> -----Original Message----- > From: David Miller [mailto:davem@xxxxxxxxxxxxx] > Sent: Wednesday, April 9, 2014 10:01 AM > To: KY Srinivasan > Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; > jasowang@xxxxxxxxxx > Subject: Re: [PATCH net 3/3] Drivers: net: hyperv: Address UDP checksum > issues > > From: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> > Date: Tue, 8 Apr 2014 12:46:11 -0700 > > > } else if (net_trans_info & INFO_UDP) { > > - csum_info->transmit.udp_checksum = 1; > > + /* UDP checksum offload is not supported on ws2008r2. > > + * Furthermore, on ws2012 and ws2012r2, there are some > > + * issues with udp checksum offload from Linux guests. > > + * (these are host issues). > > + * For now compute the checksum here. > > + */ > > + struct udphdr *uh = udp_hdr(skb); > > + u16 udp_len = ntohs(uh->len); > > + > > + uh->check = 0; > > + uh->check = csum_tcpudp_magic(ip_hdr(skb)->saddr, > > + ip_hdr(skb)->daddr, > > + udp_len, IPPROTO_UDP, > > + csum_partial(uh, udp_len, 0)); > > + if (uh->check == 0) > > + uh->check = CSUM_MANGLED_0; > > + > > + csum_info->transmit.udp_checksum = 0; > > You absolutely cannot mangle packet header contents without first COW'ing > the SKB to make sure it's writable. > > Otherwise network taps like tcpdump, and any other entity with a reference > to the packet, can see inconsistent state. Thanks Dave. I will COW the SKB before changing the checksum value. I do have a question though. I looked at a bunch of hardware drivers and they modify the header information, specially checksum field and I could not see where they had COWed the skb. I was grepping for skb_cow in these drivers. Regards, K. Y _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
