1 files changed, 31 insertions, 0 deletions
diff --git a/xlators/features/marker/utils/syncdaemon/syncdutils.py b/xlators/features/marker/utils/syncdaemon/syncdutils.py
index 52dad8c5ff3..723ab8fb5fc 100644
--- a/xlators/features/marker/utils/syncdaemon/syncdutils.py
+++ b/xlators/features/marker/utils/syncdaemon/syncdutils.py
@@ -1,3 +1,5 @@
+import os
+import fcntl
 try:
     # py 3
     from urllib import parse as urllib
@@ -9,3 +11,32 @@ def escape(s):
 
 def unescape(s):
     return urllib.unquote_plus(s)
+
+def update_file(path, updater, merger = lambda f: True):
+    """update a file in a transaction-like manner"""
+
+    fr = fw = None
+    try:
+        fd = os.open(path, os.O_CREAT|os.O_RDWR)
+        try:
+            fr = os.fdopen(fd, 'r+b')
+        except:
+            os.close(fd)
+            raise
+        fcntl.lockf(fr, fcntl.LOCK_EX)
+        merger(fr)
+
+        tmpp = path + '.tmp.' + str(os.getpid())
+        fd = os.open(tmpp, os.O_CREAT|os.O_EXCL|os.O_WRONLY)
+        try:
+            fw = os.fdopen(fd, 'wb', 0)
+        except:
+            os.close(fd)
+            raise
+        updater(fw)
+        os.fsync(fd)
+        os.rename(tmpp, path)
+    finally:
+        for fx in (fr, fw):
+            if fx:
+                fx.close()