remus: init sch_plug module based on kernel version

remus: init sch_plug module based on kernel version

sch_plug module, for network buffering, is available as part of linux
kernel (from 3.4 onwards), as opposed to an out-of-tree module.
The netlink message format to talk to the in-kernel module is different from
that of the old version.  So, before initializing the Plug Qdisc, check
the kernel version and use the appropriate message format.

Also change the names of the constants to reflect the format used by the mainline
module [CHECKPOINT -> BUFFER , RELEASE -> RELEASE_ONE ].

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>

tools/python/xen/remus/device.py

@@ -332,12 +332,12 @@ class BufferedNIC(CheckpointedDevice):
         if not self.installed:
             self.install()
 
-        self._sendqmsg(qdisc.TC_PLUG_CHECKPOINT)
+        self._sendqmsg(qdisc.TC_PLUG_BUFFER)
 
     def commit(self):
         '''Called when checkpoint has been acknowledged by
         the backup'''
-        self._sendqmsg(qdisc.TC_PLUG_RELEASE)
+        self._sendqmsg(qdisc.TC_PLUG_RELEASE_ONE)
 
     # private
     def _sendqmsg(self, action):

tools/python/xen/remus/qdisc.py

@@ -1,6 +1,9 @@
 import socket, struct
 
 import netlink
+import platform
+
+kernelversion = platform.platform(terse=True).split("-")[1].split(".")
 
 qdisc_kinds = {}
 
@@ -146,13 +149,18 @@ class CfifoQdisc(Qdisc):
 
 qdisc_kinds['cfifo'] = CfifoQdisc
 
-TC_PLUG_CHECKPOINT = 0
-TC_PLUG_RELEASE = 1
+TC_PLUG_BUFFER = 0
+TC_PLUG_RELEASE_ONE = 1
 
 class PlugQdisc(Qdisc):
-    fmt = 'I'
 
     def __init__(self, qdict=None):
+        if int(kernelversion[0]) >= 3 and int(kernelversion[1]) >= 4:
+            self.fmt = 'iI'
+            self.limit = 10000
+        else:
+            self.fmt = 'I'
+
         if not qdict:
             qdict = {'kind': 'plug',
                      'handle': TC_H_ROOT}
@@ -161,7 +169,10 @@ class PlugQdisc(Qdisc):
         self.action = 0
 
     def pack(self):
-        return struct.pack(self.fmt, self.action)
+        if int(kernelversion[0]) >= 3 and int(kernelversion[1]) >= 4:
+            return struct.pack(self.fmt, self.action, self.limit)
+        else:
+            return struct.pack(self.fmt, self.action)
 
     def parse(self, args):
         if not args:
@@ -169,9 +180,9 @@ class PlugQdisc(Qdisc):
         arg = args[0]
 
         if arg == 'checkpoint':
-            self.action = TC_PLUG_CHECKPOINT
+            self.action = TC_PLUG_BUFFER
         elif arg == 'release':
-            self.action = TC_PLUG_RELEASE
+            self.action = TC_PLUG_RELEASE_ONE
         else:
             raise QdiscException('unknown action')