netdev - Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs

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Date:   Mon, 25 May 2020 14:15:32 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     David Ahern <dsahern@...il.com>, David Ahern <dsahern@...nel.org>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, brouer@...hat.com,
        daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com, andriin@...com
Subject: Re: [PATCH RFC bpf-next 0/4] bpf: Add support for XDP programs in DEVMAPs

David Ahern <dsahern@...il.com> writes:

> On 5/22/20 9:59 AM, Toke Høiland-Jørgensen wrote:
>> David Ahern <dsahern@...nel.org> writes:
>> 
>>> Implementation of Daniel's proposal for allowing DEVMAP entries to be
>>> a device index, program id pair. Daniel suggested an fd to specify the
>>> program, but that seems odd to me that you insert the value as an fd, but
>>> read it back as an id since the fd can be closed.
>> 
>> While I can be sympathetic to the argument that it seems odd, every
>> other API uses FD for insert and returns ID, so why make it different
>> here? Also, the choice has privilege implications, since the CAP_BPF
>> series explicitly makes going from ID->FD a more privileged operation
>> than just querying the ID.
>> 
>
> I do not like the model where the kernel changes the value the user
> pushed down.

Yet it's what we do in every other interface where a user needs to
supply a program, including in prog array maps. So let's not create a
new inconsistent interface here...

-Toke