netdev - Re: [PATCH net-next] libbpf: add function to setup XDP

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Date:   Sun, 10 Dec 2017 14:07:12 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Leblond <eric@...it.org>, Jakub Kicinski <kubakici@...pl>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org, daniel@...earbox.net
Subject: Re: [PATCH net-next] libbpf: add function to setup XDP

On 12/10/17 1:34 PM, Eric Leblond wrote:
>> Would it be possible to print out or preferably return to the caller
>> the ext ack error message?  A couple of drivers are using it for XDP
>> mis-configuration reporting instead of printks.  We should encourage
>> other to do the same and support it in all user space since ext ack 
>> msgs lead to much better user experience.
> 
> I've seen the kind of messages displayed by reading at kernel log. They
> are really useful and it looks almost mandatory to be able to display
> them.
> 
> Kernel code seems to not have a parser for the ext ack error message.
> Did I miss something here ?
>  
> Looking at tc code, it seems it is using libmnl to parse them and I
> doubt it is a good idea to use that in libbpf as it is introducing a
> dependency.
> 
> Does someone has an existing parsing code or should I write on my own ?

I had worked on extack for libbpf but seem to have lost the changes.

Look at the commits here:
    https://github.com/dsahern/iproute2/commits/ext-ack

I suggest using this:

https://github.com/dsahern/iproute2/commit/b61e4c7dd54a5d3ff98640da4b480441cee497b2

to bring in nlattr from lib/nlattr (as I recall lib/nlattr can not be
used directly). From there, use this one:

https://github.com/dsahern/iproute2/commit/261f7251e6704d565b91e310faabbbb7e18d14a1

to see what is needed for extack support.

Really not that much code to add.