another process?
> 
>        A5  Yes, but it does not make sense to do this, since the
>            receiving  process  would not have copies of the file
>            descriptors in the epoll set.
> 
> Does that seem okay?

Looks okay to me.



- Davide


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