RE: [Xen-devel] Another migration question

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

>   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? 

We could build in more idiot proofing into xend, but the current
situation works fine for someone that knows what they're doing. 

For migration to work it obviously has to be possible to access the old
block device in the new place. You can do this with a SAN, iSCSI, GNBD,
drdb etc.

> 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.

It's not possible to unmount your root filesystem. I guess we could put
a few sanity checks in to ensure that the contents of the device after
the migrate appears to be the same as before, but this is non-trivial
and could potetnailly trigger false positives e.g. in the case of GFS or
OCFS2.

The next generation tools might provide more saftey checks to help stop
people shooting their own feet...

Ian




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