linux-kernel - Re: alloc skb based on a given data buffer

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Message-Id: <1253005050.7549.58.camel@debian>
Date:	Tue, 15 Sep 2009 16:57:29 +0800
From:	Zhu Yi <yi.zhu@...el.com>
To:	David Miller <davem@...emloft.net>
Cc:	"mel@....ul.ie" <mel@....ul.ie>,
	"Chatre, Reinette" <reinette.chatre@...el.com>,
	"elendil@...net.nl" <elendil@...net.nl>,
	"Larry.Finger@...inger.net" <Larry.Finger@...inger.net>,
	"linville@...driver.com" <linville@...driver.com>,
	"penberg@...helsinki.fi" <penberg@...helsinki.fi>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"ipw3945-devel@...ts.sourceforge.net" 
	<ipw3945-devel@...ts.sourceforge.net>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"Krauss, Assaf" <assaf.krauss@...el.com>,
	"johannes@...solutions.net" <johannes@...solutions.net>,
	"Abbas, Mohamed" <mohamed.abbas@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: alloc skb based on a given data buffer

On Tue, 2009-09-15 at 16:33 +0800, David Miller wrote:
> From: Zhu Yi <yi.zhu@...el.com>
> Date: Tue, 15 Sep 2009 16:30:20 +0800
> 
> > This way, device drivers can allocate the Rx buffers with their own size
> > and alignment requirement. i.e. do an order-1 page allocation directly
> > with free_pages() in the iwlagn driver for a 256 bytes aligned 8K Rx
> > buffer. After DMA is finished, drivers can use the above function to
> > assemble an skb based on the Rx buffer. It should resolve the problem
> > for requiring an order-2 allocation by alloc_skb() in the first place.
> 
> You can create paged RX skbs just like drivers such as niu.c
> and others already do, there is no need for special APIs for
> this.

Thanks. So we can put the 8K buffer into 2 skb_shinfo()->frags[] slots
and set nr_frags to 2, right? Is this supported allover the network code
already? At a first glance, I didn't find any frags handling in mac80211
stack.

Thanks,
-yi

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