Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support

From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Christoph Hellwig <hch@lst.de>,
	Rusty Russell <rusty@rustcorp.com.au>,
	qemu-devel@nongnu.org, kvm@vger.kernel.org,
	Hannes Reinecke <hare@suse.de>
Subject: Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support
Date: Tue, 28 Apr 2009 18:52:13 +0200	[thread overview]
Message-ID: <200904281852.13916.borntraeger@de.ibm.com> (raw)
In-Reply-To: <49F730AD.8090705@codemonkey.ws>

Am Tuesday 28 April 2009 18:37:01 schrieb Anthony Liguori:
> Christoph Hellwig wrote:
> >> Should we be 
> >> handling some SCSI cmds internally to QEMU (like eject operations) and 
> >> supporting media=cdrom in -drive for if=virtio?
> >>     
> >
> > Not quite yet.  Eventually I want to support a virtio-scsi kind of
> > transport which would use the same virtio-blk protocol but only send
> > scsi commands.  We'd need a different driver on the Linux side for
> > it that registers to the scsi layer.  On the QEMU side it could either
> > do pass-through to a real scsi device using SG_IO or use the existing
> > command scsi emulator in scsi-disk.c.
> >   
> 
> Ah, excellent.  I think that's a great thing to do.  So do you think 
> virtio-scsi would deprecate virtio-blk?

There are lots of other block device drivers with strange characteristics. 
For example dasd/xpram disks with 4k block size or other disks with strange partitioning schemes. Doing a scsi emulation on top of these beasts looks possible but far from ideal. So I guess we will need virtio_blk for non-scsi block devices.

Christian