Re: accessing xen headers from dom0 kernel module

[david <david_n@gmx.at>]

On 12/21/2010 11:02 AM, Ian Campbell wrote:
> 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.
>
>

That's exactly what I wanted to know. Thanks for your fast response.

david