Re: [Xen-devel] pvops xen_blkfront does not enforce device names

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 29 Apr 2016, Konrad Rzeszutek Wilk wrote:
> On Fri, Apr 29, 2016 at 01:29:17AM -0600, Jan Beulich wrote:
> > >>> On 29.04.16 at 08:45, <konrad.wilk@xxxxxxxxxx> wrote:
> > > On Tue, Apr 26, 2016 at 03:28:45PM +0200, Olaf Hering wrote:
> > >> Why does xen_blkfront not enforce kernel device names from domU.cfg?
> > >> In my PV domU.cfg I still have something like this:
> > >> disk=[ 'file:/path,hda,w' ]
> > >> 
> > >> With pvops and xen_blkfront I get xvda.
> > >> With xenlinux and xenblk I get hda.
> > > 
> > > It has no business subverting the hda device names which
> > > are specifically for legacy devices.
> > 
> > That's one view. The other is that people moving from XenoLinux to
> > pv-ops are in trouble without it. How did you (or Citrix, if anyone of
> > them looks) deal with this when doing the transition?
> 
> We had transition folks to use 'UUID' or volume group names in their 'root='
> entry so never had an issue with this.
> > 
> > > [We got smacked down at some point for having done this]
> > 
> > In which way?
> 
> For usurping the 'hda'. Stefano may remember the details more..

The argument goes as follow: 'hda' as 'xvda' or 'sda' are Linux specific
names. A different operating system could name its devices 'goofy', or
any other made up names. The Xen toolstack has no business in choosing
the naming scheme for the guest kernel to use. Moreover xl can do
nothing to enforce it: what if the OS stubbornly keeps calling its
devices 'goofy' even if according to xl should be 'hda'? It is just an
internal OS representation, so the OS can do as it wishes.

Linux doesn't want to call PV disks anything else than xvd*. After all
they are PV disks, aren't they? And Xen cannot do anything about it.

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