linux-kernel - Re: signalfd() semantics after execve()

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Date:	Sat, 14 Jul 2007 11:53:35 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk-manpages@....net>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: signalfd() semantics after execve()

On Sat, 14 Jul 2007, Michael Kerrisk wrote:

> Davide, 
> 
> I'm working on the signalfd(2) man page, and I've come
> acorss some puzzling behaviour...  
> 
> What are the intended semantics of a signalfd file descriptor
> after an execve()?
> 
> As far as I can work out, after an execve() the file descriptor
> is still available, but reads from it always return 0, even if:
> 
> a) there were signals pending before the execve().
>    However, sigpending() shows the signal as pending,
>    and the signal can be accepted using sigwaitinfo().
> 
> b) we generate a signal after the execve().
>  
> Is this intended behavior (the "orphaned sighand" condition
> mentioned in the draft man page you sent me?)?  Is it a bug?

It is the intended behaviour. Just like reading from a socket where the 
remote peer disconnected. A return 0 from a read from a signalfd should be 
interpreted as the "virtual connection" with the signal source has been 
dropped.



- Davide


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