RE: Disk naming (Was Re: [Xen-devel] [PATCH] Guest boot loadersupport [1/2])

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> On Thu, 2005-04-14 at 14:22 -0400, Philip R Auld wrote:
> > As a slight but related digression, has any thought been given to 
> > using something other than /dev/[hs]d* names for specifying block 
> > devices? The name /dev/sdb only has meaning for the current 
> state of 
> > the running dom0 OS. It may not mean the same device on a different 
> > dom0. This can lead to problems in say migration.
> > In fact, it may not be the same when the domain is restored locally.
> 
> To be even slightly more radical, I don't think that for the 
> guests, the vbds should be being exposed as SCSI or IDE since 
> they're not.  By being presented as such, there's a set of 
> assumptions about ioctls and behaviors which aren't the case 
> for disks on blkfront.  Even with all of the pain using your 
> own major/minor for a disk device is, I think it probably is 
> the right thing to do.  And I've added the code to 
> parted/lvm2/.../etc enough to be able to do it in my sleep 
> this point if this route is taken :)

I don't think there's a huge problem with exposing vbd's as sdX/hdX
within a guest. We used to have our own xdX device, but it just broke
too much stuff, hence we hijacked had/sda. I haven't seen too many
problems with ioctls.

I think the key issue is that in domain configs, you want to specify the
source of the vbd in some high-level name and have the control tools do
the necessary to map it to a local device and then export it. This
already happens with file: disk paths. We just need something similar
for iscsi.

Ian

 

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