tools: use sysfs interface to balloon driver if present

The pvops dom0 kernel does not expose the balloon driver via /proc/xen, so use the sysfs interface.

diff -r 1944c39d0007 tools/python/xen/xend/osdep.py
@@ -38,7 +38,10 @@
    "SunOS": "vif-vnic"

}

-def _linux_balloon_stat(label):
+PROC_XEN_BALLOON = '/proc/xen/balloon'
+SYSFS_XEN_MEMORY = '/sys/devices/system/xen_memory/xen_memory0' +
+def _linux_balloon_stat_proc(label):
"""Returns the value for the named label, or None if an error occurs."""

xend2linux_labels = { 'current' : 'Current allocation',
@@ -47,7 +50,6 @@
'high-balloon' : 'High-mem balloon',
'limit' : 'Xen hard limit' }

- PROC_XEN_BALLOON = '/proc/xen/balloon'
f = file(PROC_XEN_BALLOON, 'r')
try:
for line in f:
@@ -61,6 +63,29 @@

        return None
    finally:
        f.close()
+
+def _linux_balloon_stat_sysfs(label):
+    sysfiles = { 'target'       : 'target_kb',
+                 'current'      : 'info/current_kb',
+                 'low-balloon'  : 'info/low_kb',

+ 'high-balloon' : 'info/high_kb',
+ 'limit' : 'info/hard_limit_kb' }
+
+ name = os.path.join(SYSFS_XEN_MEMORY, sysfiles[label])
+ f = file(name, 'r')
+
+ val = f.read().strip()
+ if val.isdigit():
+ return int(val)
+ return None
+
+def _linux_balloon_stat(label):
+ if os.access(PROC_XEN_BALLOON, os.F_OK):
+ return _linux_balloon_stat_proc(label)
+ elif os.access(SYSFS_XEN_MEMORY, os.F_OK):
+ return _linux_balloon_stat_sysfs(label)
+
+ return None

def _solaris_balloon_stat(label):
"""Returns the value for the named label, or None if an error occurs."""