[linux-target-packaging] Bug#880576: targetcli-fb: Cannot create PSCSI backend for SCSI tape drive

[Christian Seiler]

Control: tags -1 + confirmed upstream

Hi,

On 11/02/2017 02:29 PM, Herbert Nachtnebel wrote:
> exporting a local SCSI tape drive using targetcli is not possible. The used
> SCSI tape
> drive is an older HP Ultrium-2 SCSI drive connected via a Adaptec 29320ALP U320
> PCIe
> SCSI controller to the host.  The host is a freshly set up Debian 9.2 system.

Thanks for the detailed bug report! Unfortunately I don't have a SCSI
tape drive with which I can test this (I only have disks and CD drives,
which do work according to your report), so I can't reproduce this
myself.

That said, I've looked at the code, and the current pscsi interface
in the targetcli GUI can only export block devices, but tape drives
are actually character devices - that's why it doesn't find anything,
because it looks for devices in /sys/block in the sysfs structure, and
the tape drive doesn't exist there.

Now I'm not currently sure whether this is just a but in targetcli
because it assumes block devices and that tape device export would
actually work on the kernel side, or if this also has problems with
the kernel.

Could you perhaps try to add this manually via the configfs interface?

1. Ensure that rtslib-fb-targetctl.service is started. (To make sure
   the configfs filesystem for LIO is mounted.)

2. Run the following commands to try to create the backstore manually:

# Create backstore ('tape' is just the name here, you can also call
# it something else if you like; the other part of the path is fixed
# though)
mkdir -p /sys/kernel/config/target/core/pscsi_0/tape

# Generate a unique WWN
uuidgen > /sys/kernel/config/target/core/pscsi_0/tape/wwn/vpd_unit_serial

# Add the device (IDs taken from your lsscsi output)
echo scsi_host_id=2,scsi_channel_id=0,scsi_target_id=0,scsi_lun_id=0 \
     > /sys/kernel/config/target/core/pscsi_0/tape/control

# Enable the backstore
echo 1 > /sys/kernel/config/target/core/pscsi_0/tape/enable

# Check kernel logs
# Check 'targetcli ls' output

If that works and the device is added you _should_ be able to export
it via targetcli. If that also works you should be able to use the
tape device from an iSCSI initiator.

What most likely won't work is targetctl being able to reload the
configuration when the system reboots, so this is only temporary. [1]

But if the export of the device actually does work on your system I
could create a patch for targetctl (and possibly targetcli) that
should fix this, and if that does work I'll ask the release team
whether I can get that into the next point release of Stretch.

Regards,
Christian

[1] Note: targetctl is the command used to restore configuration at
    boot, targetcli is the shell to configure it.