netdev - Re: [PATCH net] bpf: expose netns inode to bpf programs

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Date:   Sat, 4 Feb 2017 19:22:03 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsa@...ulusnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Thomas Graf <tgraf@...g.ch>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net] bpf: expose netns inode to bpf programs

On Sat, Feb 4, 2017 at 7:18 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Sat, Feb 04, 2017 at 09:08:38AM -0800, Andy Lutomirski wrote:
>> > So use-case would be that someone wants to attach the very same
>> > prog via tc to various netdevs sitting in different netns, and
>> > that prog looks up a map, controlled by initns, with skb->netns_inum
>> > as key and the resulting value could contain allowed feature bits
>> > for that specific netns prog the skbs goes through? That would be
>> > a feature, not "concern", no? At the same time, it's up to the
>> > user or mgmt app what gets loaded so f.e. it might just as well
>> > tailor/optimize the progs individually for the devs sitting in
>> > netns-es to avoid such map lookup.
>>
>> Agreed.  I don't see why you would install the exact same program on
>> two sockets in different netnses if the program contains, say, an
>> ifindex.  Why not just install a variant with the right ifindex into
>> each socket?
>
> In other cases people prefer to have one program compiled once
> and thoroughly tested offline, since some folks are worried
> that on-the-fly compilation may cause generated code to
> be rejected by the verifier.

I would be rather surprised if someone wrote a program that did had an
expression like (ifindex == 17), tested it offline, and refused to
update the 17 based on the actual ifindex in use.

--Andy