lib/bup/hlinkdb.py

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