Re: Freeze with KVM_CLOCK, undocumented dependency VIRTIO_BLK -> VIRTIO_PCI

[Mark McLoughlin <markmc@redhat.com>]

On Sat, 2008-06-21 at 21:41 -0500, Anthony Liguori wrote:
> Bernhard Schmidt wrote:

> > b) apparently VIRTIO_BLK works only when VIRTIO_PCI and thus PCI is
> > enabled in the kernel. Otherwise the vda* device is not visible and the
> > guest does not find its root filesystem.
> >
> > Is this expected? If yes, is it possible to add the appropriate
> > dependency in the kernel configuration or amend the description
> > accordingly?
> >   
> 
> VIRTIO_BLK doesn't depend on VIRTIO_PCI.  VIRTIO_PCI allows you use to 
> virtio devices under KVM.
> 
> This is all documented FWIW in the Kconfig and in a number of places on 
> the wiki.

I wonder would it be useful to default to building in (i.e. not as a
module) virtio_pci if building with e.g. KVM_GUEST?

There's two issues here:

  1) It's easy to forget about virtio_pci - if we used KVM_GUEST as a 
     general "this kernel may be run on KVM" config, then it would be a 
     good hint that virtio_pci should be built

  2) Although we currently build virtio_pci as a module in Fedora, it 
     leads to a pretty strange situation where e.g. mkinitrd and 
     anaconda need to explicitly include the virtio_pci module; I 
     don't think there's analogous situation where bus probing logic is 
     in a module rather than built into the kernel

Cheers,
Mark.