fs.expose.fuse: fix opening of files with mode "w+"

fs/base.py

@@ -890,8 +890,6 @@ class FS(object):
 
 def flags_to_mode(flags):
     """Convert an os.O_* flag bitmask into an FS mode string."""    
-    if flags & os.O_EXCL:
-         raise UnsupportedError("open",msg="O_EXCL is not supported")
     if flags & os.O_WRONLY:
         if flags & os.O_TRUNC:
             mode = "w"
@@ -908,4 +906,6 @@ def flags_to_mode(flags):
             mode = "r+"
     else:
         mode = "r"    
+    if flags & os.O_EXCL:
+        mode += "x"
     return mode

fs/expose/fuse/__init__.py

@@ -165,7 +165,10 @@ class FSOperations(Operations):
     @handle_fs_errors
     def create(self, path, mode, fi):
         path = path.decode(NATIVE_ENCODING)
-        fh = self._reg_file(self.fs.open(path,"w"),path)
+        # FUSE doesn't seem to pass correct mode information here - at least,
+        # I haven't figured out how to distinguish between "w" and "w+".
+        # Go with the most permissive option.
+        fh = self._reg_file(self.fs.open(path,"w+"),path)
         fi.fh = fh
         fi.keep_cache = 0