netdev - Re: [PATCH] sendfile() and UDP socket

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Date:	Sun, 21 Sep 2008 17:44:50 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	johnpol@....mipt.ru
Cc:	johaahn@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] sendfile() and UDP socket

From: Evgeniy Polyakov <johnpol@....mipt.ru>
Date: Mon, 22 Sep 2008 04:21:57 +0400

> On Sun, Sep 21, 2008 at 01:04:58AM -0700, David Miller (davem@...emloft.net) wrote:
> > Applications which work over datagram protocols must perform their own
> > segmentation.  It is not like doing a send over a stream protocol like
> > TCP, where you can use whatever length you want for send calls and
> > segmentation is done for the application.
> 
> But isn't the whole idea of the sendfile() is to send a file no matter
> what underlying media is?

It's a way to fabricate a send() directly from the page cache.

> That's maybe because udp_sendpage() does not support sending pending
> data if new packet is too big to attach?

I don't think so.

It's simply enforcing the wsize/rsize that's configured for the mount.
And this is exactly deciding what the UDP segment size should be.
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