linux-kernel - Re: [RFC PATCH net-next] tun: support retrieving multiple packets in a single read with IFF_MULTI

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Date:	Mon, 22 Dec 2014 12:18:39 -0800
From:	Alex Gartrell <agartrell@...com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	<jasonwang@...hat.com>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<mst@...hat.com>, <herbert@...dor.apena.org.au>,
	<kernel-team@...com>
Subject: Re: [RFC PATCH net-next] tun: support retrieving multiple packets
 in a single read with IFF_MULTI_READ

Hey Herbert,

Thanks for getting back to me

On 12/22/14 4:09 AM, Herbert Xu wrote:
> As tun already has a socket interface can we do this through
> recvmmsg?

This just presents an easier interface (IMHO) for accomplishing that. 
And I say easier because I was unable how to figure out the recvmmsg way 
to do it.

While fully aware that this makes me look like an idiot, I have to admit 
that I've tried and failed to figure out how to get a socket fd out of 
the tun device.

The regular fd doesn't work (which is obvious when you look at the 
implementation sock_from_file), there's a tun_get_socket function but 
it's only referenced by a single file, and none of the ioctl's jump out 
at me as doing anything to enable this behavior.  Additionally, 
tuntap.txt makes no mention of sockets specifically.

FWIW, I don't feel strongly that IFF_MULTI_READ is the right way to do 
this either.

Thanks,
-- 
Alex Gartrell <agartrell@...com>

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