[Kimchi-devel] [PATCH][Wok] Add support to timestamps in clone naming function

[Rodrigo Trujillo]

There is a potential race condiction issue when some plugin tries to use
the function get_next_clone_name(all_names, basename, name_suffix='').
If clone requests are done so fast, it is possible that the plugin does
not send all resource names in all_names parameter, then the function is
going to select the same name for 2 or more clones, which is going to
cause errors in the plugin.

Supporting timestamps in microsecond precision, plugins can avoid this
type of error coding its own race condiction fix or just using the
timestamp function option.
New name will be "basename-clone-timestamp-name-suffix".

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo at linux.vnet.ibm.com>
---
 src/wok/utils.py | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/wok/utils.py b/src/wok/utils.py
index 7e9a928..b80a80b 100644
--- a/src/wok/utils.py
+++ b/src/wok/utils.py
@@ -31,6 +31,7 @@ import re
 import sqlite3
 import subprocess
 import sys
+import time
 import traceback
 import xml.etree.ElementTree as ET
 
@@ -391,7 +392,7 @@ def remove_old_files(globexpr, hours):
         wok_log.error(str(e))
 
 
-def get_next_clone_name(all_names, basename, name_suffix=''):
+def get_next_clone_name(all_names, basename, name_suffix='', ts=False):
     """Find the next available name for a cloned resource.
 
     If any resource named "<basename>-clone-<number><name_suffix>" is found
@@ -406,26 +407,34 @@ def get_next_clone_name(all_names, basename, name_suffix=''):
         exist so that a resource named "foo.img" gets the name
         "foo-clone-1.img" instead of "foo.img-clone-1". If this parameter
         is used, the suffix should not be present in "basename".
+    ts -- use timestamp, instead of incremental numbers
 
     Return:
     A UTF-8 string in the format "<basename>-clone-<number><name_suffix>".
     """
     re_group_num = 'num'
 
-    re_expr = u'%s-clone-(?P<%s>\d+)' % (basename, re_group_num)
-    if name_suffix != '':
-        re_expr = u'%s%s' % (re_expr, name_suffix)
+    # Use timestamps or increase clone number
+    if ts:
+        # Microsecond precision
+        ts_suffix = int(time.time() * 1000000)
+        new_name = u'%s-clone-%d' % (basename, ts_suffix)
+    else:
+        re_expr = u'%s-clone-(?P<%s>\d+)' % (basename, re_group_num)
+        if name_suffix != '':
+            re_expr = u'%s%s' % (re_expr, name_suffix)
 
-    max_num = 0
-    re_compiled = re.compile(re_expr)
+        max_num = 0
+        re_compiled = re.compile(re_expr)
 
-    for n in all_names:
-        match = re_compiled.match(n)
-        if match is not None:
-            max_num = max(max_num, int(match.group(re_group_num)))
+        for n in all_names:
+            match = re_compiled.match(n)
+            if match is not None:
+                max_num = max(max_num, int(match.group(re_group_num)))
+
+        # increments the maximum "clone number" found
+        new_name = u'%s-clone-%d' % (basename, max_num + 1)
 
-    # increments the maximum "clone number" found
-    new_name = u'%s-clone-%d' % (basename, max_num + 1)
     if name_suffix != '':
         new_name = new_name + name_suffix
 
-- 
2.1.0