[root@arch-zfs-test ~]# journalctl -f
-- Logs begin at Sat 2017-04-15 01:20:58 EEST. --
May 03 14:54:03 arch-zfs-test systemd[1496]: Starting D-Bus User Message Bus Socket.
May 03 14:54:03 arch-zfs-test systemd[1496]: Reached target Timers.
May 03 14:54:03 arch-zfs-test systemd[1496]: Reached target Paths.
May 03 14:54:03 arch-zfs-test systemd[1496]: Listening on D-Bus User Message Bus Socket.
May 03 14:54:03 arch-zfs-test systemd[1496]: Reached target Sockets.
May 03 14:54:03 arch-zfs-test systemd[1496]: Reached target Basic System.
May 03 14:54:03 arch-zfs-test systemd[1496]: Reached target Default.
May 03 14:54:03 arch-zfs-test systemd[1496]: Startup finished in 32ms.
May 03 14:54:03 arch-zfs-test systemd[1]: Started User Manager for UID 0.
May 03 14:54:03 arch-zfs-test login[1491]: ROOT LOGIN ON hvc0

# After the 1st `xl block-attach` command:

May 03 15:03:44 arch-zfs-test kernel: xen-blkback: backend/vbd/0/51712: using 4 queues, protocol 1 (x86_64-abi) persistent grants
May 03 15:03:44 arch-zfs-test kernel: xen-blkback: backend/vbd/0/51712: using 4 queues, protocol 1 (x86_64-abi) persistent grants
May 03 15:03:44 arch-zfs-test root[1569]: /etc/xen/scripts/block: add XENBUS_PATH=backend/vbd/0/51712
May 03 15:03:44 arch-zfs-test root[1621]: /etc/xen/scripts/block: Writing backend/vbd/0/51712/physical-device e6:0 to xenstore.
May 03 15:03:44 arch-zfs-test root[1623]: /etc/xen/scripts/block: Writing backend/vbd/0/51712/physical-device-path /dev/zd0 to xenstore.
May 03 15:03:44 arch-zfs-test root[1630]: /etc/xen/scripts/block: Writing backend/vbd/0/51712/hotplug-status connected to xenstore.

# After the 2nd `xl block-attach` command:

May 03 15:05:37 arch-zfs-test kernel: xen-blkback: backend/vbd/0/51728: using 1 queues, protocol 1 (x86_64-abi) persistent grants
May 03 15:05:37 arch-zfs-test kernel: xen-blkback: backend/vbd/0/51728: using 1 queues, protocol 1 (x86_64-abi) persistent grants
May 03 15:05:37 arch-zfs-test root[1655]: /etc/xen/scripts/block: add XENBUS_PATH=backend/vbd/0/51728
May 03 15:05:37 arch-zfs-test root[1709]: /etc/xen/scripts/block: Writing backend/vbd/0/51728/physical-device e6:20 to xenstore.
May 03 15:05:37 arch-zfs-test root[1711]: /etc/xen/scripts/block: Writing backend/vbd/0/51728/physical-device-path /dev/zd32 to xenstore.
May 03 15:05:37 arch-zfs-test root[1715]: /etc/xen/scripts/block: Writing backend/vbd/0/51728/hotplug-status connected to xenstore.

# After the 1st `xl block-detach` command:

May 03 15:06:43 arch-zfs-test root[1730]: /etc/xen/scripts/block: remove XENBUS_PATH=backend/vbd/0/51712

# After the 2nd `xl block-detach` command:

May 03 15:08:09 arch-zfs-test kernel: traps: xl[1400] general protection ip:7f00df92b19d sp:7fff97ba7040 error:0
May 03 15:08:09 arch-zfs-test kernel:  in libxenlight.so.4.8.0[7f00df8fe000+dd000]
May 03 15:08:09 arch-zfs-test systemd[1]: Created slice system-systemd\x2dcoredump.slice.
May 03 15:08:09 arch-zfs-test systemd[1]: Started Process Core Dump (PID 1740/UID 0).
May 03 15:08:09 arch-zfs-test systemd[1]: xendriverdomain.service: Main process exited, code=dumped, status=11/SEGV
May 03 15:08:09 arch-zfs-test systemd[1]: xendriverdomain.service: Unit entered failed state.
May 03 15:08:09 arch-zfs-test systemd[1]: xendriverdomain.service: Failed with result 'core-dump'.
May 03 15:08:09 arch-zfs-test systemd-coredump[1742]: Process 1400 (xl) of user 0 dumped core.

                                                      Stack trace of thread 1400:
                                                      #0  0x00007f00df92b19d search_for_guest (libxenlight.so.4.8)
                                                      #1  0x00007f00df92b931 backend_watch_callback (libxenlight.so.4.8)
                                                      #2  0x00007f00df9689da watchfd_callback (libxenlight.so.4.8)
                                                      #3  0x00007f00df96a612 fd_occurs (libxenlight.so.4.8)
                                                      #4  0x00007f00df96a6c4 afterpoll_internal (libxenlight.so.4.8)
                                                      #5  0x00007f00df96bdfd eventloop_iteration (libxenlight.so.4.8)
                                                      #6  0x00007f00df96cbb1 libxl__ao_inprogress (libxenlight.so.4.8)
                                                      #7  0x00007f00df92c1dc libxl_device_events_handler (libxenlight.so.4.8)
                                                      #8  0x0000000000423258 main_devd (xl)
                                                      #9  0x0000000000408e05 main (xl)
                                                      #10 0x00007f00def4f511 __libc_start_main (libc.so.6)
                                                      #11 0x000000000040800a _start (xl)

                                                      Stack trace of thread 1401:
                                                      #0  0x00007f00df2e3f7d read (libpthread.so.0)
                                                      #1  0x00007f00de6bbc3d read_all (libxenstore.so.3.0)
                                                      #2  0x00007f00de6bd6ca read_message (libxenstore.so.3.0)
                                                      #3  0x00007f00de6bda1f read_thread (libxenstore.so.3.0)
                                                      #4  0x00007f00df2da2e7 start_thread (libpthread.so.0)
                                                      #5  0x00007f00df01b54f __clone (libc.so.6)