[Lguest] Passing pointers to/from hypercalls.

[Eric Van Hensbergen]

On Sun, Mar 16, 2008 at 9:07 PM, Rusty Russell <rusty at rustcorp.com.au> wrote:
>  >
>  > Basically, if the guest passes a file name/path to the host, the host
>  > should be able to perform
>  > read/write operations on it, or perform calculations such as check sum on
>  > the file.
>  > (which is within the guest's disk image file)
>  >
>  > Could you please throw some light on it?
>
>  The normal solution is to loopback mount the guest disk file before loading
>  the guest.  I believe there have also been experiments with allowing the
>  guest to access normal host files using 9p, but I don't know any details.
>

We have lguest guests functioning as 9P clients,  If I understand you
correctly, what you are looking for was a 9P server on the guest to
get access to the file system on the underlying disk image.  I may
actually be doing something similar for IBM's Full System Simulator,
but we need to get the in-kernel server merged first (a work in
progress at this point).  Loopback works okay, but can get sticky if
you are dealing with COW images and what not (like we are in
systemsim).  In principal this could be done today over the virtual
network (using 9P, NFS, or other transprots), but we haven't got a
virtio-native channel that a server could use at this point in time.

           -eric