Re: [PATCH bpf-next v3 2/4] bpf: Improve error reporting for freplace attachment failure

[Leon Hwang <leon.hwang@linux.dev>]

On 18/2/25 11:01, Alexei Starovoitov wrote:
> On Mon, Feb 17, 2025 at 7:44 AM Leon Hwang <leon.hwang@linux.dev> wrote:
>>
>> When a freplace program fails to attach to a target, the error message
>> lacks details, making debugging difficult. This patch enhances error
>> reporting by providing a log that explains why the attachment failed.
> 
> Agree that it lacks details...
> 
>> For example, if a freplace program tries to attach to a static function,
>> the log now includes:
>>
>> libbpf: prog 'new_test_pkt_access': failed to attach to freplace: -EINVAL
>> libbpf: prog 'new_test_pkt_access': attach log: subprog_tail() is not a global function
> 
> ... but adding to uapi for a minor usability improvement...
> not a long term path that is worth taking.
> Especially since freplace is special. Users don't interact with it
> directly. The interaction is typically done through libraries.
> So this extra verbosity won't help users directly, but will
> help people who write libraries. Nice, but no.

What if libbpf allows users to interact with it directly?

As for cilium/ebpf library, it will be able to provide the error message
to users like:

create link: subprog_tail() is not a global function

instead of:

create link: invalid argument

Thanks,
Leon