Il 23/08/2012 12:08, Stefan Hajnoczi ha scritto:

quoted

I'm still trying to understand the extent of the problem.

The problem occurs for _USB_ CD-ROMs according to Ben.  Passthrough of
USB storage devices should be done via USB passthrough, not virtio-scsi.
 If we do USB passthrough via the SCSI layer we miss on all the quirks
that the OS may do based on the USB product/vendor pairs.  There's no
end to these, and some of the quirks may cause the device to lock up or
corruption.

I'd rather see a reproducer using SAS/ATA/ATAPI disks before punting.

This issue affects passthrough: either an entire sg device or at least
a SG_IO ioctl (e.g. a non-READ/WRITE SCSI command).

To reproduce it, check host queue limits and guest virtio-scsi queue
limits.  Then pick a command that can exceed the limits and try it
from inside the guest :).

Yes, so much is clear.  But does it happen _in practice_?  Do initiators
actually issue commands that are that big?

Paolo