tools: init.d/Linux/xencommons: run script only when needed

Currently xencommons prints an error that /proc/xen/capabilities does
not exist when started on a non-xen kernel.

Update the xencommons script to run only when needed:
- do not run if /proc/xen does not exist
- check if /proc/xen/capabilities exists before doing the grep for dom0

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

xen-unstable changeset: 24333:4002e63b188a
Backport-requested-by: Olaf Hering <olaf@aepfle.de>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/hotplug/Linux/init.d/xencommons

@@ -29,15 +29,24 @@ test -f $xencommons_config/xencommons && . $xencommons_config/xencommons
 XENCONSOLED_PIDFILE=/var/run/xenconsoled.pid
 shopt -s extglob
 
+# not running in Xen dom0 or domU
+if ! test -d /proc/xen ; then
+	exit 0
+fi
+
+# mount xenfs in dom0 or domU with a pv_ops kernel
 if test "x$1" = xstart && \
-     test -d /proc/xen && \
    ! test -f /proc/xen/capabilities && \
    ! grep '^xenfs ' /proc/mounts >/dev/null;
 then
 	mount -t xenfs xenfs /proc/xen
 fi
 
-if ! grep -q "control_d" /proc/xen/capabilities ; then
+# run this script only in dom0:
+# no capabilities file in xenlinux domU kernel
+# empty capabilities file in pv_ops domU kernel
+if test -f /proc/xen/capabilities && \
+   ! grep -q "control_d" /proc/xen/capabilities ; then
 	exit 0
 fi