netdev - Re: [RFC] allow skb->head to point/alias to first skb frag

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Message-Id: <20120426.051800.637617874638567499.davem@davemloft.net>
Date:	Thu, 26 Apr 2012 05:18:00 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ilpo.jarvinen@...sinki.fi, rick.jones2@...com,
	netdev@...r.kernel.org, therbert@...gle.com, ncardwell@...gle.com,
	maze@...gle.com, ycheng@...gle.com
Subject: Re: [RFC] allow skb->head to point/alias to first skb frag

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 26 Apr 2012 11:10:02 +0200

> The 'frag' would have a known size : 2048 bytes
> 
> But the end of it would be used by struct skb_shared_info
> 
> so data_len would be 0 in fact.
> 
> This would look like a regular linear skb.
> 
> Just a bit set in skb to say : Warning, skb->head was not kmalloced :
> replace kfree(head) by put_page(...)
> 
> And this bit would be tested in GRO or tcp merge to 'upgrade' this
> skb->head to proper page/frag

And what happens if this ends up in a piece of code which wants to
append a page frag?

Or a piece of code which copies an SKB, including page frag parts?

All I'm saying is that the number of tests necessary to make this work
properly might become prohibitive.
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