Re: [Xen-devel] sharing file between running domU (windowxp) and dom0

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> As far as i know, both domU and dom0 runs in isolation. I want to modify a
> particular file of running domU(xp) from dom0.
>
> i have tried to pause the domu, then using lomount, mount its image and
> then modifying the file and umounting the image. But when i unpause domu,
> it does not reflect the changes.

You should never, ever do that.  You *must always* shut down a domain before 
modifying its filesystem from the outside.  Otherwise you can create 
corruption that will destroy the domain's disk data.  Just pausing the domain 
or saving it is not enough to protect you, and neither will using the 
guest's "hibernate" feature.  The domain *really* has to be properly shut 
down.

I'm sorry to emphasize that so harshly but it really is very very important.

This is because filesystems are written with the assumption that they "own" 
the disk and that nothing will ever change "underneath" them.  If you modify 
the filesystem from the outside then you're doing stuff without the guest OS 
knowing about it.  It won't be looking for this and will get confused.  This 
could seriously damage your filesystem.

If you do it by accident, you could try xm destroy-ing the domain immediately 
in order to prevent it getting confused by the changes to the underlying 
disk - before it has time to corrupt anything.  xm destroying a domain which 
is modifying the filesystem has corruption risks of its own though (and will 
lose any in-memory data), so it's better just to avoid this situation.

I hope that helps.  Again, sorry to be so harsh, but this is one thing about 
virtual machines that is *really* important to watch out for, or you will 
have major problems at some stage.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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