linux-kernel - Re: [CRIU] [PATCH 3/3] signalfd: add ability to read siginfo-s without dequeuing signals (v2)

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Date:	Mon, 11 Feb 2013 18:53:11 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
CC:	Andrew Vagin <avagin@...allels.com>, mtk.manpages@...il.com,
	David Howells <dhowells@...hat.com>, linux-api@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	criu@...nvz.org, Cyrill Gorcunov <gorcunov@...nvz.org>,
	Andrey Wagin <avagin@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Dave Jones <davej@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [CRIU] [PATCH 3/3] signalfd: add ability to read siginfo-s without
 dequeuing signals (v2)

On 02/11/2013 06:46 PM, Denys Vlasenko wrote:
> On Mon, Feb 11, 2013 at 11:59 AM, Andrew Vagin <avagin@...allels.com> wrote:
>>>> I suppose I had wondered along similar lines, but in a slightly
>>>> different direction: would the use of a /proc interface to get the
>>>> queued signals make some sense?
>>>
>>> I think that /proc interface beats adding magic flags and magic semantic
>>> to [p]read.
>>>
>>> It also has the benefit of being human-readable. You don't need
>>> to write a special C program to "cat /proc/$$/foo".
>>>
>>> Andrey, I know that it is hard to let go of the code you invested time
>>> and efforts in creating. But this isn't the last patch, is it?
>>> You will need to retrieve yet more data for process checkpointing.
>>> When you start working on the next patch for it, consider trying
>>> /proc approach.
>>
>> I don't think that we need to convert siginfo into a human readable format
>> in kernel.
> 
> My point is that bolting hacks onto various bits of kernel API
> in order to support process checkpointing makes those APIs
> (their in-kernel implementation) ridden with special cases
> and harder to support in the future.
> 
> Process checkpointing needs to bite the bullet and
> create its own API instead.

This is bad approach as well. What we should do is come up with a sane
API that makes sense without the checkpoint-restore project _when_ _possible_.

> Whether it would be a /proc/PID/checkpoint or a
> ptrace(PTRACE_GET_CHKPOINT_DATA) is another question.

Thanks,
Pavel
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