Re: [PULL 07/20] virtio-net: Do not propagate ebpf-rss-fds errors

[Akihiko Odaki]

On 2024/06/05 19:23, Daniel P. Berrangé wrote:
> On Tue, Jun 04, 2024 at 03:37:42PM +0800, Jason Wang wrote:
> > From: Akihiko Odaki <akihiko.odaki@daynix.com>
> >
> > Propagating ebpf-rss-fds errors has several problems.
> >
> > First, it makes device realization fail and disables the fallback to the
> > conventional eBPF loading.
>
> AFAICT, this is not a bug - this is desired behaviour.
>
> If the user/mgmt app has told QEMU to use FDs it has passed
> in, then any failure to do this *MUST* be treated as a fatal
> error. Falling back to other codepaths is ignoring a direct
> user request.

The FD options are more like an assistance rather than a request. When 
QEMU does not have a permission to load eBPF programs, a user can get 
the eBPF programs with the request-ebpf command of QMP, load it, and 
pass the FDs to QEMU.

A user must not to use the option to pass eBPF programs not included in 
QEMU since we don't have a stable ABI. Nobody should want to do that 
anyway since the function of the eBPF program is restricted with the 
virtio spec.

Regards,
Akihiko Odaki