[xen master] tools/hotplug/Linux: modify set_mtu() to optionally use a configured value...

[patchbot@xxxxxxx]

commit c7c6de0cb9b00efc203790743ef8c37ba113d3ee
Author:     Paul Durrant <pdurrant@xxxxxxxxxx>
AuthorDate: Tue Aug 11 09:02:00 2020 +0100
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Thu Aug 27 10:04:21 2020 +0000

    tools/hotplug/Linux: modify set_mtu() to optionally use a configured 
value...
    
    ...and also inform the frontend.
    
    The set_mtu() function in xen-network-common.sh currently sets the backend
    vif MTU to match that of the bridge.
    
    A prior patch added code into libxl such that a tools-configured 'mtu' value
    may be present in the xenstore backend area. If the node is present in
    xenstore then it should be authoritative. Hence set_mtu() is modified to 
only
    read the MTU of the bridge if it is not present.
    
    The function is also modified to write whatever value it applies to the
    backend vif into the xenstore frontend area where is may then be used to
    configure the frontend network stack.
    
    NOTE: There is also a small modification replacing '$mtu' with '${mtu}'
          for style consistency.
    
    Signed-off-by: Paul Durrant <pdurrant@xxxxxxxxxx>
    Acked-by: Wei Liu <wl@xxxxxxx>
---
 tools/hotplug/Linux/vif-bridge            |  2 +-
 tools/hotplug/Linux/xen-network-common.sh | 28 ++++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/tools/hotplug/Linux/vif-bridge b/tools/hotplug/Linux/vif-bridge
index e1d7c49788..b99cc82a21 100644
--- a/tools/hotplug/Linux/vif-bridge
+++ b/tools/hotplug/Linux/vif-bridge
@@ -81,7 +81,7 @@ case "$command" in
         ;&
     online)
         setup_virtual_bridge_port "$dev"
-        set_mtu "$bridge" "$dev"
+        set_mtu "$bridge" "$dev" "$type_if"
         add_to_bridge "$bridge" "$dev"
         ;;
     remove)
diff --git a/tools/hotplug/Linux/xen-network-common.sh 
b/tools/hotplug/Linux/xen-network-common.sh
index 6a0904361f..82ee70aab4 100644
--- a/tools/hotplug/Linux/xen-network-common.sh
+++ b/tools/hotplug/Linux/xen-network-common.sh
@@ -164,9 +164,33 @@ remove_from_bridge () {
 set_mtu () {
     local bridge=$1
     local dev=$2
-    mtu="`ip link show dev ${bridge}| awk '/mtu/ { print $5 }'`"
+    local type_if=$3
+
+    XENBUS_PATH="${XENBUS_PATH:?}"
+
+    local mtu=$(xenstore_read_default "$XENBUS_PATH/mtu" "")
+    if [ -z "$mtu" ]
+    then
+        mtu="`ip link show dev ${bridge}| awk '/mtu/ { print $5 }'`"
+        if [ -n "$mtu" ]
+        then
+            log debug "$bridge MTU is $mtu"
+        fi
+    fi
     if [ -n "$mtu" ] && [ "$mtu" -gt 0 ]
     then
-            ip link set dev ${dev} mtu $mtu || :
+        log debug "setting $dev MTU to $mtu"
+        ip link set dev ${dev} mtu ${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"
+
+            xenstore_write "$FRONTEND_PATH/mtu" ${mtu}
+        fi
     fi
 }
--
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