Re: [PATCH RFC] virtio-pci: new config layout: using memory BAR

[Paolo Bonzini <pbonzini@redhat.com>]

Il 28/05/2013 19:32, Michael S. Tsirkin ha scritto:
>>> > > +
>>> > > +    switch (addr) {
>>> > > +    case offsetof(struct virtio_pci_common_cfg, device_feature_select):
>>> > > +        return proxy->device_feature_select;
>> > 
>> > Oh dear no...  Please use defines like the rest of QEMU.
> Any good reason not to use offsetof?

I'm not sure it's portable to use it in case labels.  IIRC, the
definition ((int)&(((T *)0)->field)) is not a valid C integer constant
expression.  Laszlo?

> I see about 138 examples in qemu.

Almost all of them are about fields in the host, not the guest, and none
of them are in case statements.

Paolo

> 
> Anyway, that's the way Rusty wrote it in the kernel header -
> I started with defines.
> If you convince Rusty to switch I can switch too,
> but I prefer reusing same structures as linux even if
> for now I've given up on reusing same headers.
> 
>