On Tue, Sep 04, 2007 at 08:48:43PM +0300, Michael S. Tsirkin wrote: > > Aren't you already summing all UD packets (inclusing multicast) in the > > driver before sending? Though, to be honest, I don't see this in your > > patch, so maybe not.. > > no
Yuk. Sending invalid UD packets is horrible. So it truely is all or nothing. Every gateway, embedded IP device, etc must support this or you cannot use it.. > > > > What if the RXing Linux IB side is acting as a forwarder to ethernet? > > > > It will forward corrupt packets if this option is set, right? > > > > > > No. The checksum will be calculated by the gateway before being sent on > > > the > > > ethernet interface. > > > > I thought linux only recomputed the checksum on the forwarding path if > > the skb was marked as needing checksum. Since you set the skb as > > already summed, there should be cases where invalid packets will be > > forwarded.. > > I don't set CHECKSUM_UNECESSARY, so linux will have to recompute the checksum. Eh? You set IPOIB_HEADER_F_HWCSUM on the TX path if the csum is invalid and the test that on the rx path to set CHECKSUM_UNNECESSARY. So, all badly csumed packets have CHECKSUM_UNECESSARY set. > > I'd be surprised if a real, hardware, IPoIB to XX device recomputed > > the checksum unconditionally. The typical approach is to do an > > incremental update of the checksum if you are changing the packet > > headers. This preserves the end-to-end-ness and also does not require > > buffering the entire packet before updating it. I was talking about real, existing HW gateways here, not Linux. I don't know of any reason a gateway would even touch the payload and require a L4 checksum update, let alone doing it non-incrementally.. > Since skb is not marked with CHECKSUM_COMPLETE, linux will > recompute the checksum IMO. MM, no, I don't think so. This checksum stuff is all about the L4 TCP/UDP checksum. If on RX the checksum is invalid the packet is dumped and it never gets into the forwarding code (ip_forward routine). Up until very recently ip_fowrard just unconditionally set ip_summed to CHECKSUM_NONE to reflect this. Of course CHECKSUM_NONE disables all checksum updates on the driver TX path. FWIW, CHECKSUM_COMPLETE is listed as an rx path option, no in tree driver tests it on the TX path. You should probably be using ip_summed != CHECKSUM_PARTIAL as a test in hard_header. With the new changes to ip_forward, maybe you could get away with setting CHECKSUM_PARTIAL in your RX path to get the TX of the final output device to regenerate the L4 checksum? Even so, sending out malformed UD packets strikes me as a compatability killer.. This would be much better as a RC only negotiated at CM feature. Jason _______________________________________________ general mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
