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

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Date:	Fri, 15 Feb 2013 19:53:33 +0000
From:	Pedro Alves <palves@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrey Vagin <avagin@...nvz.org>, 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

On 02/15/2013 07:43 PM, Oleg Nesterov wrote:
> On 02/15, Pedro Alves wrote:
>>
>> Not sure I'm reading the patch right, but it looks like GDB would
>> be able to use this as alternative to PTRACE_GET_SIGINFO variant
> 
> No, it is different. PTRACE_GETSIGINFO reports the siginfo for the signal
> which was already dequeued (ignoring the fact ->last_siginfo != NULL doesn't
> necessarily mean we report a signal), while this patch allows to look at
> the pending signals which were not reported yet.

Ah, I had assumed queue position 0 would be the dequeued signal.

>> I wouldn't mind if this was added unconditionally
>> instead of wrapped on CONFIG_CHECKPOINT_RESTORE.
> 
> I agree. If you think gdb can use this new feature,  CONFIG_ can go away.

I think so -- we can add a gdb command to dump the list of
pending signals, which I think is something that'd be useful.

> 
>> 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.

-- 
Pedro Alves

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