Messages in this thread | | | Date | Mon, 16 Jul 2018 15:30:04 -0700 | From | Alexei Starovoitov <> | Subject | Re: [PATCH] bpf: allow BPF programs access skb_shared_info->gso_segs field |
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On Sun, Jul 15, 2018 at 01:45:24AM -0700, Eddie Hao wrote: > This adds the ability to read gso_segs from a BPF program. This is useful > for user space monitoring systems to get gso_segs statistics for each > arbitrary group of flows defined by the BPF program. > > Signed-off-by: Eddie Hao <eddieh@google.com> > --- > include/uapi/linux/bpf.h | 1 + > net/core/filter.c | 9 +++++++++ > 2 files changed, 10 insertions(+) > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > index b7db3261c62d..282085445616 100644 > --- a/include/uapi/linux/bpf.h > +++ b/include/uapi/linux/bpf.h > @@ -2266,6 +2266,7 @@ struct __sk_buff { > /* ... here. */ > > __u32 data_meta; > + unsigned short gso_segs;
'short' will make it harder to extend due to struct hole. please use __u32 instead.
> }; > > struct bpf_tunnel_key { > diff --git a/net/core/filter.c b/net/core/filter.c > index b9ec916f4e3a..f17e249f3fbb 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -5820,6 +5820,15 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type, > bpf_target_off(struct sock_common, > skc_num, 2, target_size)); > break; > + > + case offsetof(struct __sk_buff, gso_segs): > + BUILD_BUG_ON(FIELD_SIZEOF(struct skb_shared_info, gso_segs) != > + sizeof(unsigned short)); > + off = offsetof(struct sk_buff, end); > + off += offsetof(struct skb_shared_info, gso_segs);
did you test this patch? Above math doesn't look correct. NET_SKBUFF_DATA_USES_OFFSET is not handled. At least one more LDX is needed.
> + *insn++ = BPF_LDX_MEM(BPF_SIZEOF(unsigned short), si->dst_reg, > + si->src_reg, off);
I think BUILD_BUG_ON is a bit of overkill when BPF_LDX_MEM can use BPF_FIELD_SIZEOF(struct skb_shared_info, gso_segs) instead.
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