pysize/core/pysize_global_fs_cache.py

   1 # This program is free software; you can redistribute it and/or modify
   2 # it under the terms of the GNU General Public License as published by
   3 # the Free Software Foundation; either version 2 of the License, or
   4 # (at your option) any later version.
   5 #
   6 # This program is distributed in the hope that it will be useful,
   7 # but WITHOUT ANY WARRANTY; without even the implied warranty of
   8 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   9 # GNU Library General Public License for more details.
  10 #
  11 # You should have received a copy of the GNU General Public License
  12 # along with this program; if not, write to the Free Software
  13 # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  14 #
  15 # See the COPYING file for license information.
  16 #
  17 # Copyright (c) 2006, 2007, 2008  Guillaume Chazarain <guichaz@gmail.com>
  18
  19 import os
  20 from pysize.core.exception_propagation import raises
  21
  22 # The cache for directories sizes
  23 # {device: {directory_inode: size}}
  24 DEV_DIR_SIZE = {}
  25
  26 # The cache for hardlinks locations
  27 # {device: {hardlink_inode: (directory_inode, basename)}}
  28 # For memory efficiency reasons, we suppose directory_inode lives
  29 # in the same device as hardlink_inode, but this can be defeated with
  30 # mount --bind on files. So if we have the same hardlink device/inode
  31 # in two directories with the same inode on different devices, we may
  32 # count both instances as canonical, and then counting many times the
  33 # hardlink size. But this is very unlikely, unless on purpose, but then
  34 # you get what you deserve :-p
  35 DEV_HLINK_DNAME = {}
  36
  37 @raises(OSError)
  38 def get_dev_ino(path):
  39     """Return (device_number, inode) for path."""
  40     st = os.lstat(path)
  41     return st.st_dev, st.st_ino
  42
  43 def cache_add_dir((dev, ino), size):
  44     """Add a directory and its size to the cache."""
  45     inodes = DEV_DIR_SIZE.setdefault(dev, {})
  46     inodes[ino] = size
  47
  48 def cache_add_hardlink(dev, ino, dir_ino, path):
  49     """Add a hardlink and its location to the cache, and returns True iff the
  50     location should be considered as the canonical location. Unlike for the
  51     canonical location, a hardlink size is 0."""
  52     entry = dir_ino, os.path.basename(path)
  53     inodes = DEV_HLINK_DNAME.setdefault(dev, {})
  54     cached_entry = inodes.setdefault(ino, entry)
  55     return cached_entry == entry
  56
  57 def cache_get_dir_size((dev, ino)):
  58     """Retrieve a directory size from the cache."""
  59     inodes = DEV_DIR_SIZE.get(dev, None)
  60     if inodes:
  61         return inodes.get(ino, None)
  62
  63 def drop_caches():
  64     DEV_DIR_SIZE.clear()
  65     DEV_HLINK_DNAME.clear()