netdev - Re: Splice on blocking TCP sockets again..

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Message-ID: <4AC2F3E4.5000904@gmail.com>
Date:	Wed, 30 Sep 2009 08:00:04 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Volker Lendecke <vl@...ba.org>
Subject: Re: Splice on blocking TCP sockets again..

Eric Dumazet a écrit :
> Jason Gunthorpe a écrit :
>>> One way to handle this is to switch tcp_read() to use the underlying file O_NONBLOCK
>>> flag, as other socket operations do. And let SPLICE_F_NONBLOCK control the pipe output only.
> 
> arg, this was tcp_splice_read() of course
> 
>> Thanks Eric, this seems reasonable from my userspace perspective.
>>
>> I admit I don't understand why SPLICE_F_NONBLOCK exists, it seems very
>> un-unixy to have a syscall completely ignore the NONBLOCK flag of the
>> fd it is called on. Ie setting NONBLOCK on the pipe itself does
>> nothing when using splice..
>>
> 
> Hmm, good question, I dont have the answer but I'll digg one.
> 

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.

Signed-off-by: Linus Torvalds <torvalds@...l.org>


See Linus intention was pretty clear : O_NONBLOCK should be taken into account
by 'actual file that are spliced from/to', regardless of SPLICE_F_NONBLOCK flag

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