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

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Date:	Thu, 7 Feb 2013 18:34:47 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, criu@...nvz.org,
	linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: Re: [PATCH 3/3] signalfd: add ability to read siginfo-s without
	dequeuing signals (v2)

Andrey, sorry for delay.

As for API, I leave this to you and Michael. Not that I like these
new flags, but I agree that pread() hack was not pretty too.

On 01/29, Andrey Vagin wrote:
> +static ssize_t signalfd_peek(struct signalfd_ctx *ctx,
> +				siginfo_t *info, loff_t *ppos, int queue_mask)
> +{
> +	loff_t seq = *ppos / sizeof(struct signalfd_siginfo);
> +	int signr = 0;
> +
> +	if (queue_mask & SIGQUEUE_PRIVATE)
> +		signr = peek_signal(&current->pending,
> +					&ctx->sigmask, info, &seq);
> +	else if (queue_mask & SIGQUEUE_SHARED)
> +		signr = peek_signal(&current->signal->shared_pending,
> +					 &ctx->sigmask, info, &seq);
> +	(*ppos) += sizeof(struct signalfd_siginfo);

Now that this can work even with normal read(), we will actually change
f_pos. Then perhaps signalfd_fops->llseek() should work too. But this
is minor...

Hmm. but since it works with read(), we shouldn't increment *ppos unless
signalfd_copyinfo() succeeds?

Btw, why do you pass seq by reference? Looks unneeded.

Oleg.

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