linux-kernel - Re: [PATCH 1/4] signalfd: add ability to return siginfo in a raw format

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Message-ID: <20121225165803.GA9066@redhat.com>
Date:	Tue, 25 Dec 2012 17:58:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Andrey Wagin <avagin@...il.com>, linux-kernel@...r.kernel.org,
	criu@...nvz.org, linux-fsdevel@...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>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: Re: [PATCH 1/4] signalfd: add ability to return siginfo in a raw
	format

On 12/25, Pavel Emelyanov wrote:
>
> On 12/25/2012 07:27 PM, Oleg Nesterov wrote:
> >
> > I guess that probably you actually need DUMP, not DEQUEUE. but the
> > latter is not trivial. However, perhaps we can do this assuming that
> > all other threads are sleeping and nobody can do dequeue_signal().
> > Say, we can play with ppos/llseek. If *ppos is not zero,
> > signalfd_dequeue() could dump the nth entry from list or return 0.
>
> This would be perfect, but isn't it better to preserve the pos
> semantics -- we do know size of entry we're about to copy, we can
> treat pos as offset in bytes, not in elements.

nr-of-records looks better (more flexible) than nr-of-bytes to me. And
perhaps we can also encode private-or-shared into ppos. But I will not
argue in any case.

Oleg.

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