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

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

Hi,

i wrote:
> > Paolo:
> > May i ask for the favor that you try to add O_RDWR to the qemu_open()
> > call of passthrough devices ?

Paolo Bonzini wrote:
> I think the problem is that you're passing media=cdrom:
> Just do not do that when using scsi-generic.

The result looks promising, indeed. I disabled my hack but left the
first printf active. Now i see at boot time
  block/raw-posix.c: raw_open_common("/dev/sg2", 1000)
  block/raw-posix.c: raw_open_common("/dev/sg2", 1002)
and still no failing ioctls or sense code B 00 06.

Burning to an appendable CD-RW in mode TAO still works. 

So thanks for this swift fulfilling of my wish. :))

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Disappointment: 

CD-RW burning in mode SAO (on a blank medium) gets stuck at this command
  SEND CUE SHEET
  5d 00 00 00 00 00 00 00 20 00 
  To drive: 32b
  41 00 00 01 00 00 00 00 41 01 00 10 00 00 00 00 41 01 01 10
  00 00 02 00 41 aa 01 01 00 00 35 30 

After 200 seconds, the qemu process begins to use 100 % CPU,
and the pacifier messages of xorriso stall. The guest is stuck.

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When i restart qemu and boot the guest without having rebooted the
host, then after about 20 seconds, qemu is at 100 % CPU and no login
is possible. There is a short time window after boot, where i
can log in.

The problem seems to sit in the host's drive /dev/sr1 which
cannot be ejected or used by any program. They all get stuck.
So it is likely that the ungraceful end of drive usage is to blame.

I will tomorrow attach an USB drive to the machine and see
whether re-powering it spares rebooting. (Linux USB is the best
test bed for dangerous drive experiments.)

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So there are still two show stoppers.

DVD+RW gets stuck at SET STREAMING.
(I will hack libburn to avoid this command and check whether
 writing is possible then. Chances are good, as writing an
 already formatted DVD+RW is quite artless.)

CD SAO gets stuck at SEND CUE SHEET.
(SAO is possible with blank CDs only. It is desirable, because its
 results do not show the traditional read-ahead bug of Linux, which
 is caused by the two non-data sectors at the end of TAO tracks.)


Do you have any hints where i should dig for the special processing
of these commands, which obviously suffer timeout after 200 seconds,
and then drive qemu or the guest into a busily unusable state ?

There must be something about them in qemu. On the host they work
flawlessly.
Both send data, but so do SET CD SPEED, MODE SELECT(10), WRITE(10)
which work fine on the guest.
 
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Have a nice day :)

Thomas