Resending a previously submitted patch. I would really like to
see this patch go into 2.6.21.
Its a one-line patch to the spidernet device driver; it fixes
the operation of NFS for this device. This device is not
available on x86 platforms; accepting this patch will not
break x86. The device is integrated into the southbridge
for cell-based systems, and so is only available on those
systems. It is *not* used on the ps3, since the ps3 hides
this function under a hypervisor layer. Thus, the impact
ito the big wide world of applying this patch is small.
By contrast, the hurt to the small collection of affected
systems is high.
The rest of this email is a long description of the nature
of the bug.
--linas
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 <[EMAIL PROTECTED]>
Signed-off-by: Linas Vepstas <[EMAIL PROTECTED]>
----
diff --git a/drivers/net/spider_net.c b/drivers/net/spider_net.c
index 3b91af8..31507ac 100644
drivers/net/spider_net.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6.21-rc4-git4/drivers/net/spider_net.c
===================================================================
--- linux-2.6.21-rc4-git4.orig/drivers/net/spider_net.c 2007-03-19
12:51:21.000000000 -0500
+++ linux-2.6.21-rc4-git4/drivers/net/spider_net.c 2007-03-19
13:13:47.000000000 -0500
@@ -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_PARTIAL)
switch (skb->nh.iph->protocol) {
case IPPROTO_TCP:
hwdescr->dmac_cmd_status |= SPIDER_NET_DMAC_TCP;
-
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