Re: [libvirt] [RFC PATCH] qemu: Shorten SCSI hostdev alias to avoid QEMU failure

On Fri, Jul 12, 2013 at 05:13:56PM +0200, Viktor Mihajlovski wrote: > The alias for hostdevs of type SCSI can be too long for QEMU if > larger LUNs are encountered. Here's a real life example: > > <hostdev mode='subsystem' type='scsi' managed='no'> > <source> > <adapter name='scsi_host0'/> > <address bus='0' target='19' unit='1088634913'/> > </source> > <address type='drive' controller='0' bus='0' target='0' unit='0'/> > </hostdev> > > this results in a too long drive id, resulting in QEMU yelling > > Property 'scsi-generic.drive' can't find value 'drive-hostdev-scsi_host0-0-19-1088634913' > > This commit changes the alias back to the default hostdev$(index) > scheme. > > Signed-off-by: Viktor Mihajlovski <mihajlov(a)linux.vnet.ibm.com&gt; > --- > > Actually this is highlighting a larger issue. Apparently QEMU ids > are limited to a length of 32 bytes. This means that SCSI based > drives are also in danger to exceed this limit. > We should consider to use a drive index for controller-attached > disks for alias generation instead of the verbose > drive-$bustype-$busaddress schema. Urgh that sucks. I had no idea QEMU would impose such an arbitrary length limitation for something like this. > > src/qemu/qemu_command.c | 10 +--------- > .../qemuxml2argv-hostdev-scsi-boot.args | 4 ++-- > .../qemuxml2argv-hostdev-scsi-lsi.args | 4 ++-- > .../qemuxml2argv-hostdev-scsi-readonly.args | 4 ++-- > .../qemuxml2argv-hostdev-scsi-virtio-scsi.args | 4 ++-- > 5 files changed, 9 insertions(+), 17 deletions(-) >

ACK There's no back compatibility issues, since we store the aliases for running guests in the state XML. Thus this will only affect newly launched guests Daniel