Re: [Qemu-devel] [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive

[Paolo Bonzini]

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