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

[Stefan Hajnoczi <stefanha@gmail.com>]

On Tue, Nov 1, 2011 at 9:03 PM, Thomas Schmitt <scdbackup@gmx.net> wrote:
> Hi,
>
> Stefan Hajnoczi wrote:
>> 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.
>
> Ok. I'll forward my original mail and this reply to qemu-devel.
>
>
>> The current state is that CD-ROM passthrough with virtio-scsi does not
>> work yet because the in-kernel SCSI target needs a patch to allow the
>> GET EVENT STATUS NOTIFICATION command which newish Linux kernel use to
>> poll CD-ROMs.
>
> I have the exploration of this command on my own TODO list.
> Good to know that it might make problems in the kernel.
>
> --------------------------------------------------------------------------
>
>> In theory QEMU with -drive file=/dev/sg0,if=scsi,... should provide
>> SCSI passthrough.  QEMU is a userspace process so it uses the
>> scsi-generic driver to pass through SCSI commands.  You could try that
>> (note this is without virtio-scsi and should work today in theory).
>
> The following experiments show quite ill effects.
>
> I could need instructions how to install and use qemu from git
> on Debian GNU/Linux 6.0.2 without disturbing the installed
> qemu-0.12.5 from apt-get.
>
> Currently i run 0.15.1 from release tarball as
>  ./qemu-0.15.1/i386-softmmu/qemu
> with no special indication that this would cause the problems.
> The installed 0.12.5 capsizes at the same occasionsi, albeit with
> different symptoms.
>
> Nevertheless i get a message at startup
>  Could not open option rom 'sgabios.bin': No such file or directory
> which indicates that this is not the intended way to have a qemu
> for testing.
> So when i get a git clone, it would be best to have a more
> conventional test setup. (Be it only for kvm acceleration.)

If you want to ensure a self-contained environment try:
qemu-0.15.1/i386-softmmu/qemu -L qemu-0.15.1/pc-bios ...

The -L option sets QEMU's "data_dir" which is used as the base
directory.  There is code to auto-detect but it will prefer the
system-wide /usr/share/qemu path instead of ../pc-bios, so explicitly
setting this option is the right thing to do.

>
> --------------------------------------------------------------------------
>
> First try is on qemu-0.15.1:
>
>  ./qemu-0.15.1/i386-softmmu/qemu \
>     -nographic \
>     -m 512 \
>     -net nic,model=ne2k_pci \
>     -net user,hostfwd=tcp::5557-:22 \
>     -hda /dvdbuffer/i386-install.qemu \
>     -drive file=/dev/sg2,if=scsi,bus=4,unit=0,media=cdrom
>
> Now i have two drives by one option.
> xorriso -devices reports
>  0  -dev '/dev/sr0' rwrw-- :  'TSSTcorp' 'CDDVDW SH-S223B'
>  1  -dev '/dev/sr1' rwrw-- :  'QEMU    ' 'QEMU DVD-ROM'
> with /dev/sr1 being an empty drive. (Is this a known bug ?)

Off the top of my head I'd say this is an empty IDE CD-ROM drive which
is added by default.  Would need to check the code to be sure though.

> But /dev/sr0 seems to work well, on the first glimpse.
>
> Trying to burn something, being logged in via SSH
>
>  $ xorriso -dev /dev/sr0 -add /usr/lib
>
> reads old session, adds files, but when writing should begin:
>
>  Connection to localhost closed by remote host.
>  Connection to localhost closed.
>
> and i get the host system prompt.
>
> The window where i ran qemu says:
>
>  qemu: ./qemu_dir/qemu-0.15.1/hw/lsi53c895a.c:540:
>        lsi_do_dma: Assertion `s->current' failed.

That's a bug in the LSI SCSI HBA emulation or a generic SCSI emulation
problem in QEMU.  I have CCed Paolo and Kevin who have recently been
working on SCSI and IDE much more than me and know more.

> With the installed qemu-0.12.5:

Thanks for the extensive testing.  I actually suggest focussing just
on qemu.git/master because that is where developers mostly invest
their time.  The data points on older versions can be interesting but
my guess is folks won't have time to debug them - instead let's make
qemu.git/master work.

Stefan