linux-kernel - Re: [PATCH] ptrace: add ability to retrieve signals without removing them from a queue

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Date:	Tue, 19 Feb 2013 13:39:42 +0400
From:	Andrey Wagin <avagin@...il.com>
To:	Pedro Alves <palves@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	criu@...nvz.org, linux-api@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] ptrace: add ability to retrieve signals without removing
 them from a queue

2013/2/16 Pedro Alves <palves@...hat.com>:
> Forgot to reply to this bit:
>
> On 02/15/2013 07:43 PM, Oleg Nesterov wrote:
>>> We'd miss the poke
>>> > variant, but that looks like something that could be always be added
>>> > later.
>> Yes. _POKE_ or _QUEUE_ or _DEQUEUE_, we can add more features if user-
>> space wants them.
>
> In general, IMO, I agree with Roland at https://lkml.org/lkml/2002/12/20/84
> in that it's good to have setters for completeness, so that you can
> change all the state via ptrace that you can read via ptrace.
>
> But I'm not doing any of this work, hence my "could always be
> added later" comment instead of actually requesting it.  But if
> we had it, we could make e.g., gdb inspect the signal queues,
> and then be able to tweak a realtime signal before it is
> delivered.

PTRACE_POKESIGINFO is more complicated than PTRACE_PEEKSIGINFO.
Looks like PTRACE_POKESIGINFO should replace a siginfo with the
specified sequence number. Should it be able to change signo? If it is
able, what to do with signalfd, which already got a notification about
the previous signal?..

My opinion is that it "could always be added later", when we will
understand what exactly we want to have.

>
> --
> Pedro Alves
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