From: Daniel Borkmann <daniel@iogearbox.net>
Sent: Monday, August 31, 2020 1:33 PM
To: Ramamurthy, Harshitha <redacted>;
bpf@vger.kernel.org; netdev@vger.kernel.org; ast@kernel.org;
davem@davemloft.net; kuba@kernel.org
Cc: dsahern@gmail.com; Duyck, Alexander H
[off-list ref]; Herbert, Tom [off-list ref]
Subject: Re: [PATCH bpf-next] bpf: add bpf_get_xdp_hash helper function

On 8/31/20 9:25 PM, Harshitha Ramamurthy wrote:

quoted

This patch adds a helper function called bpf_get_xdp_hash to calculate
the hash for a packet at the XDP layer. In the helper function, we
call the kernel flow dissector in non-skb mode by passing the net
pointer to calculate the hash.

So this commit msg says 'what' the patch does, but says nothing about 'why'
it is needed especially given there's the 1 mio insn limit in place where it
should be easy to write that up in BPF anyway. The commit msg needs to
have a clear rationale which describes the motivation behind this helper..
why it cannot be done in BPF itself?

Okay, will add a rationale in the commit message in the next version for use-case. 

Thanks,
Harshitha

quoted

Changes since RFC:
- accounted for vlans(David Ahern)
- return the correct hash by not using skb_get_hash(David Ahern)
- call __skb_flow_dissect in non-skb mode