Xen devel - Oct 2007 - Modifying config file during live VM migration

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

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On 10/27/07, Kaushik Bhandankar <kaushikb@cc.gatech.edu>
wrote:
> 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'' ]
>
I would suggest that you''d be better off letting some form of dynamic
name space take care of this for you.  That is to say, establish a
canonical location for resources your partition needs and make sure
those resources (whether local or remote) are always bound there.  The
necessary (first?) step during migration would be to establish the
correct mounts (or binds) of those resources to the canonical
location.  You might even be able to use a synthetic file system to
help provide these resources based on some standardize URI naming
scheme.

               -eric

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