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Date: Tue, 1 Sep 2020 20:09:36 -0600 From: David Ahern <dsahern@...il.com> To: "Ramamurthy, Harshitha" <harshitha.ramamurthy@...el.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "ast@...nel.org" <ast@...nel.org>, "daniel@...earbox.net" <daniel@...earbox.net>, "davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org" <kuba@...nel.org> Cc: "Duyck, Alexander H" <alexander.h.duyck@...el.com>, "Herbert, Tom" <tom.herbert@...el.com> Subject: Re: [PATCH bpf-next] bpf: add bpf_get_xdp_hash helper function On 9/1/20 6:52 PM, Ramamurthy, Harshitha wrote: >> On 8/31/20 1:25 PM, Harshitha Ramamurthy wrote: >>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index >>> a613750d5515..bffe93b526e7 100644 >>> --- a/include/uapi/linux/bpf.h >>> +++ b/include/uapi/linux/bpf.h >>> @@ -3576,6 +3576,14 @@ union bpf_attr { >>> * the data in *dst*. This is a wrapper of copy_from_user(). >>> * Return >>> * 0 on success, or a negative error in case of failure. >>> + * >>> + * u32 bpf_get_xdp_hash(struct xdp_buff *xdp_md) >> >> I thought there was a change recently making the uapi reference xdp_md; >> xdp_buff is not exported as part of the uapi. > > Not sure what you mean - other xdp related helper functions still use xdp_buff as an argument. Could you point me to an example of what you are referring to? a patch from Jakub that is apparently not committed yet. >> >>> + memset(&keys, 0, sizeof(keys)); >>> + __skb_flow_dissect(dev_net(xdp->rxq->dev), NULL, >> &flow_keys_dissector, >>> + &keys, data, eth->h_proto, sizeof(*eth), len, >>> + FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL); >> >> By STOP_AT_FLOW_LABEL I take it you want this to be an L3 hash. Why not >> add a flags argument to the helper and let the hash be L3 or L4? > > I wrote this exactly how skb_get_hash calls skb_flow_dissect - with the same flag STOP_AT_FLOW_LABEL. So it should already cover L3 and L4 hash, right? From what I understand STOP_AT_FLOW_LABEL flag is used to only stop parsing when a flow label is seen in ipv6 packets. right; missed that. That means this new helper will always do an L4 hash for tcp/udp. Adding a flags argument now for the uapi allows a later change to make it an L3 hash.
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