[PATCH 0/6] qemu: Fix cdrom as SCSI hostdev via -blockdev

[Peter Krempa]

On Tue, Oct 20, 2020 at 14:10:12 +0200, daggs wrote:
> Greetings Peter,
> 
> > Sent: Tuesday, October 20, 2020 at 3:00 PM
> > From: "Peter Krempa" <pkrempa at redhat.com>
> > To: "daggs" <daggs at gmx.com>
> > Cc: libvir-list at redhat.com
> > Subject: Re: [PATCH 0/6] qemu: Fix cdrom as SCSI hostdev via -blockdev
> >
> > [...]
> >
> > try 'ls -lia /sys/bus/scsi/devices' that has all the data
> >
> >
> 
> $ ls -lia /sys/bus/scsi/devices
> total 0
>    7017 drwxr-xr-x    2 root     root             0 Oct 20 11:11 .
>    7015 drwxr-xr-x    4 root     root             0 Oct 20 11:11 ..
>   17968 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host0 -> ../../../devices/pci0000:00/0000:00:1f.2/ata1/host0
>   18016 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host1 -> ../../../devices/pci0000:00/0000:00:1f.2/ata2/host1
>   18064 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host2 -> ../../../devices/pci0000:00/0000:00:1f.2/ata3/host2
>   18112 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host3 -> ../../../devices/pci0000:00/0000:00:1f.2/ata4/host3
>   18160 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host4 -> ../../../devices/pci0000:00/0000:00:1f.2/ata5/host4
>   18208 lrwxrwxrwx    1 root     root             0 Oct 20 11:11 host5 -> ../../../devices/pci0000:00/0000:00:1f.2/ata6/host5

Oh, so your guest OS doesn't seem to recognize virtio-scsi apparently!

On my test VM I've got the following:

$ ls -lia /sys/bus/scsi/devices
total 0
 5659 drwxr-xr-x. 2 root root 0 Oct 19 17:34 .
 5657 drwxr-xr-x. 4 root root 0 Oct 19 17:34 ..
18418 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 0:0:0:0 -> ../../../devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0
20322 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 6:0:0:1 -> ../../../devices/pci0000:00/0000:00:02.7/0000:08:00.0/virtio6/host6/target6:0:0/6:0:0:1
19773 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 6:0:0:3 -> ../../../devices/pci0000:00/0000:00:02.7/0000:08:00.0/virtio6/host6/target6:0:0/6:0:0:3
15523 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host0 -> ../../../devices/pci0000:00/0000:00:1f.2/ata1/host0
15571 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host1 -> ../../../devices/pci0000:00/0000:00:1f.2/ata2/host1
15619 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host2 -> ../../../devices/pci0000:00/0000:00:1f.2/ata3/host2
15667 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host3 -> ../../../devices/pci0000:00/0000:00:1f.2/ata4/host3
15715 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host4 -> ../../../devices/pci0000:00/0000:00:1f.2/ata5/host4
15763 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host5 -> ../../../devices/pci0000:00/0000:00:1f.2/ata6/host5
19403 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 host6 -> ../../../devices/pci0000:00/0000:00:02.7/0000:08:00.0/virtio6/host6
18376 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 target0:0:0 -> ../../../devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0
19733 lrwxrwxrwx. 1 root root 0 Oct 19 17:34 target6:0:0 -> ../../../devices/pci0000:00/0000:00:02.7/0000:08:00.0/virtio6/host6/target6:0:0

You can see that host6 is a virtio-scsi controller and it has targets.

You need to figure out why your guest doesn't have the driver.
Alternative would be to use a different scsi controller model, but any
emulated will result in overhead, so the best solution will be to get
drivers.

Sorry I've mislead you with the initial red herring, but your report
really came after I've modified how we do hostdevs so I thought I messed
up something.