Hi Chris,
I think you have a point. As an alternative I can allocate some
extra buffer space for buffer 2 (Ethernet payload) to begin with and in Rx
path copy the buffer 1(Ethernet header) to the start of buffer 2(skb_push).
This can then be passed to the upper layer (after eth_type_trans call).
I did try fragmented SKB on Rx but it didn't seem to work. If any one can
give me some pointers on how to get this working, I would implement 2Buff
mode using this method and avoid a copy in fast path.
Koushik
> -----Original Message-----
> From: Chris Leech [mailto:chris.leech@xxxxxxxxx]
> Sent: Thursday, October 14, 2004 1:49 PM
> To: Raghavendra Koushik
> Cc: Jeff Garzik; ravinandan.arakali@xxxxxxxx; Francois Romieu;
> netdev@xxxxxxxxxxx; leonid.grossman@xxxxxxxx; rapuru.sriram@xxxxxxxx
> Subject: Re: [PATCH 2.6.9-rc2 8/8] S2io: two buffer mode
>
> On Thu, 14 Oct 2004 11:33:13 -0700, Raghavendra Koushik
> <raghavendra.koushik@xxxxxxxx> wrote:
>
> > > 1) can this not be done with SKB fragments?
> > >
> > To acheve what is required, the H/W still has to split the Rx'ed frame
> into
> > 2 parts. By implementing this through the SKB fragments method, the only
> > thing we avoid is usage of ba_0 and ba_1 fields, but note that none of
> these
> > are allocated or freed in fast path. They are all pre-allocated buffers
> > (along with the Rx descriptors) and hence won't hit the Rx side
> performance.
> > Also by pulling down the eth_type_trans implementation partially into
> the
> > driver any kind of copy during Rx is also avoided.
>
> This change would pass skbs from the driver without the MAC header?
> What happens in a bridging configuration? And dev->hard_header_parse
> is set to eth_header_parse, which expects skb->mac.ethernet to be
> valid, so I think any use of packet sockets will result in a NULL
> dereference.
>
> - Chris
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