netdev - Re: netfront for review

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Date:	Thu, 03 May 2007 16:34:28 +0200
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Keir Fraser <Keir.Fraser@...cam.ac.uk>
Subject: Re: netfront for review

Jeremy Fitzhardinge wrote:
> Gerd Hoffmann wrote:
>>> Gerd, in change 11196:b85da7cd9ea5 "front: Fix rx buffer leak when
>>> tearing down an interface." you added a call to
>>> "add_id_to_freelist(np->rx_skbs, id);".  However, rx_skbs doesn't have
>>> an extra entry for the list head, and there's never any corresponding
>>> get_id_from_freelist(np->rx_skbs).  What should it be?
>> The function has an effect in page flipping mode only.  It walks the
>> whole list of rx skbufs (id is the loop variable ...), checks whenever
>> they are handed out to the frontend driver to fill in packet data and
>> not returned yet, and if so reclaim them ...
> 
> Yes, but why use add_id_to_freelist?  rx_skbs are not being used on a
> freelist anywhere else.  It just means the rx_skb array gets filled with
> small integers, but the rest of the code assumes they're either NULL or
> an skb pointer.

Hmm, good point.  Have to look at the code again, it has been some time 
I've written that, and it took me some time to figure how all the grant 
table stuff works ...

Maybe the add_id_to_freelist() call can simply be dropped.  The whole 
interface is released shortly thereafter, probably thats why filling the 
freelist with yunk never caused any problems ...

cheers,
   Gerd

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