On 1/17/23 3:46 PM, Paul Moore wrote: >> >> In the BIG TCP case, when is the IPv4 header zero'd out? Currently >> cipso_v4_skbuff_setattr() is called in the NF_INET_LOCAL_OUT and >> NF_INET_FORWARD chains, is there an easy way to distinguish between a >> traditional segmentation offload mechanism, e.g. GSO, and BIG TCP? If >> BIG TCP allows for arbitrarily large packets we can just grow the >> skb->len value as needed and leave the total length field in the IPv4 >> header untouched/zero, but we would need to be able to distinguish >> between a segmentation offload and BIG TCP. > > Keeping the above questions as they still apply, rather I could still > use some help understanding what a BIG TCP packet would look like > during LOCAL_OUT and FORWARD. skb->len > 64kb. you don't typically look at the IP / IPv6 header and its total length field and I thought the first patch in the series added a handler for doing that. > >>>> In the GRO case, is it safe to grow the packet such that skb->len is >>>> greater than 64k? I presume that the device/driver is going to split >>>> the packet anyway and populate the IPv4 total length fields in the >>>> header anyway, right? If we can't grow the packet beyond 64k, is >>>> there some way to signal to the driver/device at runtime that the >>>> largest packet we can process is 64k minus 40 bytes (for the IPv4 >>>> options)? >>> >>> at runtime, not as far as I know. >>> It's a field of the network device that can be modified by: >>> # ip link set dev eth0 gro_max_size $MAX_SIZE gso_max_size $MAX_SIZE >> >> I need to look at the OVS case above, but one possibility would be to >> have the kernel adjust the GSO size down by 40 bytes when >> CONFIG_NETLABEL is enabled, but that isn't a great option, and not >> something I consider a first (or second) choice. > > Looking more at the GSO related code, this isn't likely to work. > icsk_ext_hdr_len is adjusted by cipso for its options. Does that not cover what is needed?
