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

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> does SCSI passthrough need hardware support ,such as VT-d, or not?if
> there are two device and two VMs, does it need VT-d support, or not ?
> can it run in PVmode or have to run in HVM mode?

The SCSI passthrough code that I was talking about is a paravirtualised 
front / back driver, so it doesn't use VT-d.  I don't think it is currently 
supported under HVM guests.

Cheers,
Mark

> Thanks in advance
>
> Mark Williamson åé:
> > There are some folks (from Fujitsu?  I think?) who are working on
> > front/back-based SCSI passthrough.  Patches have been submitted several
> > times but not merged yet.  They'll be in the list archives...
> >
> > I don't think they've done a Windows frontend though ;-)
> >
> > Cheers,
> > Mark
> >
> > On Tuesday 04 December 2007, James Harper wrote:
> >>> 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...
> >>
> >> Comments?
> >>
> >> Thanks
> >>
> >> James
> >>
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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