Merge branch 'improve-mode-handling' of https://github.com/Firstyear/osc

Only change the mode of a config file if it is different from 0o600 (instead
of unconditionally calling os.chmod). The advantage of the new behavior is
that it also works with a read-only filesystem. Additionally, if the mode
is not 0o600 and the config file resides on a read-only filesystem, we
print a warning and continue (actually, this change is debatable but it is
also not too bad because the config file does not necessarily have to
contain the passwords anymore... (let's keep our fingers crossed that no
3rd party application relied on the "implicit" os.chmod API, though)).

osc/conf.py

@@ -38,6 +38,7 @@ The configuration dictionary could look like this:
 
 import bz2
 import base64
+import errno
 import os
 import re
 import sys
@@ -896,7 +897,15 @@ def get_config(override_conffile=None,
     # okay, we made sure that oscrc exists
 
     # make sure it is not world readable, it may contain a password.
-    os.chmod(conffile, 0o600)
+    conffile_stat = os.stat(conffile)
+    if conffile_stat.st_mode != 0o600:
+        try:
+            os.chmod(conffile, 0o600)
+        except OSError as e:
+            if e.errno == errno.EROFS:
+                print('Warning: file \'%s\' may have an insecure mode.', conffile)
+            else:
+                raise e
 
     cp = get_configParser(conffile)