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Description of problem:
Control 'disable-modern' and 'disable-legacy' flags for all virtio devices
Required in order to avoid compatibility issues.
Version-Release number of selected component (if applicable):
How reproducible:
Steps to Reproduce:
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Actual results:
Expected results:
Additional info:
(In reply to Amnon Ilan from comment #0)
> Description of problem:
>
> Control 'disable-modern' and 'disable-legacy' flags for all virtio devices
> Required in order to avoid compatibility issues.
What compatibility issues ? IIUC, QEMU ought to negotiate the right settings for virtio with the guest OS. Adding these flags to libvirt XML for guests seems like quite a unpleasant thing to do.
In 7.3 the default Virtio mode will be "transitional": both legacy and modern are enabled. Since "modern" (Virtio 1) is new, there may be some issues that will not
be discovered by QE. In such a case we can run into problems if we have no way
to force the driver to "legacy" mode. That is why 'disable-modern' is important.
Now for the imprtance of 'disable-legacy' (less important, but yet): when we wish to boot from a virtio device and the device is in legacy mode, the device will require io space, and this space is very limited (as an example, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1175124 ).
In such cases we would like to do 'disable-legacy' since Virtio 1 does not require the io space.
Both cases are related to customer usage and not only testing (where qemu command-line could do the job).