[PATCH 1/2] tools/hotplug: fix invalid frontend path for set_mtu

[James Dingwall <james-xen@xxxxxxxxxxxxxx>]

From: James Dingwall <james@xxxxxxxxxxxxxx>

The set_mtu() function of xen-network-common.sh currently has this code:

        if [ ${type_if} = vif ]
        then
            local dev_=${dev#vif}
            local domid=${dev_%.*}
            local devid=${dev_#*.}

            local FRONTEND_PATH="/local/domain/$domid/device/vif/$devid"

            xenstore_write "$FRONTEND_PATH/mtu" ${mtu}
        fi

This works fine if the device has its default name but if the xen config
defines the vifname parameter the FRONTEND_PATH is incorrectly constructed.
Learn the frontend path by reading the appropriate value from the backend.

Also change use of `...` to $(...) for a consistent style in the script.

Signed-off-by: James Dingwall <james@xxxxxxxxxxxxxx>
---
 tools/hotplug/Linux/xen-network-common.sh | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/tools/hotplug/Linux/xen-network-common.sh 
b/tools/hotplug/Linux/xen-network-common.sh
index 0150a4840e..f83eeef030 100644
--- a/tools/hotplug/Linux/xen-network-common.sh
+++ b/tools/hotplug/Linux/xen-network-common.sh
@@ -161,7 +161,7 @@ set_mtu () {
     local mtu=$(xenstore_read_default "$XENBUS_PATH/mtu" "")
     if [ -z "$mtu" ]
     then
-        mtu="`ip link show dev ${bridge}| awk '/mtu/ { print $5 }'`"
+        mtu="$(ip link show dev ${bridge}| awk '/mtu/ { print $5 }')"
         if [ -n "$mtu" ]
         then
             log debug "$bridge MTU is $mtu"
@@ -174,11 +174,7 @@ set_mtu () {
 
         if [ ${type_if} = vif ]
         then
-            local dev_=${dev#vif}
-            local domid=${dev_%.*}
-            local devid=${dev_#*.}
-
-            local FRONTEND_PATH="/local/domain/$domid/device/vif/$devid"
+            local FRONTEND_PATH="$(xenstore_read "$XENBUS_PATH/frontend")"
 
             xenstore_write "$FRONTEND_PATH/mtu" ${mtu}
         fi
-- 
2.55.0