[Xen-devel] Wondering about pv devcie configuration and usage

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

I know this is more of a design problem and maybe there are already changes to
solve that...

When looking at xen 4.1.1 and 3.0 kernels it looks to me that the decision about
unplugging is done based on what drivers are available, while the decision about
whether the blkfront driver makes the disk available is done based on the
theoretical major.

So when having a disk defined as "hda" in the config, a kernel that has the pci
frontend and the blk frontend available will first unplug the ide disk and then
refuse to use the pv disk because the hda major would not be the right one. Even
naming the disk xvda in the config will cause an emulated device to appear (if
unplugging is prevented).

I know this all goes back quite a while. Just wondering whether it would be an
acceptable approach to

- For a PV guest that defines sd? or hd? names, print a big warning and maybe
  map even before configuring the domain.
- For HVM guests, anything configured as hd? only gives emulated drives and
  anything declared as xvd? only gives pv disks.

It may be over simplified thinking...

-Stefan

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