xend: improve the rotation of qemu-dm logfiles.

Signed-off-by: Yosuke Iwamatsu <y-iwamatsu@ab.jp.nec.com>

diff -r 926a366ca82f tools/python/xen/xend/image.py
--- a/tools/python/xen/xend/image.py	Fri Jun 20 15:21:26 2008 +0100
+++ b/tools/python/xen/xend/image.py	Fri Jun 27 16:54:40 2008 +0900
@@ -378,9 +378,16 @@ class ImageHandler:
         # keep track of pid and spawned options to kill it later
 
         self.logfile = "/var/log/xen/qemu-dm-%s.log" %  str(self.vm.info['name_label'])
+
+        # rotate log
+        nr_max_log_rotation = 20
+        if os.path.exists(self.logfile + ".%d" % nr_max_log_rotation):
+            os.unlink(self.logfile + ".%d" % nr_max_log_rotation)
+        for n in range(nr_max_log_rotation - 1, 0, -1):
+            if os.path.exists(self.logfile + ".%d" % n):
+                os.rename(self.logfile + ".%d" % n,
+                          self.logfile + ".%d" % (n + 1))
         if os.path.exists(self.logfile):
-            if os.path.exists(self.logfile + ".1"):
-                os.unlink(self.logfile + ".1")
             os.rename(self.logfile, self.logfile + ".1")
 
         null = os.open("/dev/null", os.O_RDONLY)