netdev - Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in kernel

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Date:   Tue, 3 Apr 2018 19:09:09 -0600
From:   David Ahern <dsahern@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        "Md. Islam" <mislam4@...t.edu>, netdev@...r.kernel.org,
        David Miller <davem@...emloft.net>, stephen@...workplumber.org,
        agaceph@...il.com, Pavel Emelyanov <xemul@...nvz.org>,
        Eric Dumazet <edumazet@...gle.com>, brouer@...hat.com
Subject: Re: [PATCH v15 ] net/veth/XDP: Line-rate packet forwarding in kernel

On 4/3/18 11:37 AM, Alexei Starovoitov wrote:
> On Tue, Apr 03, 2018 at 11:14:00AM -0600, David Ahern wrote:
>> On 4/3/18 11:06 AM, Alexei Starovoitov wrote:
>>>> For 3 and 4 above I was referring to the route lookup part of it; sorry
>>>> for not being clear.
>>>>
>>>> For example, eth1 is enslaved to bond1 which is in VRF red. The lookup
>>>> needs to go to the table associated with the VRF. That is not known by
>>>> just looking at eth1. The code exists to walk the upper layers and do
>>>> the effective translations, just need to cover those cases.
>>>>
>>>> The VLAN part of it is a bit more difficult - ingress device for the
>>>> lookup should be eth1.100 for example not eth1, and then if eth1.100 is
>>>> enslaved to a VRF, ...
>>>>
>>>> None of it is that complex, just need to walk through the various use
>>>> cases and make sure bpf_ipv4_fwd_lookup and bpf_ipv6_fwd_lookup can do
>>>> the right thing for these common use cases.
>>> I'm a bit lost here. Why this is a concern?
>>> 'index' as argument that bpf prog is passing into the helper.
>>> The clsbpf program may choose to pass ifindex of the netdev
>>> it's attached to or some other one.
>>> In your patch you have:
>>> +BPF_CALL_3(bpf_ipv4_fwd_lookup, int, index, const struct iphdr *, iph,
>>> +	   struct ethhdr *, eth)
>>> +{
>>> +	struct flowi4 fl4 = {
>>> +		.daddr = iph->daddr,
>>> +		.saddr = iph->saddr,
>>> +		.flowi4_iif = index,
>>> +		.flowi4_tos = iph->tos & IPTOS_RT_MASK,
>>> +		.flowi4_scope = RT_SCOPE_UNIVERSE,
>>> +	};
>>>
>>> As you saying there is concern with .flowi4_iif = index line ?
>>
>> yes. BPF / XDP programs are installed on the bottom device ... e.g.,
>> eth1. The L3 lookup is not necessarily done on that device index.
> 
> right, but I still don't see any problem with this helper and vlans.
> If xdp program passes incorrect ifindex, it's program's mistake.
> If clsbpf attached to vlan passed good ifindex, the lookup will
> happen in the correct scope, but even in this case the prog
> can pass whatever ifindex it wants.
> 

I'll find some time update the bpf forwarding helpers and look at these
other cases in the next few weeks.