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Message-ID: <alpine.LFD.2.01.0910011516390.6996@localhost.localdomain>
Date: Thu, 1 Oct 2009 15:21:44 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: David Miller <davem@...emloft.net>
cc: eric.dumazet@...il.com, jgunthorpe@...idianresearch.com,
vl@...ba.org, opurdila@...acom.com, netdev@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Jens Axboe <jens.axboe@...cle.com>
Subject: Re: SPLICE_F_NONBLOCK semantics...
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.
> splice(socket,0,pipe,0,128*1024,SPLICE_F_MOVE | SPLICE_F_NONBLOCK );
>
> to block on data coming from socket (if file is in blocking mode),
> and not block on pipe output (to avoid deadlock)
Yes. Sounds correct. 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).
But I think that your patch is fundamentally correct with the semantics
as-is.
Linus
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