[Xen-devel] [PATCH] External device migration support

[Stefan Berger <stefanb@xxxxxxxxxx>]

This patch enables external devices, such as for example a mounted hard
drive image or a TPM, to be migrated to a remote machine. The patch
hooks into the checkpointing (XendCheckpoint.py) code and performs
migration in 4 different steps:

In a 1st step (step = 0 in the code) migration of all devices of a
domain is 'tested', that means their driver implementations (blkif.py,
netif.py, tpmif.py, usbif.py, pciif.py) are queried whether migration is
possible at all. Currently all device representations respond with a
'yes' (=0), although probably a VM mounting a hard drive partition
should respond with a 'no' (-1) already. This first step is a quick
check to see whether devices can be migrated.

The 2nd step is to do whatever can be done before the domain is
suspended. At this point migration of the device could be initiated, if
at all possible.

The 3rd step is to migrate a device after the domain has been suspended,
meaning that it is not scheduled anymore and the VM is 'settled'. All
devices are called again and a good implementation would initiate the
migration in a background process to achieve as much concurrency as
possible.

The 4th step is to synchronize with the 3rd step. At this point the
implementor has to make sure that anything that was initiated in step 3
has completed. Once all steps 4 have been processed, the VM will resume
on the remove machine.

I have implemented hooks for migration of a TPM. These hooks for now
call the os.system() call with a configurable tool but a fixed parameter
set and refuse to migrate a VM attached to a virtual TPM if no tool has
been provided for migration.
All other devices do not currently overload the 'migrate' method defined
in the DevController.py and therefor will just let migration happen.

Please let me know what you think about this idea.

Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxx>

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