netdev - Re: [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs in the egress path

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Date:   Sun, 2 Feb 2020 10:59:10 -0700
From:   David Ahern <dsahern@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
        prashantbhole.linux@...il.com, jasowang@...hat.com,
        davem@...emloft.net, jbrouer@...hat.com, mst@...hat.com,
        toshiaki.makita1@...il.com, daniel@...earbox.net,
        john.fastabend@...il.com, ast@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, andriin@...com,
        David Ahern <dahern@...italocean.com>
Subject: Re: [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs
 in the egress path

On 1/25/20 9:54 PM, Alexei Starovoitov wrote:
> On Sat, Jan 25, 2020 at 06:43:36PM -0700, David Ahern wrote:
>>
>> That said, Martin's comment throws a wrench in the goal: if the existing
>> code does not enforce expected_attach_type then that option can not be
>> used in which case I guess I have to go with a new program type
>> (BPF_PROG_TYPE_XDP_EGRESS) which takes a new context (xdp_egress_md),
>> has different return codes, etc.
> 
> This is acceptable risk. We did such thing in the past. The chances of
> user space breakage are extremely low.
> 

Ultimately that is a decision for the maintainers. Code wise both
iproute2 and libbpf always initialize bpf_attr to 0 and given the many
uses of that union it seems odd that someone would initialize one field
at a time.

Unless someone comes back with a strong 'hell, no' I am planning to send
the next RFC version with the current API.