lib/bup/hlinkdb.py

   1 import cPickle, errno, os, tempfile
   2
   3 class Error(Exception):
   4     pass
   5
   6 class HLinkDB:
   7     def __init__(self, filename):
   8         # Map a "dev:ino" node to a list of paths associated with that node.
   9         self._node_paths = {}
  10         # Map a path to a "dev:ino" node.
  11         self._path_node = {}
  12         self._filename = filename
  13         self._save_prepared = None
  14         self._tmpname = None
  15         f = None
  16         try:
  17             f = open(filename, 'r')
  18         except IOError, e:
  19             if e.errno == errno.ENOENT:
  20                 pass
  21             else:
  22                 raise
  23         if f:
  24             try:
  25                 self._node_paths = cPickle.load(f)
  26             finally:
  27                 f.close()
  28                 f = None
  29         # Set up the reverse hard link index.
  30         for node, paths in self._node_paths.iteritems():
  31             for path in paths:
  32                 self._path_node[path] = node
  33
  34     def prepare_save(self):
  35         """ Commit all of the relevant data to disk.  Do as much work
  36         as possible without actually making the changes visible."""
  37         if self._save_prepared:
  38             raise Error('save of %r already in progress' % self._filename)
  39         if self._node_paths:
  40             (dir, name) = os.path.split(self._filename)
  41             (ffd, self._tmpname) = tempfile.mkstemp('.tmp', name, dir)
  42             try:
  43                 f = os.fdopen(ffd, 'wb', 65536)
  44             except:
  45                 os.close(ffd)
  46                 raise
  47             try:
  48                 cPickle.dump(self._node_paths, f, 2)
  49             except:
  50                 f.close()
  51                 os.unlink(self._tmpname)
  52                 self._tmpname = None
  53                 raise
  54             else:
  55                 f.close()
  56                 f = None
  57         self._save_prepared = True
  58
  59     def commit_save(self):
  60         if not self._save_prepared:
  61             raise Error('cannot commit save of %r; no save prepared'
  62                         % self._filename)
  63         if self._tmpname:
  64             os.rename(self._tmpname, self._filename)
  65             self._tmpname = None
  66         else: # No data -- delete _filename if it exists.
  67             try:
  68                 os.unlink(self._filename)
  69             except OSError, e:
  70                 if e.errno == errno.ENOENT:
  71                     pass
  72                 else:
  73                     raise
  74         self._save_prepared = None
  75
  76     def abort_save(self):
  77         if self._tmpname:
  78             os.unlink(self._tmpname)
  79             self._tmpname = None
  80
  81     def __del__(self):
  82         self.abort_save()
  83
  84     def add_path(self, path, dev, ino):
  85         # Assume path is new.
  86         node = '%s:%s' % (dev, ino)
  87         self._path_node[path] = node
  88         link_paths = self._node_paths.get(node)
  89         if link_paths and path not in link_paths:
  90             link_paths.append(path)
  91         else:
  92             self._node_paths[node] = [path]
  93
  94     def _del_node_path(self, node, path):
  95         link_paths = self._node_paths[node]
  96         link_paths.remove(path)
  97         if not link_paths:
  98             del self._node_paths[node]
  99
 100     def change_path(self, path, new_dev, new_ino):
 101         prev_node = self._path_node.get(path)
 102         if prev_node:
 103             self._del_node_path(prev_node, path)
 104         self.add_path(new_dev, new_ino, path)
 105
 106     def del_path(self, path):
 107         # Path may not be in db (if updating a pre-hardlink support index).
 108         node = self._path_node.get(path)
 109         if node:
 110             self._del_node_path(node, path)
 111             del self._path_node[path]
 112
 113     def node_paths(self, dev, ino):
 114         node = '%s:%s' % (dev, ino)
 115         return self._node_paths[node]