Re: [Qemu-devel] [PATCH v2] virtio-blk: add default serial id

[Stefan Hajnoczi]

On Tue, Oct 09, 2012 at 10:27:26AM +0800, Dave Young wrote:
> On 10/05/2012 04:14 PM, Stefan Hajnoczi wrote:
> 
> > On Sun, Sep 23, 2012 at 10:37:09AM +0800, Dave Young wrote:
> >> For the serial number decreasing issue, I think there's only these two 
> >> ways to
> >> select, there's no ideal way to resolve this issue.
> >> My use case for this is for the kdump kernel to find proper disks,
> >> after 1st kernel crashing 2nd kernel need find right disk to dump vmcore.
> >> In this case v1 and v2 aproaches are both find to me.
> >>
> >> From my point of view, patch v1 is better though, I think unpluging 100000 
> >> is
> >> not a sane use case. It's not likely to happen.
> > 
> > I'm not sure auto-assigning serial numbers is a good idea.  The guest can 
> > use
> > the serial number in /etc/fstab or other places where it expects the serial
> > number to be persistent.
> > 
> > Your patch does not provide persistent serial numbers, so a change to the 
> > QEMU
> > invocation could result in different serial numbers.  The guest will get
> > confused or perhaps refuse to boot.
> 
> 
> Yes, it introduce confusion, but in this way at least the serial number
> can be persistent across guest reboot. Traditionally ide disks use this
> way as well, such as QEMU_HARDISK_00001, I think guest should not use
> this in /etc/fstab.

If you don't want to set a persistent serial number, use another mechanism to
identify the disk.  For example, Linux has /dev/disk/by-path/ which identifies
virtio-blk PCI adapters, IDE, SCSI disks, etc.

Does this work for your use case?

Stefan