add 'run_per_instance' to CloudConfig

This method aloows the caller to run easily run something
"once per instance".  Its location in CloudConfig rather than
'util' is really only because it needs access to cloudinit.get_ipath_cur
to get the 'data' path.

1 files changed, 12 insertions, 0 deletions

diff --git a/cloudinit/CloudConfig/__init__.py b/cloudinit/CloudConfig/__init__.py
index 7b01f00a..c8743ac3 100644
--- a/cloudinit/CloudConfig/__init__.py
+++ b/cloudinit/CloudConfig/__init__.py
@@ -23,6 +23,7 @@ import sys
 import traceback
 import os
 import subprocess
+import time
 
 per_instance="once-per-instance"
 per_always="always"
@@ -219,3 +220,14 @@ def redirect_output(outfmt,errfmt, o_out=sys.stdout, o_err=sys.stderr):
         if o_err:
             os.dup2(new_fp.fileno(), o_err.fileno())
     return
+
+def run_per_instance(name, func, args, clear_on_fail=False):
+    semfile = "%s/%s" % (cloudinit.get_ipath_cur("data"),name)
+    if os.path.exists(semfile): return
+
+    util.write_file(semfile,str(time.time()))
+    try:
+        func(*args)
+    except:
+        if clear_on_fail: os.unlink(semfile)
+        raise