linux-kernel - Re: [PATCH 2/3] signalfd: add ability to return siginfo in a raw format (v2)

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Message-ID: <CANaxB-wXdPZFzD3BhkD6niDA6M1NiNrc5coKf9bSx+ar_fZecg@mail.gmail.com>
Date:	Sat, 19 Jan 2013 14:50:12 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	mtk.manpages@...il.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, criu@...nvz.org,
	linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: Re: [PATCH 2/3] signalfd: add ability to return siginfo in a raw
 format (v2)

2013/1/19 Michael Kerrisk (man-pages) <mtk.manpages@...il.com>:
>> As SFD_RAW is being added to the kernel API we should document it.
>> Please keep Michael cc'ed and work with him on getting the manpages
>> updated.
>
> The API is certainly no thing of beauty, as I already remarked here:
> http://thread.gmane.org/gmane.linux.file-systems/70420/focus=1420228

All of us have similar thoughts, but we don't know a better solution.

Here is an example of usage signalfd and pread:
http://lists.openvz.org/pipermail/criu/2013-January/007040.html

>
> A description of the API can be found here:
> https://lwn.net/Articles/531939/

Thanks you for the attempt to involve more people to this discussion.

>
> The main problem is the ugliness of changing the meaning of pread()'s
> 'offset' argument to be a multiplexed [signal queue selector + queue
> position].
>
> I do wonder if we can do better, though I have no particular solution
> to offer beyond the sledgehammer of adding a new system call.

If we are choosing between this interface or a new syscall, I would
prefer this interface. signalfd is a special descriptor, so I think it
is not a big deal, that it works a bit strange. If all other would
decides, that a new syscall is better, I will not ague.

Michael, thank you for the comments.

>
> Cheers,
>
> Michael
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Author of "The Linux Programming Interface"; http://man7.org/tlpi/
> --
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