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Re: [libvirt] [PATCH 03/18] qemu: Support disk model=virtio-{non-}transitional



On 01/18/2019 07:33 AM, Andrea Bolognani wrote:
> On Thu, 2019-01-17 at 12:52 -0500, Cole Robinson wrote:
>> +    if (has_tmodel) {
>> +        if (virQEMUCapsGet(qemuCaps, tmodel_cap))
>> +            virBufferAddLit(buf, "-transitional");
>> +
>> +        /* No error for if -transitional is not supported: our address
>> +         * allocation will force the device into plain PCI bus, which
>> +         * is functionally identical to standard 'virtio-XXX' behavior
>> +         */
>> +    } else if (has_ntmodel) {
>> +        if (virQEMUCapsGet(qemuCaps, ntmodel_cap)) {
>> +            virBufferAddLit(buf, "-non-transitional");
>> +        } else if (virQEMUCapsGet(qemuCaps,
>> +                                  QEMU_CAPS_VIRTIO_PCI_DISABLE_LEGACY)) {
>> +            virBufferAddLit(buf, ",disable-legacy=on");
>> +        } else {
>> +            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>> +                           _("virtio non-transitional model not supported "
>> +                             "for this qemu"));
>> +            return -1;
>> +        }
>> +    }
> 
> Would it make sense to be more explicit here? Current versions of
> QEMU default to disable-modern=off,disable-legacy=off for virtio-pci
> devices plugged into conventional PCI slots, but unless I'm mistaken
> that was not always the case, so it would perhaps be preferrable to
> not rely on that behavior and always explicitly set both disable-*
> options when the new devices are not available; if the options
> themselves are not available, then we should error out.
> 

I don't know enough to say, CCing ehabkost and danpb for more eyes

- Cole


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