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RE: [Xen-devel] SCSI passthrough using /dev/sgX

  • To: <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
  • Date: Tue, 4 Dec 2007 12:40:16 +1100
  • Delivery-date: Mon, 03 Dec 2007 17:42:03 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: Acgxg8KUQjKExGdVRSy6MUZiIZFdLwEkIWvQ
  • Thread-topic: [Xen-devel] SCSI passthrough using /dev/sgX

> Is anyone working on SCSI passthrough using the 'SCSI Generic' support
> under Linux, eg /dev/sgX? This is how VMWare allows a VM to use SCSI
> devices.

I assume that the lack of response means 'no'.

I've just been having a look through the documentation for 'SCSI
Generic' under Linux, and it looks pretty straightforward...

It could be done much like the existing blkdev interface, the 'input'
half of the sg_io_hdr (or something like it), would go on the ring as
the request, and the 'output' half, would come back on the ring as the
response. Buffers would be passed like the block interface does now,
although I'd probably prefer that we allow single byte aligned rather
than 512 byte aligned buffers as the block device currently does, as
Windows tends to use the former a bit. I'm not sure if any other IOCTL's
apart from SG_IO (which is the equivalent of a write + read operation
anyway) would be required as part of normal IO, they could just be
performed at initialisation and written to xenstore.

This would allow single SCSI devices or pretty much any type to be
exported to domains.

I'm interested in writing the Linux backend, and the Windows front end
as I'm pretty desperate for tape drive passthrough...




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