Re: [Xen-devel] Greater than 16 xvd devices for blkfront

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Thu, May 08, 2008 at 11:14:34PM +0100, Jeremy Fitzhardinge wrote:
> Chris Wright wrote:
> >Well, we don't actually need 202, or any minor numbers at all.  The major
> >is only needed for the case where xvd masquerades as IDE or SCSI.
> >We ripped this wart out for upstream Linux. 
> 
> I'm considering putting it back in if it makes anyone's life easier.  In 
> general using labels/uuids is the best way to make an installation 
> device-agnostic, but installers might have an easier time with a forged 
> scsi device or something.  I mentioned it in passing to Al Viro, and he 
> was surprisingly non-insulting about the notion.
> 
> > And the guest can happily
> >dynamically allocate minor numbers on its own behalf.  A disk discovery
> >event can be completely dynamic, the admin just wouldn't be able to
> >guarantee which minor slot gets allocated for a particular disk in
> >a guest.  We do have mount by label or UUID.
> >  
> 
> That's true for filesystems which have already been initialized.  But if 
> you're attaching 4 new devices to a guest and they appear at random 
> device nodes, how do you know which is which?  Smell?

Well there's /dev/disk/by-{path,id}. Now there's no udev rules to setup
these links for Xen VBD (afaik), but we could arrange to have some suitable
info used to provide a persistent path under either of those locations.

Dan.
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