Re: [Xen-devel] how to see the data changing in a running domain?

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> So clearly everything made changed inside domainU cannot be seen from
> outside (domain0).
> Anybody can please explain to me why, and if 
> possible, how could I watch data of domainU (in realtime) from
> domain0?

The DomU will be caching the updates to its disk in memory before writing them 
to the disk.  Likewise, Dom0 will be caching data it's read and assuming it 
stays the same (most filesystems assume only one writer, so dom0 thinks it 
knows when the disk is modified).

The result of this is that dom0 won't immediately notice the changes domU has 
made.  When it does notice, it'll likely take the form of an error along the 
lines of "Something changed on this filesystem that I wasn't expecting."

As Ian says, the GFS and OCFSv2 filesystems are explicitly aware of concurrent 
access so they'll cope with this OK.

The easiest solution for your purposes would be to use NFS root in the domU 
(with the root FS exported from dom0) or to run an NFS server in the domU and 
export the root FS to dom0.

HTH,
Mark


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