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

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Date:   Tue, 12 Dec 2017 03:23:04 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     David Ahern <dsahern@...il.com>, Eric Leblond <eric@...it.org>,
        Jakub Kicinski <kubakici@...pl>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org
Subject: Re: [PATCH net-next] libbpf: add function to setup XDP

On 12/10/2017 10:07 PM, David Ahern wrote:
> 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.

+1, ext ack support would improve troubleshooting a lot here; please
add and respin. Thanks, Eric!