linux-kernel - Re: SPLICE_F_NONBLOCK semantics...

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Message-ID: <20091002074754.GE14918@kernel.dk>
Date:	Fri, 2 Oct 2009 09:47:54 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	torvalds@...ux-foundation.org, eric.dumazet@...il.com,
	jgunthorpe@...idianresearch.com, vl@...ba.org,
	opurdila@...acom.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: SPLICE_F_NONBLOCK semantics...

On Thu, Oct 01 2009, David Miller wrote:
> From: Linus Torvalds <torvalds@...ux-foundation.org>
> Date: Thu, 1 Oct 2009 15:21:44 -0700 (PDT)
> 
> > On Thu, 1 Oct 2009, David Miller wrote:
> >> 
> >> It depends upon our interpretation of how you intended the
> >> SPLICE_F_NONBLOCK flag to work when you added it way back
> >> when.
> >> 
> >> Linus introduced  SPLICE_F_NONBLOCK in commit 29e350944fdc2dfca102500790d8ad6d6ff4f69d
> >> (splice: add SPLICE_F_NONBLOCK flag )
> >> 
> >>   It doesn't make the splice itself necessarily nonblocking (because the
> >>   actual file descriptors that are spliced from/to may block unless they
> >>   have the O_NONBLOCK flag set), but it makes the splice pipe operations
> >>   nonblocking.
> >> 
> >> Linus intention was clear : let SPLICE_F_NONBLOCK control the splice pipe mode only
> > 
> > Ack. The original intent was for the flag to affect the buffering, not the 
> > end points.
> 
> Great, thanks for reviewing.
> 
> > Although the more I think about it, the more I suspect that the
> > whole NONBLOCK thing should probably have been two bits, and simply
> > been about "nonblocking input" vs "nonblocking output" (so that you
> > could control both sides on a call-by-call basis).
> 
> I think we could still extend things in this way if we wanted to.
> So if you specify the explicit input and/or output nonblock flag,
> it takes precedence over the SPLICE_F_NONBLOCK thing.

Yes I agree, thank god for having a 'flags' parameter for the syscalls
:-). I'll make a note to add and test bidirectional nonblock hints.

The net patch looks fine and correct to me, feel free to add my acked-by
if you want.

-- 
Jens Axboe

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