+# replace a target file with a new contents - checks for changes
+# return True if a change occurred, in which case
+# chown/chmod settings should be taken care of
+def replace_file_with_string (target, new_contents, chmod=None, remove_if_empty=False):
+ try:
+ current=file(target).read()
+ except:
+ current=""
+ if current==new_contents:
+ # if turns out to be an empty string, and remove_if_empty is set,
+ # then make sure to trash the file if it exists
+ if remove_if_empty and not new_contents and os.path.isfile(target):
+ logger.verbose("tools.replace_file_with_string: removing file %s"%target)
+ try: os.unlink(target)
+ finally: return True
+ return False
+ # overwrite target file
+ f=file(target,'w')
+ f.write(new_contents)
+ f.close()
+ if chmod: os.chmod(target,chmod)
+ return True
+
+# not needed yet - should that unlink the new file ?
+#def replace_file_with_file (target, new):
+# return replace_file_with_string (target, file(new).read())
+
+####################
+# utilities functions to get (cached) information from the node
+
+# get node_id from /etc/planetlab/node_id and cache it
+_node_id=None
+def node_id():
+ global _node_id
+ if _node_id is None:
+ try:
+ _node_id=int(file("/etc/planetlab/node_id").read())
+ except:
+ _node_id=""
+ return _node_id
+
+_root_context_arch=None
+def root_context_arch():
+ global _root_context_arch
+ if not _root_context_arch:
+ sp=subprocess.Popen(["uname","-i"],stdout=subprocess.PIPE)
+ (_root_context_arch,_)=sp.communicate()
+ _root_context_arch=_root_context_arch.strip()
+ return _root_context_arch
+