From: Alexei Starovoitov <ast@plumgrid•com>
To: Tom Herbert <tom@herbertland•com>,
Daniel Borkmann <daniel@iogearbox•net>
Cc: "David S. Miller" <davem@davemloft•net>,
Linux Kernel Network Developers <netdev@vger•kernel.org>
Subject: Re: [PATCH net-next] ebpf: add skb->hash to offset map for usage in {cls,act}_bpf or filters
Date: Sun, 2 Aug 2015 23:16:12 -0700 [thread overview]
Message-ID: <55BF072C.3000302@plumgrid.com> (raw)
In-Reply-To: <CALx6S35Xw-14Z8=w2cg7dFFzfkEmkjuqU=37uG3Tb-OoW2JEoA@mail.gmail.com>
On 8/2/15 6:09 PM, Tom Herbert wrote:
>> I was thinking whether to add skb_get_hash(), but then concluded the
>> >raw skb->hash seems fine in this case: we can directly access the hash
>> >w/o extra eBPF helper function call, it's filled out by many NICs on
>> >ingress, and in case the entropy level would not be sufficient, people
>> >can still implement their own specific sw fallback hash mix anyway.
>> >
> Maybe we should add the skb_get_hash also? It doesn't as useful if
> some scenarios we get a valid hash and in others not.
we also discussed whether it makes sense to expose l4_hash and sw_hash
bits as well. imo, seems a bit of overkill, since such call into sw hash
function like this exposes the logic of flow_dissector looking into
inner header. There are pros and cons. I think if we expose
flow_dissector it's cleaner to do it directly (instead of skb_get_hash).
Alternatively we can obfuscate skb_get_hash by calling it
'please compute some a hash on a packet somehow', but that will be
awkward to use. The programs can compute whatever hash they like anyway.
next prev parent reply other threads:[~2015-08-03 6:16 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-31 22:46 [PATCH net-next] ebpf: add skb->hash to offset map for usage in {cls,act}_bpf or filters Daniel Borkmann
2015-08-03 0:21 ` David Miller
2015-08-03 1:09 ` Tom Herbert
2015-08-03 6:16 ` Alexei Starovoitov [this message]
2015-08-03 12:49 ` Daniel Borkmann
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