Modifying config file during live VM migration

[Kaushik Bhandankar <kaushikb@cc.gatech.edu>]

Hello

I am trying to establish a 9P communication channel between hypervisors 
(vmm) such that when a guest VM sitting on VMM 1 gets live-migrated to 
VMM2, it can still access the VMM1's local disk using the 9P channel 
between VMM 1 and VMM 2.

For the time being, I am looking at changing the configuration file for 
the guest VM.

Initially, when the guest VM is sitting on VMM 1, its IDE disk is 
specified as

disk = [ 'file:/tmp/hd.img,ioemu:hda,w' ]

upon live-migration from VMM1 to VMM2, I would instead want the ide disk 
  to be specified instead as

disk = [ 'remote:/tmp/hd.img,ioemu:hda,w' ]

So that when the IDE disk controller gets a read/write request, it knows 
that the IDE disk is remotely located and hence can send these requests 
to VMM1 using the 9P channel (Rest of the config file stays the same).

Can somebody tell me how the config file of guest VM can be changed 
during "live" VM migration process and where exactly (the code path) 
will this config file will be parsed on VMM2?

Initial look seems to tell me that 
tools/python/xen/xend/XenDomainInfo.py:create() seems to handle the 
creation of domains whereas 
tools/ioemu/xenstore.c:xenstore_parse_domain_config() seems to be 
parsing the domain config file but I am not really sure about where all 
the 'parameters' of a config file get stored and how they are passed to 
the target VMM during live VM migration.

-Kaushik
-- 
"question = ( to ) ? be : ! be;"
                 -- Wm. Shakespeare