On Sat, Feb 23, 2019 at 02:14:26AM +0100, Daniel Borkmann wrote:
> On 02/23/2019 02:06 AM, brakmo wrote:
> > This patch adds a new bpf helper BPF_FUNC_skb_ecn_set_ce
> > "int bpf_skb_ecn_set_ce(struct sk_buff *skb)". It is added to
> > BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog which currently can
> > be attached to the ingress and egress path. The helper is needed
> > because his type of bpf_prog cannot modify the skb directly.
> >
> > This helper is used to set the ECN field of ECN capable IP packets to ce
> > (congestion encountered) in the IPv6 or IPv4 header of the skb. It can be
> > used by a bpf_prog to manage egress or ingress network bandwdith limit
> > per cgroupv2 by inducing an ECN response in the TCP sender.
> > This works best when using DCTCP.
> >
> > Signed-off-by: Lawrence Brakmo <bra...@fb.com>
> > ---
> > include/uapi/linux/bpf.h | 10 +++++++++-
> > net/core/filter.c | 14 ++++++++++++++
> > 2 files changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 95b5058fa945..fc646f3eaf9b 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -2365,6 +2365,13 @@ union bpf_attr {
> > * Make a tcp_sock enter CWR state.
> > * Return
> > * 0 on success, or a negative error in case of failure.
> > + *
> > + * int bpf_skb_ecn_set_ce(struct sk_buf *skb)
> > + * Description
> > + * Sets ECN of IP header to ce (congestion encountered) if
> > + * current value is ect (ECN capable). Works with IPv6 and IPv4.
> > + * Return
> > + * 1 if set, 0 if not set.
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -2464,7 +2471,8 @@ union bpf_attr {
> > FN(spin_unlock), \
> > FN(sk_fullsock), \
> > FN(tcp_sock), \
> > - FN(tcp_enter_cwr),
> > + FN(tcp_enter_cwr), \
> > + FN(skb_ecn_set_ce),
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which
> > helper
> > * function eBPF program intends to call
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index ca57ef25279c..955369c6ed30 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -5444,6 +5444,18 @@ static const struct bpf_func_proto
> > bpf_tcp_enter_cwr_proto = {
> > .ret_type = RET_INTEGER,
> > .arg1_type = ARG_PTR_TO_TCP_SOCK,
> > };
> > +
> > +BPF_CALL_1(bpf_skb_ecn_set_ce, struct sk_buff *, skb)
> > +{
> > + return INET_ECN_set_ce(skb);
>
> Hm, but as mentioned last time, don't we have to ensure here that skb
> is writable (aka skb->data private to us before writing into it)?
INET_ECN_set_ce(skb) is also called from a few net/sched/sch_*.c
but I don't see how they ensure if a skb is writable.
May be I have missed something there that can also be borrowed and
reused here?
Thanks,
Martin
>
> > +}
> > +
> > +static const struct bpf_func_proto bpf_skb_ecn_set_ce_proto = {
> > + .func = bpf_skb_ecn_set_ce,
> > + .gpl_only = false,
> > + .ret_type = RET_INTEGER,
> > + .arg1_type = ARG_PTR_TO_CTX,
> > +};
> > #endif /* CONFIG_INET */
> >
> > bool bpf_helper_changes_pkt_data(void *func)
> > @@ -5610,6 +5622,8 @@ cg_skb_func_proto(enum bpf_func_id func_id, struct
> > bpf_prog *prog)
> > } else {
> > return NULL;
> > }
> > + case BPF_FUNC_skb_ecn_set_ce:
> > + return &bpf_skb_ecn_set_ce_proto;
> > #endif
> > default:
> > return sk_filter_func_proto(func_id, prog);
> >
>
> Thanks,
> Daniel
