Re: ebpf functions can fail without setting an error

[Markus Armbruster <armbru@redhat.com>]

Markus Armbruster <armbru@redhat.com> writes:

> Daniel P. Berrangé <berrange@redhat.com> writes:
>
>> On Thu, Aug 07, 2025 at 03:14:56PM +0200, Markus Armbruster wrote:
>>> Three functions in ebpf_rss.h take an Error ** argument and return bool.
>>> Good.
>>> 
>>> They can all fail without setting an error.  Not good.
>>> 
>>> The failures without error are:
>>> 
>>> * All three stubs in ebpf_rss-stub.c always.  Oversight?
>>
>> Opps, yes, we really should have added error_setg() calls for diagnosis
>> if someone tries to use eBPF when QEMU build has it disabled.

Easy enough, but...

> Some stubs exist only to mollify the linker.  They are not meant to be
> called.  They should abort(), optionally with lipstick.
>
> Other stubs are called and should fail nicely.
>
> Can you tell me offhand which kind these are?

If calling these stubs is possible, I'd like to know how I can get them
called, so I can test the errors I add.

If calling is not possible, I'd rather add abort()s.

I tried to figure out whether calling is possible, but it ended in
confusion.  Can you help?

>>> * Non-stub ebpf_rss_load() when ebpf_rss_is_loaded().  Are these
>>>   reachable?
>>
>> This scenario should never happen, and we should add a call like
>>
>>   error_setg(errp, "eBPF program is already loaded");
>>
>> to report it correctly.
>
> Is it a programming error when it happens?

This question is still open as well.