[Libvir] Fix handling of HVM boot parameters

[Jeremy Katz]

On Thu, 2006-08-10 at 05:08 -0400, Daniel Veillard wrote:
> On Wed, Aug 09, 2006 at 09:33:11PM -0400, Jeremy Katz wrote:
> > On Thu, 2006-08-10 at 01:00 +0100, Daniel P. Berrange wrote:
> > > I meant to include a complete example XML doc showing the changes in
> > > place, so here is a XML dump from a HVM domain which has been booted
> > > off a CDROM:
> > [snip]
> > >     <disk type='file'>
> > >       <source file='/root/foo.img'/>
> > >       <target dev='ioemu:hda'/>
> > >     </disk>
> > 
> > Given what we know is coming, does it make sense to drop the ioemu: here
> > and just have it be implied for HVM guests?  Accept it if it's there
> > (and then drop it if we're on xend 3.0.3), but not really show it?
> 
>   Sound sensible, the problem is detecting the version of xend, 
> of course you can ask xend, you will get the exact version of the
> compiler used to compile it, but when it comes to xen version itself
>   (xen_major 3) (xen_minor 0) (xen_extra -unstable)
> which makes things a bit hard to distinguish 3.0.2 from 3.0.3 :-\
> We could try to use the changest but it's not available in our build
> either.

Yeah, unfortunately, this is just going to be a general problem :(

> > Then again, not 100% sure how all of this is going to interact when we
> > start having PV drivers for HVM guests :-/
> > 
> > >     <disk type='file'>
> > >       <source file='/root/boot.iso'/>
> > >       <target dev='cdrom'/>
> > >     </disk>
> > 
> > Similarly, instead of target dev='cdrom', does it make more sense to
> > have a devicetype (or something) that's an attribute of the disk rather
> > than a magic device?
> 
>   There is the read-only attribute. For example UML has no specific way
> to indicate an emulated CD-ROM, there is just a read-only command line 
> flag.
> 
>      <disk type='file'>
>        <source file='/root/boot.iso'/>
>        <target dev='hdc'/>
>        <readonly/>
>      </disk>
> 
>   After all since we don't have hardware to tell us what kind of device
> it is, it is really a matter of what kind of accesses are allowed. How
> it is mapped underneath depends on the engine used, but should probably
> not affect the XML format.

But read-only isn't all that you want -- think about giving access to a
CD-R drive.  It's not read-only, but we still need to have it exposed as
a CD device.  And with things like the bios for qemu and HVM guests, if
a device is a CD-ROM or a hard drive makes a large difference.

Thinking out loud, what if we went with something like
  <cdrom type='file'>
    <source file='/root/boot.iso'/>
    <target dev='hdc'/>
  </cdrom>
for CDs and then similarly <floppy .../> for floppies

Jeremy