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Re: adding /dev/xen/gnttab

> On Thu, Sep 02, 2010 at 04:00:44PM +0200, Christoph Egger wrote:
> > 
> > Hi!
> > 
> > For gnttab support a new device file is needed for a new set
> > of ioctl()'s.
> Can you explain what feature needs this gnttab device ?

Look at xentools33/patches/patch-aj

gnttab is needed
a) to make xen tools compile
b) for the grant table hypercalls in
   sys/arch/xen/include/xen3-public/grant_table.h used by
   xen tools
c) for pci passthrough into HVM/PV guests
d) for PV drivers in HVM guests
d) for other things I'm not aware of

grant table is a feature that allows a guest to
give/remove permissions to/from given memory pages
to be accessed by an other guest either read-only
or read-write. The 'other guest' may be the Dom0 or
a backend domain.

BTW: Xen people are about rewriting the python code in C.
'xl' is written in C and will replace 'xm'.
You say, you don't know python and that hold you back from
doing anything there. Now you can join the game and implement
pci passthrough in xl.

> > Attached patch adds /dev/xen/gnttab.
> I see only patch for /dev/MAKEDEV, did you forget to
> attach the diff for this device support ?

I implemented the stubs for NetBSD by adopting the Linux
implementation. No, not for xen 3.3 but for xen-unstable
which is heading to Xen 4.1.

The kernel side is not yet written.
I just want to have the device file as a first step.

> > I would like to use the opportunity to move xen device files
> > into /dev/xen/. The patch keeps the existing ones for backward
> > compatibility.
> Looks good to me.

Thanks. Oh, do you mind if I add privcmd to /dev/xen/ as well?
The kernel code to use /dev/xen/privcmd should be easy to adopt
and will finally allow to remove kernfs.


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