[BUG] libxl: error: libxl_device.c:301:libxl__device_disk_set_backend: no suitable backend for disk

["Alex Braunegg" <alex.braunegg@gmail.com>]

Hi all,

I have been testing the Xen 4.6.0 packages - however I have found the
following issue with attempting to perform the following commands:

	[root@mynas-s5000xvn ~]# xl cd-eject test2 hdc         
	libxl: error: libxl_device.c:301:libxl__device_disk_set_backend: no
suitable backend for disk hdc
	[root@mynas-s5000xvn ~]#

Verbose logging of the issue presents the following:

----------------------------------------------------

libxl: debug: libxl.c:2841:libxl_cdrom_insert: ao 0xe68c30: create:
how=(nil) callback=(nil) poller=0xe68cc0
libxl: debug: libxl_device.c:269:libxl__device_disk_set_backend: Disk
vdev=hdc spec.backend=unknown
libxl: debug: libxl_device.c:215:disk_try_backend: Disk vdev=hdc, backend
phy unsuitable as phys path not a block device
libxl: debug: libxl_device.c:298:libxl__device_disk_set_backend: Disk
vdev=hdc, using backend qdisk
libxl: debug: libxl_device.c:269:libxl__device_disk_set_backend: Disk
vdev=hdc spec.backend=phy
libxl: debug: libxl_device.c:215:disk_try_backend: Disk vdev=hdc, backend
phy unsuitable as phys path not a block device
libxl: error: libxl_device.c:301:libxl__device_disk_set_backend: no suitable
backend for disk hdc
libxl: debug: libxl_event.c:1853:libxl__ao_create_fail: ao 0xe68c30: create
fail
libxl: debug: libxl_event.c:1843:libxl__ao__destroy: ao 0xe68c30: destroy
xc: debug: hypercall buffer: total allocations:20 total releases:20
xc: debug: hypercall buffer: current allocations:0 maximum allocations:2
xc: debug: hypercall buffer: cache current size:2
xc: debug: hypercall buffer: cache hits:12 misses:2 toobig:6

----------------------------------------------------

There was a thread on this in 2013
(http://lists.xen.org/archives/html/xen-devel/2013-03/msg00806.html) however
I have looked at the disk configuration, and there is no phy: / raw: / file:
prefix to the disk specification.

The VM configuration is as follows:

----------------------------------------------------

builder='hvm'
memory = 512
shadow_memory = 8
uuid = '4789b84d-3cdd-409f-9899-88bb13652176'
name = 'test2'
vif = [ 'bridge=br0, mac=00:16:3e:f1:48:8c' ]
disk = [
'/dev/zvol/storage0/xen/test2/disk_sda,,hda','/storage0/data-shares/iso/Cent
OS-6.5-x86_64-minimal.iso,,hdc,cdrom' ]
boot='dc'
sdl=0
vnc=1
vncconsole=1
vnclisten='0.0.0.0'
stdvga=1
serial='pty'
usbdevice='tablet'
vncpasswd='asdf1234'
vncdisplay=0
localtime=1
audio='1'
soundhw='ac97'

----------------------------------------------------

Additionally, if I attempt to insert the ISO file (which I expect it to fail
as I have not ejected it yet), I get some additional information which may
be beneficial in diagnosing the eject issue:

----------------------------------------------------
[root@mynas-s5000xvn ~]# xl -vvvv cd-insert test2 hdc
/storage0/data-shares/iso/CentOS-6.5-x86_64-minimal.iso
libxl: debug: libxl.c:2841:libxl_cdrom_insert: ao 0x101cc30: create:
how=(nil) callback=(nil) poller=0x101ccc0
libxl: debug: libxl_device.c:269:libxl__device_disk_set_backend: Disk
vdev=hdc spec.backend=unknown
libxl: debug: libxl_device.c:215:disk_try_backend: Disk vdev=hdc, backend
phy unsuitable as phys path not a block device
libxl: debug: libxl_device.c:298:libxl__device_disk_set_backend: Disk
vdev=hdc, using backend qdisk
libxl: debug: libxl_device.c:269:libxl__device_disk_set_backend: Disk
vdev=hdc spec.backend=phy
libxl: debug: libxl_qmp.c:706:libxl__qmp_initialize: connected to
/var/run/xen/qmp-libxl-37
libxl: debug: libxl_qmp.c:296:qmp_handle_response: message type: qmp
libxl: debug: libxl_qmp.c:555:qmp_send_prepare: next qmp command: '{
    "execute": "qmp_capabilities",
    "id": 1
}
'
libxl: debug: libxl_qmp.c:296:qmp_handle_response: message type: return
libxl: debug: libxl_qmp.c:555:qmp_send_prepare: next qmp command: '{
    "execute": "eject",
    "id": 2,
    "arguments": {
        "device": "ide-5632"
    }
}
'
libxl: debug: libxl_qmp.c:296:qmp_handle_response: message type: error
libxl: error: libxl_qmp.c:287:qmp_handle_error_response: received an error
message from QMP server: Device 'ide-5632' is locked
libxl: debug: libxl_event.c:1853:libxl__ao_create_fail: ao 0x101cc30: create
fail
libxl: debug: libxl_event.c:1843:libxl__ao__destroy: ao 0x101cc30: destroy
xc: debug: hypercall buffer: total allocations:26 total releases:26
xc: debug: hypercall buffer: current allocations:0 maximum allocations:2
xc: debug: hypercall buffer: cache current size:2
xc: debug: hypercall buffer: cache hits:17 misses:2 toobig:7
[root@mynas-s5000xvn ~]#
----------------------------------------------------


Any suggestions is greatly appreciated.


Best regards,

Alex