[Xen-users] xm save --checkpoint does not works

[Abhijeet Kumar Sinha <abhijeet.aks@xxxxxxxxx>]

Hello

We are trying to periodically save the running state of domU
instances. We are trying to achieve this with least disruption in the
services running inside the instances. Hence the suspend time should
be minimum.

We are trying to use the command xm save --checkpoint <Domain> <CheckpointFile>

As per help, this says that using the --checkpoint will resume the
instance after the checkpoint is saved, but it is not happening such

We are running a domU with the following cfg file


name = "snapshot-test"
kernel = "/home/abhijeet/boot/vmlinuz-2.6.18-128.el5xen"
ramdisk = "/home/abhijeet/boot/initrd-2.6.18-128.el5xen.img"
disk = [ 'tap:qcow2:/home/abhijeet/qcow2/snapshot-test/qcow2-image.qcow2,xvda,w'
]
root = "/dev/xvda3 ro"
memory=512
vcpus=1
vif = ['']
vfb = [ 'type=vnc,vncdisplay=10' ]

When we issue the following command

xm save --checkpoint snapshot-test qcow2-image.save

the image is saved but the VM does not resumes.

xm list has the following output

xm list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0 23645     8     r-----   1040.8
snapshot-test                                3   512     1     ---s--     27.9

virt-manager shows instance in "Shutoff" state

None of the following commands have any effect

xm unpause
xm resume
xm reset

xm uptime called at regular intervals show that the VM is up as
runtime is shown increasing.

xm start brings the VM in an conflicting state

[root@xen1 raw2qcow2]# xm start snapshot-test
Error: Device 0 (vkbd) is already connected.

After this, in virt-manager VM is shown to be in "shutoff" state, but
under ID the value changes from 3 to nothing, memory usage changes
from 0% to 1% every second.

Following is the 'xm info' output for reference


release                : 2.6.18-164.el5xen
version                : #1 SMP Thu Sep 3 04:03:03 EDT 2009
machine                : x86_64
nr_cpus                : 8
nr_nodes               : 1
cores_per_socket       : 4
threads_per_core       : 1
cpu_mhz                : 3158
hw_caps                :
bfebfbff:20100800:00000000:00000140:000ce3bd:00000000:00000001:00000000
virt_caps              : hvm
total_memory           : 32767
free_memory            : 2
node_to_cpu            : node0:0-7
node_to_memory         : node0:2
xen_major              : 3
xen_minor              : 4
xen_extra              : .0
xen_caps               : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler          : credit
xen_pagesize           : 4096
platform_params        : virt_start=0xffff800000000000
xen_changeset          : unavailable
cc_compiler            : gcc version 4.1.2 20080704 (Red Hat 4.1.2-44)
cc_compile_by          : root
cc_compile_domain      : gitco.tld
cc_compile_date        : Fri May 29 21:39:26 CEST 2009
xend_config_format     : 4

/var/log/xen/xen-hotplug.log has the following lines repeated many a times

xenstore-read: couldn't read path backend/tap/0/51952/params

Dom0 is CentOS 5.3 x86_64

Is this functionality of saving the domU state, while leaving the
instance running broken ?

Any help in this regard will be highly appreciated.

-- 
Regards,
Abhijeet

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