netdev - Re: SPLICE_F_NONBLOCK semantics...

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Date:	Thu, 01 Oct 2009 15:27:17 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	torvalds@...ux-foundation.org
Cc:	eric.dumazet@...il.com, jgunthorpe@...idianresearch.com,
	vl@...ba.org, opurdila@...acom.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: SPLICE_F_NONBLOCK semantics...

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.

Anyways, just an idea.
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