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

[Thomas Schmitt]

Hi,

i wrote:
> > The sense code is listed in MMC as:
> >    B 00 06 I/O PROCESS TERMINATED

Paolo Bonzini wrote:
> Is it good or bad? :)  I see it even in the very first command.

It does not indicate success. MMC only has the meager info above.

SPC-3 says in table 27 about sense key B:
 "Bh : ABORTED COMMAND: Indicates that the device server aborted
  the command. The application client may be able to recover by
  trying the command again."

It does not come from the real drive, i am very sure.
So unless you find a particular reason in qemu, i doubt that repetition
will help.


> What do these give on the host?  Sounds like another LSI emulation bug.

All is well with the drive on the host.
This is my test machine, which checks build and function of xorriso
with GNU/Linux, FreeBSD 8, and OpenSolaris. It also tested the
freshly released libcdio-0.83 by Rocky Bernstein which uses
on Linux ioctl(CDROM_SEND_PACKET) rather than ioctl(SG_IO).

When i had trouble with vanishing udev links on Debian 6.0.2,
i also tested with wodim. It worked as good as can be expected.


> > The current release 1.1.6 will not recognize QEMU DVD-ROM because
> > of its inconsistent Mode Page 2Ah with short Page Length (18 decimal).

> The page length is indeed 18 for IDE and 20 for SCSI.  I made some changes
> to that page recently, but left the 18 because I feared causing regression.
> But if that is a bug, we can probably fix it in 1.0.

This riddles me.
In hw/scsi-disk.c:mode_sense_page() i see that the page 0x2A
(now MODE_PAGE_CAPABILITIES) gets filled with 22 bytes, compliant
to MMC-1. (Later MMCs have longer minimum sizes.)
But libburn receives only 20 of them, because the Page Length
is reported as 0x12 in the 10th byte of the reply:
  MODE SENSE
  5a 00 2a 00 00 00 00 00 1c 00
  From drive: 28b
  00 22 70 00 00 00 00 00 2a 12 00 00 71 60 29 00 02 c2 00 02
  02 00 02 c2 00 00 00 00
Nevertheless i see in hw/scsi-disk.c
  p[1] = 0x14;
So how is this altered to 0x12 in the further course of processing ?

Further, the Mode Data Length is 0x22, announcing 34 + 2 = 36 overall
bytes in the reply, which matches neither Page Length 0x12 nor 0x14,
but would match Page Length 26 decimal = 0x1a.

A real DVD-ROM drive ('HL-DT-ST' 'DVD-ROM GDR8162B') rather tells
  MODE SENSE
  5a 00 2a 00 00 00 00 00 1c 00
  From drive: 28b
  00 20 41 00 00 00 00 00 2a 18 3f 00 71 73 2b 23 21 13 01 00
  01 00 0d c8 00 00 00 00
so that libburn repeats the transaction with adjusted Allocation Length
  MODE SENSE
  5a 00 2a 00 00 00 00 00 22 00
  From drive: 34b
  00 20 41 00 00 00 00 00 2a 18 3f 00 71 73 2b 23 21 13 01 00
  01 00 0d c8 00 00 00 00 00 00 00 01 00 00

(Some Linux transports react badly if the Allocation Length surpasses
 the actually available amount of bytes. So i adopted this two-step
 strategy, which i learned from growisofs by Andy Polyakov.)


> > Is it a known bug that 'QEMU DVD-ROM' is always empty if it stems
> > from option -drive if=scsi ?
> No, it is not a bug.  Remember this is an IDE DVD-ROM.  It is not
> instantiated by -drive if=scsi: it is the same device that -cdrom crsates,

You are the expert. So i do not contradict.

But it behaves differently. The devices created by -cdrom do have
a medium loaded. The 'QEMU DVD-ROM' from -drive if=scsi have no medium.
(But the other drive 'CDDVDW SH-S223B' from -drive file=/dev/sg1,if=scsi
 has a medium and replies the same as on the host system.)

I just checked with the git clone.
Readable are
  -cdrom /dev/sr0
  -cdrom /dvdbuffer/pseudo_drive  (a regular file)
with dd and with xorriso (via guest SG_IO).

No medium is found in
  -drive file=/dev/sr0,if=scsi,media=cdrom
  -drive file=/dvdbuffer/pseudo_drive,if=scsi,media=cdrom
which report like the /dev/sg1 based 'QEMU DVD-ROM':

No current profile (00 00 in bytes 6 and 7 of reply):
  GET CONFIGURATION
  46 00 00 00 00 00 00 00 14 00 
  From drive: 20b
  00 00 00 10 00 00 00 00 00 00 03 08 00 10 00 00 00 08 00 00

Error condition 2 3A 00 MEDIUM NOT PRESENT on
  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)


> try inspecting /dev/disk and sysfs.  The ATAPI and SCSI code is
> indeed very similar and will be even more similar in 1.0, but for now they
> are distinct.

They are not easy to distinguish since /dev/hdX passed the way.

  $ ls /dev/disk
  ata-QEMU_HARDDISK_QM00001        scsi-SATA_QEMU_HARDDISK_QM00001
  ata-QEMU_HARDDISK_QM00001-part1  scsi-SATA_QEMU_HARDDISK_QM00001-part1
  ata-QEMU_HARDDISK_QM00001-part2  scsi-SATA_QEMU_HARDDISK_QM00001-part2
  ata-QEMU_HARDDISK_QM00001-part5  scsi-SATA_QEMU_HARDDISK_QM00001-part5

With the "-part" suffixes, this does not look like a DVD+RW,
which always only has one logical track.

  $ ls -l /sys/bus/scsi/devices
  total 0
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 0:0:0:0 -> 
../../../devices/pci0000:00/0000:00:01.1/host0/target0:0:0/0:0:0:0
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 1:0:0:0 -> 
../../../devices/pci0000:00/0000:00:01.1/host1/target1:0:0/1:0:0:0
  lrwxrwxrwx 1 root root 0 Nov  2 18:35 2:0:0:0 -> 
../../../devices/pci0000:00/0000:00:04.0/host2/target2:0:0/2:0:0:0
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 host0 -> 
../../../devices/pci0000:00/0000:00:01.1/host0
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 host1 -> 
../../../devices/pci0000:00/0000:00:01.1/host1
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 host2 -> 
../../../devices/pci0000:00/0000:00:04.0/host2
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 target0:0:0 -> 
../../../devices/pci0000:00/0000:00:01.1/host0/target0:0:0
  lrwxrwxrwx 1 root root 0 Nov  2 18:30 target1:0:0 -> 
../../../devices/pci0000:00/0000:00:01.1/host1/target1:0:0
  lrwxrwxrwx 1 root root 0 Nov  2 18:35 target2:0:0 -> 
../../../devices/pci0000:00/0000:00:04.0/host2/target2:0:0

  $ cat /proc/scsi/sg/device_hdr /proc/scsi/sg/devices
  host    chan    id      lun     type    opens   qdepth  busy    online
  0       0       0       0       0       1       1       0       1
  1       0       0       0       5       1       1       0       1
  2       0       0       0       5       1       1       0       1
  address@hidden:~> cat /proc/scsi/sg/device_strs
  ATA             QEMU HARDDISK           0.15
  QEMU            QEMU DVD-ROM            0.15
  TSSTcorp        CDDVDW SH-S223B         SB02

This is inconclusive, as it lists the hard disk too.

Whatever the reason, there is a problem with -drive if=scsi,medium=cdrom.


Have a nice day :)

Thomas