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 15:46:52 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andrew Vagin <avagin@...allels.com>
Cc:	mtk.manpages@...il.com, David Howells <dhowells@...hat.com>,
	Pavel Emelyanov <xemul@...allels.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 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.

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

-- 
vda
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