[Xen-API] look into VHD VDI from Control Domain in XCP 1.6

[Alexandre Kouznetsov <alk@xxxxxxxxxx>]

Hello.

I'm trying to mount VM's disk within Control Domain, as part of my 
pre-production tests. My XCP 1.6 installation uses a LVM based local 
storage after a default install. The VM's disks are in VHD format.
In my previous Xen experience, with "raw" volumes as virtual hard disks, 
I have successfully used kpartx, with images stored in files and LVM. 
Clearly, kpartx can't map partitions of a VHD volume.
Within the XCP installation I have found vhdpartx utility, judging by 
it's name and --help output I expected it to be just the tool I need. 
But it's seems there is some problem if I try to use it as kpartx:
[root@xcp47 ~]# lvscan
  ACTIVE 
'/dev/VG_XenStorage-cfc7419f-8b4e-8c51-d619-dfdee09841a2/MGT' [4.00 MB] 
inherit
  ACTIVE 
'/dev/VG_XenStorage-cfc7419f-8b4e-8c51-d619-dfdee09841a2/VHD-bbdf149e-4b41-4a6a-9059-9251365a0a86' 
[8.02 GB] inherit
  ACTIVE 
'/dev/VG_XenStorage-cfc7419f-8b4e-8c51-d619-dfdee09841a2/VHD-fd118da1-c3dd-466b-8b27-32c5db1fcce7' 
[3.01 GB] inherit
[root@xcp47 ~]# vhdpartx -a 
/dev/VG_XenStorage-cfc7419f-8b4e-8c51-d619-dfdee09841a2/VHD-fd118da1-c3dd-466b-8b27-32c5db1fcce7
can't find vhd or lib
[root@xcp47 ~]#

Unfortunately, there is no online man page available in my XCP 
installation, and blktap2 documentation mostly covers Xen's config file 
syntax to to use with VHD storage.
The idea to treat the VHD as a black box is not appealing at all. Is 
there a regular way to access VHD from Dom0? What's wrong with my 
vhdpartx, maybe it is supposed to work in a different way?

I have done my search for alternatives and the most promising reference 
I've found was one that suggests attaching the VDI (or it's snapshot) to 
the Dom0 via a manually created VBD, just as if it was a regular VM.
http://forums.citrix.com/thread.jspa?threadID=252142
It's quite old, and I did not get that solution work ether: I can do all 
the steps, but the disk never showed up within Dom0, even after I 
"vbd-plug" it.

Thank you.

--
Alexandre Kouznetsov


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