[PATCH] spidernet: Fix problem sending IP fragments

[Chris Engel]

I tried to apply this patch to 2.6.21-rc2 and CHECKSUM_HW appears to be
changed to CHECKSUM_COMPLETE at least in what I could find in skbuff.h .

Is CHECKSUM_COMPLETE the right value to use instead of CHECKSUM_HW ?

On 2/28/07, Norbert Eicker <n.eicker at fz-juelich.de> wrote:
>
> Hi,
>
> I found out that the spidernet-driver is unable to send fragmented IP
> frames.
>
> Let me just recall the basic structure of "normal" UDP/IP/Ethernet
> frames (that actually work):
> - It starts with the Ethernet header (dest MAC, src MAC, etc.)
> - The next part is occupied by the IP header (version info, length of
> packet, id=0, fragment offset=0, checksum, from / to address, etc.)
> - Then comes the UDP header (src / dest port, length, checksum)
> - Actual payload
> - Ethernet checksum
>
> Now what's different for IP fragment:
> - The IP header has id set to some value (same for all fragments),
> offset is set appropriately (i.e. 0 for first fragment, following
> according to size of other fragments), size is the length of the frame.
> - UDP header is unchanged. I.e. length is according to full UDP
> datagram, not just the part within the actual frame! But this is only
> true within the first frame: all following frames don't have a valid
> UDP-header at all.
>
> The spidernet silicon seems to be quite intelligent: It's able to
> compute (IP / UDP / Ethernet) checksums on the fly and tests if frames
> are conforming to RFC -- at least conforming to RFC on complete frames.
>
> But IP fragments are different as explained above:
> I.e. for IP fragments containing part of a UDP datagram it sees
> incompatible length in the headers for IP and UDP in the first frame
> and, thus, skips this frame. But the content *is* correct for IP
> fragments. For all following frames it finds (most probably) no valid
> UDP header at all. But this *is* also correct for IP fragments.
>
> The Linux IP-stack seems to be clever in this point. It expects the
> spidernet to calculate the checksum (since the module claims to be able
> to do so) and marks the skb's for "normal" frames accordingly
> (ip_summed set to CHECKSUM_HW).
> But for the IP fragments it does not expect the driver to be capable to
> handle the frames appropriately. Thus all checksums are allready
> computed. This is also flaged within the skb (ip_summed set to
> CHECKSUM_NONE).
>
> Unfortunately the spidernet driver ignores that hints. It tries to send
> the IP fragments of UDP datagrams as normal UDP/IP frames. Since they
> have different structure the silicon detects them the be not
> "well-formed" and skips them.
>
> The following one-liner against 2.6.21-rc2 changes this behavior. If the
> IP-stack claims to have done the checksumming, the driver should not
> try to checksum (and analyze) the frame but send it as is.
>
> Signed-off-by: Norbert Eicker <n.eicker at fz-juelich.de>
> ---
> diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c
> index 3b91af8..31507ac 100644
> --- a/drivers/net/spider_net.c
> +++ b/drivers/net/spider_net.c
> @@ -719,7 +719,7 @@ spider_net_prepare_tx_descr(struct spide
>                         SPIDER_NET_DESCR_CARDOWNED |
> SPIDER_NET_DMAC_NOCS;
>         spin_unlock_irqrestore(&chain->lock, flags);
>
> -       if (skb->protocol == htons(ETH_P_IP))
> +       if (skb->protocol == htons(ETH_P_IP) && skb->ip_summed ==
> CHECKSUM_HW)
>                 switch (skb->nh.iph->protocol) {
>                 case IPPROTO_TCP:
>                         hwdescr->dmac_cmd_status |= SPIDER_NET_DMAC_TCP;
>
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>



-- 
   Chris
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