netdev - Re: [RFC v2] mac80211: assign needed

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Date:	Mon, 05 May 2008 21:05:15 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	David Miller <davem@...emloft.net>
Cc:	tomasw@...il.com, linville@...driver.com, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org
Subject: Re: [RFC v2] mac80211: assign needed_headroom/tailroom for netdevs

On Mon, 2008-05-05 at 11:58 -0700, David Miller wrote:
> From: Johannes Berg <johannes@...solutions.net>
> Date: Mon, 05 May 2008 19:57:34 +0200
> 
> > NETIF_F_FRAGLIST I haven't understood, but it seems to apply mostly for
> > IP fragmentation?
> 
> That's right.  It's for cards that can do IP fragmentation in
> hardware.

What does "do IP fragmentation in hardware" mean?

ip_output.c says:

 *      This IP datagram is too large to be sent in one piece.  Break it up into
 *      smaller pieces (each of size equal to IP header plus
 *      a block of the data of the original IP data part) that will yet fit in a
 *      single device frame, and queue such a frame for sending.

and later

                        /* Prepare header of the next frame,
                         * before previous one went down. */

so that seems to indicate that if the hardware just sends it all out in
the right order it'll be fine.

So the point is that the hardware will have to split it up into ethernet
frames on the IP boundaries?

johannes

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