Re: [Xen-devel] accessing xen headers from dom0 kernel module

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2010-12-20 at 17:23 +0000, david wrote:
> hi there,
> 
> I'm not very familiar with programming kernel modules, so I have a short 
> question about it.
> Is it possible to use functions defined the in xen/include/ header files 
> of the xen hypervisor in a dom0 kernel-module?
> I think my dom0 kernel does not export the required symbols to use this 
> functions, so it will not work, right?

The interfaces defined in xen/include are internal to the hypervisor and
are not available to guests. In particular a guest can never call a
hypervisor symbol directly as you seem to be asking.

The exception to this is xen/include/public which contains the guest
(including dom0) hypercall interface (and some other shared-memory data
structures). A hypercall is a trap somewhat analogous to a system call
except it is from guest->hypervisor rather than userspace->kernel. They
are invoked by calling into an offset within the hypercall page (a
special page populated with the correct trap instruction for the
architecture).

Most (all?) guests do not build directly against the headers in the Xen
source tree but instead import a copy into their own source, adjusting
for local coding style etc. In Linux these interface headers are in
include/xen/interface. Linux also defines it's own higher level
interfaces to hypercalls (convenience functions and the like), these are
generally in include/xen or arch/x86/include/asm/xen.

Ian.


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