[Xen-users] xen_blkbk times out before getting connected

[Yathindra <ydev@xxxxxxxxxxx>]

Hi,

When ever I start a guest domain, backend driver times out since state 
is not being connected. How do we debug such issues ?
I instrumented the backend drivers, specifically 
xen/xenbus/xenbus_probe.c and xen/xenbus/xenbus_probe_backend.c to see
if the backend fails to probe the device. But I never saw any of the 
messages I added in syslog or dmesg. I'm stuck on this problem
for weeks now. I'm not understanding why the backend fails to switch the 
state.
Heres the libxl log:

libxl: debug: libxl_device.c:313:libxl__device_disk_set_backend: Disk 
vdev=sda1 spec.backend=unknown
libxl: debug: libxl_device.c:349:libxl__device_disk_set_backend: Disk 
vdev=sda1, using backend phy
libxl: debug: libxl_create.c:821:initiate_domain_create: running bootloader
libxl: debug: libxl_bootloader.c:327:libxl__bootloader_run: no 
bootloader configured, using user supplied kernel
libxl: debug: libxl_event.c:561:libxl__ev_xswatch_deregister: watch 
w=0xc3a5e0: deregister unregistered
libxl: debug: libxl_numa.c:435:libxl__get_numa_candidate: New best NUMA 
placement candidate found: nr_nodes=1, nr_cpus=2, nr_vcpus=3, free_memkb=997
libxl: detail: libxl_dom.c:192:numa_place_domain: NUMA placement 
candidate with 1 nodes, 2 cpus and 997 KB free selected
domainbuilder: detail: xc_dom_allocate: 
cmdline="root=/dev/disk/by-path/xen-vbd-2049 ro xencons=tty", 
features="(null)"
libxl: debug: libxl_dom.c:393:libxl__build_pv: pv kernel mapped 0 path 
/boot/vmlinuz-3.2.16
...
...
libxl: debug: libxl_event.c:512:libxl__ev_xswatch_register: watch 
w=0xc3bd98 wpath=/local/domain/0/backend/vbd/1/2049/state token=3/0: 
register slotnum=3
libxl: debug: libxl_create.c:1330:do_domain_create: ao 0xc39880: 
inprogress: poller=0xc398e0, flags=i
libxl: debug: libxl_event.c:457:watchfd_callback: watch w=0xc3bd98 
wpath=/local/domain/0/backend/vbd/1/2049/state token=3/0: event 
epath=/local/domain/0/backend/vbd/1/2049/state
libxl: debug: libxl_event.c:600:devstate_watch_callback: backend 
/local/domain/0/backend/vbd/1/2049/state wanted state 2 still waiting 
state 1
libxl: debug: libxl_event.c:614:devstate_timeout: backend 
/local/domain/0/backend/vbd/1/2049/state wanted state 2  timed out
libxl: debug: libxl_event.c:549:libxl__ev_xswatch_deregister: watch 
w=0xc3bd98 wpath=/local/domain/0/backend/vbd/1/2049/state token=3/0: 
deregister slotnum=3
libxl: debug: libxl_event.c:561:libxl__ev_xswatch_deregister: watch 
w=0xc3bd98: deregister unregistered
libxl: error: libxl_device.c:943:device_backend_callback: unable to 
connect device with path /local/domain/0/backend/vbd/1/2049
libxl: error: libxl_create.c:1077:domcreate_launch_dm: unable to add 
disk devices
libxl: debug: libxl_event.c:512:libxl__ev_xswatch_register: watch 
w=0xc3d868 wpath=/local/domain/0/backend/vbd/1/2049/state token=3/1: 
register slotnum=3
libxl: debug: libxl_event.c:457:watchfd_callback: watch w=0xc3d868 
wpath=/local/domain/0/backend/vbd/1/2049/state token=3/1: event 
epath=/local/domain/0/backend/vbd/1/2049/state
libxl: debug: libxl_event.c:600:devstate_watch_callback: backend 
/local/domain/0/backend/vbd/1/2049/state wanted state 6 still waiting 
state 5
libxl: debug: libxl_event.c:614:devstate_timeout: backend 
/local/domain/0/backend/vbd/1/2049/state wanted state 6  timed out
libxl: debug: libxl_event.c:549:libxl__ev_xswatch_deregister: watch 
w=0xc3d868 wpath=/local/domain/0/backend/vbd/1/2049/state token=3/1: 
deregister slotnum=3
libxl: debug: libxl_event.c:561:libxl__ev_xswatch_deregister: watch 
w=0xc3d868: deregister unregistered
libxl: error: libxl_device.c:943:device_backend_callback: unable to 
disconnect device with path /local/domain/0/backend/vbd/1/2049
libxl: error: libxl.c:1725:devices_destroy_cb: libxl__devices_destroy 
failed for 1
libxl: debug: libxl_event.c:1497:libxl__ao_complete: ao 0xc39880: 
complete, rc=-3
libxl: debug: libxl_event.c:1469:libxl__ao__destroy: ao 0xc39880: destroy
xc: debug: hypercall buffer: total allocations:366 total releases:366
xc: debug: hypercall buffer: current allocations:0 maximum allocations:4
xc: debug: hypercall buffer: cache current size:4
xc: debug: hypercall buffer: cache hits:356 misses:4 toobig:6

Thanks,
Yathi

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