Re: ebpf functions can fail without setting an error

[Markus Armbruster <armbru@redhat.com>]

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.

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?

>> * 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?