Re: [Xen-devel] [PATCH] Support for official xvd major number

[Jeremy Katz <katzj@xxxxxxxxxx>]

On Thu, 2005-07-14 at 22:38 +0100, Keir Fraser wrote:
> On 14 Jul 2005, at 22:35, Jeremy Katz wrote:
> > Also, on a side note that is really unrelated to the patch, is there
> > really a good reason why these hoops are still gone through instead of
> > having the kernel allocate the next disk instead of the hard-coding 
> > with
> > things somewhat out of order and stealing the major/minors of other
> > subsystems?
> 
> I'm not sure what you mean? Specifying device numbers up front in a 
> config file means that you know e.g., what device names to put in your 
> fstab and what to specify as your rootfs device. 

Your first disk should get registered first and be xvda, your second
xvdb, etc.  If you're afraid of the order changing, you should be using
label or uuid to mount.  The same questions come up with physical
devices.

> And stealing scsi/ide 
> device names/numbers is the strategy of least surprise to userspace 
> tools and scripts (e.g., some vendor init scripts have a baby if 
> filesystems are mounted on a weirdly-named block device like xvd<foo>). 

Those scripts are broken and are going to break with a fair bit of other
hardware too.  There are more of these "weird" block devices being added
and not less.  And as it stands now, if something sees "scsi disk" and
then tries to do any checks with /proc/scsi, they're going to fail.  So
there are common things that get broken with both.

Jeremy


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