Re: [Xen-devel] [PATCH] qemu-xen: make use of xenstore relative paths

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Sep 26, 2013 at 07:20:31PM +0200, Roger Pau Monné wrote:
> On 26/09/13 18:46, Anthony PERARD wrote:
> > On Wed, Sep 18, 2013 at 09:50:58PM +0200, Roger Pau Monne wrote:
> >> Qemu has several hardcoded xenstore paths that are only valid on Dom0.
> >> Attempts to launch a Qemu instance (to act as a userspace backend for
> >> PV disks) will fail because Qemu is not able to access those paths
> >> when running on a domain different than Dom0.
> >>
> >> Instead make the xenstore paths relative to the domain where Qemu is
> >> actually running.
> >>
> >> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> >> Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> >> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > This look fine. One issue with the patch: the file xen_backend.c have
> > been moved to hw/xen/xen_backend.c.
> 
> Thanks, this is based on the stable Qemu version in Xen tree, I should
> have done the change on top of the main qemu.git repo.
> 
> > I've also tryied it in a stubdomain, and it does not boot anymore
> > because the qemu in the stubdom can not read the state.  I have tried
> > again without the change in xen-all.c, and the stubdom does not complain
> > anymore. So in the change in xenstore_record_dm_state() needed as well?
> 
> Yes, if we run a Qemu instance inside a driver domain it wouldn't make
> much sense IMHO to write the state of that Qemu instance on a xenstore
> path that belongs to the Dom0, and also we would need to give the driver
> domain permissions to write on a xenstore path that's inside the Dom0
> xenstore path, which doesn't seem like a good idea.
> 
> To make Qemu work on a domain different than Dom0 you will also need the
> following patch from my driver domain series:
> 
> http://marc.info/?l=xen-devel&m=137993233817018
> 
> If not the guest is unable to create the device-model/<domid>/state
> xenstore entry. For stubdomains would it be really hard to change the
> Dom0 to check for /local/domain/<stubdom_id>/device-model/<domid>/state
> instead of /local/domain/0/device-model/<domid>/state?

I have tried with the patch applied to libxl, and stubdom work fine with
the changes to the xenstore paths. So, once the xen_backend.c file is in
the new path, you can add my:
Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

-- 
Anthony PERARD

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