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$(index)
> scheme.
>
> Signed-off-by: Viktor Mihajlovski <mihajlov@xxxxxxxxxxxxxxxxxx>
> ---
>
> Actually this is highlighting a larger issue. Apparently QEMU ids
> are limited to a length of 32 bytes. This means that SCSI based
> drives are also in danger to exceed this limit.
> We should consider to use a drive index for controller-attached
> disks for alias generation instead of the verbose
> drive-$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(-)
>
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 879aed8..8c8bef2 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -818,16 +818,8 @@ qemuAssignDeviceHostdevAlias(virDomainDefPtr def, virDomainHostdevDefPtr hostdev
> }
> }
>
> - if (hostdev->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_SCSI) {
> - if (virAsprintf(&hostdev->info->alias, "hostdev-%s-%d-%d-%d",
> - hostdev->source.subsys.u.scsi.adapter,
> - hostdev->source.subsys.u.scsi.bus,
> - hostdev->source.subsys.u.scsi.target,
> - hostdev->source.subsys.u.scsi.unit) < 0)
> - return -1;
> - } else if (virAsprintf(&hostdev->info->alias, "hostdev%d", idx) < 0) {
> + if (virAsprintf(&hostdev->info->alias, "hostdev%d", idx) < 0)
> return -1;
> - }
>
> return 0;
> }
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
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