Re: [Xen-devel] Another migration question

["M.A. Williamson" <maw48@xxxxxxxxx>]

>   I had a look at the migration code in the kernel 
> (arch/xen/kernel/reboot:__do_suspend()). I am surprised that migration 
> actually seems possible when the block device frontend has mounted a 
> device. Shouldn't it rather refuse to be suspended, assuming that the 
> partition can be migrated to another machine and possibly harm a 
> filesystem there? I would also think that there should be a user-level 
> daemon trying to unmount hard drive partitons before any migration is 
> initited. I suppose the same problem will arise with the USB driver.
The idea is that the block device should be available at the destination 
(e.g. by using some network storage system, SAN or other mechanism). The 
device channel can then just reconnect and carry on.
USB is a little trickier because there isn't a straightforward way to 
ensure the guest can still access the device after the migration nor to 
make the process transparent to the guest USB stack. For this reason, USB 
doesn't support suspend, so you can't suspend a USB frontend domain. We can 
probably do a bit better e.g. fake out port disconnects on suspend then 
allow a device reconnect on resume - it won't be transparent but it'll be 
more useful.
Cheers,
Mark


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