[Please remember to post all questions on the mailing list]

On Thu, Mar 08, 2012 at 09:41:19PM +0700, Tho Huynh wrote:
> Can I mount the guest's file system into a folder/path (mountpoint)
> in the host machine using guestfish?

No, but you don't need to.

> And accessing that folder equal to accessing the guest's file
> system.  What I'm trying to do is to copy a file from one guest to
> another directly but to achieve full disk speed.

Guestfish cannot connect to two guests at the same time, so you would
need to download the file from one guest and upload it to the other.
(I'm still assuming here that you are using libguestfs live).  eg:

  guestfish --live -d Source download /some/file /tmp/file
  guestfish --live -d Destination upload /tmp/file /some/file

If that isn't fast enough or you need to avoid the local copy, it is
possible to connect two handles together and copy the file directly
between them, but you'd have to write a script against the API (eg. in
Perl/Python/etc).

    .  .  .

In the *non-live* case, there is another method: add the disks of both
guests, 'launch', and copy the file between mountpoints (see the
'mkmountpoint' command).  Surprisingly, this is not necessarily going
to be faster than downloading and uploading.  This method also has
some limitations -- it's not possible to use two guests that have
conflicting volume group names; and even security issues -- a
malicious guest could interfere with the other guest.

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://et.redhat.com/~rjones/virt-df/