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Re: [Qemu-devel] Re: [PATCH] virtio-blk: assign a default serial number
From: |
Ryan Harper |
Subject: |
Re: [Qemu-devel] Re: [PATCH] virtio-blk: assign a default serial number if none provided |
Date: |
Wed, 2 Jun 2010 07:26:22 -0500 |
User-agent: |
Mutt/1.5.6+20040907i |
* Michael S. Tsirkin <address@hidden> [2010-06-02 06:59]:
> On Wed, Jun 02, 2010 at 06:45:46AM -0500, Ryan Harper wrote:
> > * Michael S. Tsirkin <address@hidden> [2010-06-02 04:08]:
> > > On Tue, Jun 01, 2010 at 08:48:54PM -0500, Ryan Harper wrote:
> > > > This patch applies on-top of John's virtio-blk serial patches.
> > > >
> > > > Generate default serial numbers for virtio drives based on
> > > > DriveInfo.unit which is
> > > > incremented for each additional virtio-blk device. This provides a
> > > > per-virtio-blk number to use in the default string: QM%05d that is used
> > > > in
> > > > hw/ide/core.c. The resulting serial number looks like: QM00001, etc.
> > > >
> > > > Signed-off-by: Ryan Harper <address@hidden>
> > >
> > >
> > > I think that there's a problem with this approach in that hot plug A,
> > > hot plug B, hot unplug A is not the same as hot plug B.
> > > So you might get guest boot failures and no easy way to
> > > figure out why. For guests that need S/N, I think they
> > > really must be persistent.
> >
> > That's true; though I think most boot drives boot via either LVM or UUID
> > which will remain persistent. That said, if you are relying on the
> > by-id; then of course the user will need to specify serial versus having
> > one auto-generated.
>
> I guess the question then would be, if you don't rely on the S/N, why
> do you want to set it?
Functional similarity; we have default serial numbers for ide and scsi.
scsi is hotpluggable and would suffer the same issue; and of course ide
doesn't do hotplug. I don't think most folks will encounter the above
scenario and that having the same default serial numbers being generated
like we do ide and scsi is reasonable.
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
address@hidden