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From Donal Lafferty <>
Subject [Proposal] Configuration of Hyper-V SystemVMs
Date Wed, 10 Jul 2013 14:34:38 GMT
Could I get some comments on the following proposal?

System VMs are passed their configuration details in the 'bootArgs' field of the StartCommand
used to create and start them.  For instance, with XenServer, the vm.set_PV_args command is
When the SystemVM is launched, the cloud-early-config script reads this information and sets
up the system VM accordingly.

The current SystemVM does not process its configuration when running on a Hyper-V hypervisor.

Proposed solution:
Pass the data in the KVP service.  KVP is short for key value pair.  This service allows key
/ value strings to be passed between host and guest VM in either direction.
Drivers for Hyper-V's KVP exist in the Debian distro used by the current SystemVM (Debian
Wheezy).  In addition, a user mode daemon, hv_kvp_daemon, must running on the SystemVM.  This
daemon writes the key / value pairs to a file.

-KVP will not work until the O/S is running, which will delay the completion of the StartCommand.
-A binary of hv_kvp_daemon needs to be found.  One option is to build from source, as hv_kvp_daemon
is in the Linux kernel repo.
-If the Hyper-V host does not get proper feedback about whether hv_kvp_daemon wrote a KVP
to file, it will be difficult to tell if the data was passed properly.
-An alternative to the KVP service is to place bootargs in a file on a new volume and attach
this to the system VM.  However, this broadens bootargs functionality to include volume management.

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