On Wed, Oct 10, 2012 at 10:07:01AM +0800, Dave Young wrote: > On 10/09/2012 04:31 PM, Stefan Hajnoczi wrote: > > > 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? > > > I have tried this before, but after rebooting (kexec/kdump) the by-path > link was not created. It might be udev bug anyway, I'm not sure though.
Yes, it's udev. Check /lib/udev/rules.d/60-persistent-storage.rules. Stefan