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Date: Wed, 2 Oct 2013 18:27:30 +0200 From: Hannes Frederic Sowa <hannes@...essinduktion.org> To: jdmason@...zu.us Cc: Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org, kaber@...sh.net, herbert@...dor.apana.org.au, eric.dumazet@...il.com Subject: Neterion and UFO handling [was: Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need also be handled by UFO] Hi! I have a question regarding UFO and the neterion driver, which as the only one advertises hardware UFO support: The patch discusses in this thread http://thread.gmane.org/gmane.linux.network/284348/focus=285405 could change some semantics how packets are constructed before submitted to the driver. We currently guarantee that we have the MAC/IP/UDP header in skb->data and the payload is attached in the skb's frags. With the changes discussed in this thread it is possible that we also append to skb->data some amount of data which is not targeted for the header. From reading the driver sources it seems the hardware interprets the skb->data to skb_headlen as the header, so we could include some data in the fragments more than once. Do you think this change is safe? Otherwise I would suggest that the UFO capability is switched off until the driver signals the hardware the start and end of the headers correctly? I left the mail below intact which points to the specific place in s2io.c where I think the problem is. On Wed, Oct 02, 2013 at 08:14:27AM -0700, Eric Dumazet wrote: > On Wed, 2013-10-02 at 15:03 +0200, Hannes Frederic Sowa wrote: > > On Wed, Oct 02, 2013 at 02:12:07PM +0200, Hannes Frederic Sowa wrote: > > > Hi Eric! > > > > > > On Wed, Oct 02, 2013 at 03:41:28AM -0700, Eric Dumazet wrote: > > > > On Wed, 2013-10-02 at 10:58 +0200, Jiri Pirko wrote: > > > > > Wed, Oct 02, 2013 at 01:25:34AM CEST, hannes@...essinduktion.org wrote: > > > > > >- if (((length > mtu) || (skb && skb_is_gso(skb))) && > > > > > >+ if (((length > mtu) || (skb && skb_has_frags(skb))) && > > > > > > > > > > > > > > This seems correct to me. sk_is_gso would work as well is you apply my > > > > > patch "[patch net] ip6_output: do skb ufo init for peeked non ufo skb as > > > > > well" which does the setting of gso_size. > > > > > > > > Well, skb having frags or not should not be a concern : > > > > Thats an allocation choice (lets say to avoid high order allocations). > > > > > > > > Setting gso_size is probably better. > > > > > > e89e9cf539a28df7d0eb1d0a545368e9920b34ac ("[IPv4/IPv6]: UFO Scatter-gather > > > approach") states: > > > > > > " > > > skb->data will contain MAC/IP/UDP header and skb_shinfo(skb)->frags[] > > > contains the data payload. The skb->ip_summed will be set to CHECKSUM_HW > > > indicating that hardware has to do checksum calculation. Hardware should > > > compute the UDP checksum of complete datagram and also ip header checksum of > > > each fragmented IP packet. > > > " > > > > > > This is the reason why I tried not to update the gso_size. If it is ok, I am > > > fine with that. > > > > Especially, drivers/net/ethernet/neterion/s2io.c states that the first dma > > mapping (skb->data with skb_headlen, which is fine) is used as the inband > > header: > > > > if (offload_type == SKB_GSO_UDP) > > frg_cnt++; /* as Txd0 was used for inband header */ > > > > That is my only other hint that we maybe should not update gso_size and > > gso_type. I guess software fallback does not have this problem, but I won't > > have time to check until this evening. > > > > I am really not sure if just setting gso_size does not break neterion UFO > > offloading. :/ > > Well, just ask Jon Mason to double check ;) > > I think the commit intent was to set gso_size : > > skb_shinfo(skb)->ufo_size will indicate the length of data part in each IP > fragment going out of the adapter after IP fragmentation by hardware. > > The fact that it states "skb->data will contain MAC/IP/UDP header and > skb_shinfo(skb)->frags[] contains the data payload." seems irrelevant. > > If Neterion driver mandates that skb->head *only* contains the > MAC/IP/UDP header, that should be handled in the driver itself. Thanks Eric for clearing this up. I really thought it would be the common pattern for UFO to have only headers in skb->data, so I didn't bother to ask in the first place. Thanks, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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