[libvirt] [RFC] Explicit boot device ordering

[Jiri Denemark]

> > So for the first case, we could have something like
> > <os>
> >     <boot target='net1'/>
> >     <boot target='net0'/>
> >     <boot target='hdc'/>
> >     <boot target='hdb'/>
> > <os>
> > 
> > Where target attributes would match /domain/devices/*/target at dev
> 
> I'm not a huge fan of using */target at dev as the identifier for the
> device though, since that isn't an attribute that exists for all
> device types in the XML - only NICs + disks. This would make it
> hard to boot from a PCI NIC that has been passed through from the
> host using <hostdev>. It would be nice to use the unique device
> alises, but we only assign those at guest startup, and not letting
> the end user have any control over them, since in many case the
> hypervisor itself is in charge of the naming scheme.

I must admit I didn't think about passed through devices, that is a very good
point. While we could introduce better addressing scheme, it would get more
complicated easily thus ruining the advantages of this approach.

> There's also the issue that allowing arbitrary new names in
> the boot/@target attribute will confuse apps which expect
> it to only have cdrom/floppy/network/hd. It is basically
> changing that attribute from an enumeration, to freeform
> text.

Ah, I should have been explicit about that... It is not changing current
attribute, since we now have <boot dev='fd|hd|cdrom|network'/> and this is
suggesting to use target attribute. So a user/app can decide whether to use
the <boot dev='...'/> style or move to <boot target='...'/> which allows for
better control over boot devices but which is not supported by all
hypervisors.

> I don't entirely like either option in the end since they both
> have negative aspects

Exactly.

> but for sake of compatibility I'd likely have a slight preference for the
> second case.

You are starting to convince me :-)

Jirka