[Qemu-devel] Do you have a use for a tester of virtio-scsi with CD drives ?

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i sent the following to Paolo Bonzini and Stefan Hajnoczi.

Stefan advised
> In the future I think it's appropriate to CC qemu-devel since others
> in the community may be interested in virtio-scsi discussions too.

So i forward my mail to this list.
I am subscribed now.

A first test report of SCSI passthrough without virtio-scsi will
follow soon.

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Hi,

being unsure whether my cause is appropriate for qemu-devel list,
i write directly to you, who recently discussed virtio-scsi on that
list. If there is a better place, please direct me to it.

I would like to participate as tester in the development of virtio-scsi.
In the october 2011 archive of qemu-devel list, i found a link to
  http://wiki.qemu.org/Features/VirtioSCSI
with
  Status: Under development. Not ready for real-world use yet.
  Features: [...] SCSI passthrough
Is there an outlook when it will be ripe for testing SCSI transactions
with CD-ish drives ?

My goal is to operate a real DVD burner drive from within a Debian
GNU/Linux 6.0.3 i386 as guest on a Debian GNU/Linux 6.0.2 amd64.
The SCSI commands are transported by the guest system via ioctl(SG_IO).
Burn program is xorriso, which uses libburn to communicate with
the drive. I am developer of both, but quite a newbie when it comes
to virtual machines.

I have SCSI specs SPC, SBC, MMC, and some experience in reading and
applying them. I can test with DVD drives at IDE/ATAPI, SATA, and USB
on real installations of GNU/Linux, FreeBSD 8 and OpenSolaris svn 134.
No experience with kernel programming or bus hardware issues.
(libburn is an MMC driver in userspace.)

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What i tried so far:

The qemu version of Debian 6.0.2 is 0.12.5. So i also built 0.15.1 from
the release tarball. I experienced no different behavior, though.

I tried
  -drive file=/dev/sr1,if=virtio,media=cdrom
which yields the same results as -drive if=scsi. (See below.)
Especially the emulated drive identifies itself as
  vendor 'QEMU' product 'QEMU DVD-ROM' revision '0.15'
rather than
  vendor 'TSSTcorp' product 'CDDVDW SH-S223B' revision 'SB02'
of the real one.
Obviously i do not get SCSI passthrough here.

Before this i tried
  -cdrom /dev/sr1
The emulated QEMU DVD-ROM rev 0.12 and rev 0.15 expectedly turned out
to be usable for reading only.

With
  -drive file=/dev/sr1,if=scsi,bus=4,unit=0,media=cdrom
the emulated QEMU DVD-ROM has similar restrictions as with -cdrom,
and additionaly states that there is no medium loaded.
E.g. with this SCSI transaction:
  TEST UNIT READY
  00 00 00 00 00 00 
  +++ sense data = F0 00 02 00 00 00 00 0A 00 00 00 00 3A 00 00 00 00 00
  +++ key=2  asc=3Ah  ascq=00h   (     4 ms)
The block device driver of GNU/Linux sees no medium either:
  dd: opening `/dev/sr0': No medium found
This happens with real /dev/sr1 and with an ISO image in a regular file.

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Have a nice day :)

Thomas