On Mon, Dec 20, 2021 at 07:18:42PM -0800, Yonghong Song wrote:

quoted

On 12/20/21 12:40 PM, Tyler Wear wrote:

quoted

New bpf helper function BPF_FUNC_skb_change_dsfield "int 
bpf_skb_change_dsfield(struct sk_buff *skb, u8 mask, u8 value)".
BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog which currently can be 
attached to the ingress and egress path. The helper is needed 
because this type of bpf_prog cannot modify the skb directly.

Used by a bpf_prog to specify DS field values on egress or ingress.

Maybe you can expand a little bit here for your use case?
I know DS field might help but a description of your actual use case 
will make adding this helper more compelling.

+1.  More details on the use case is needed.
Also, having an individual helper for each particular header field is too specific.

For egress, there is bpf_setsockopt() for IP_TOS and IPV6_TCLASS and it can be called in other cgroup hooks. e.g.
BPF_PROG_TYPE_SOCK_OPS during tcp ESTABLISHED event.
There is an example in tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c.
Is it enough for egress?

Using bpf_setsockopt() has 2 issues: 1) it changes the userspace visible state 2) won't work with udp sendmsg cmsg