linux-kernel - RE: sendfile to nonblocking socket

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Date:	Mon, 23 Apr 2007 15:52:58 -0700
From:	"David Schwartz" <davids@...master.com>
To:	<linux-kernel@...r.kernel.org>
Subject: RE: sendfile to nonblocking socket


> As I see, nonblocking mode is enabled - sendfile sends less than asked.  
> But 2G via single 30 seconds sendfile call - this is blocking call. How 
> can I  avoid that?  I prefer sendfile as fastest way to send file 
> content to network socket. The problem with sendfile block on 
> nonblocking socket has place only when I'm using network connection, 
> that is faster than my hard disk, for example  gigabit NIC or localhost. 
> When I use 100Mbit NIC, which is slower, than my hard disk,  I got small 
> and fast sendfile calls without blocking.
> 
> My kernel is  Linux 2.6.20.3-grsec x86_64. I verified that also on 
> 2.6.18 - same results. Please advise.

You have a misunderstanding about the semantics of 'sendfile'. The 'sendfile' function is just a more efficient version of a read followed by a write. If you did a read followed by a write, it would block as well (in the read).

DS


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