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 Guillaume Chazarain <guichaz@yahoo.fr>
  18
  19 import os
  20
  21 # The cache for directories sizes
  22 # {device: {directory_inode: size}}
  23 DEV_DIR_SIZE = {}
  24
  25 # The cache for hardlinks locations
  26 # {device: {hardlink_inode: (directory_inode, basename)}}
  27 # For memory efficiency reasons, we suppose directory_inode lives
  28 # in the same device as hardlink_inode, but this can be defeated with
  29 # mount --bind on files. So if we have the same hardlink device/inode
  30 # in two directories with the same inode on different devices, we may
  31 # count both instances as canonical, and then counting many times the
  32 # hardlink size. But this is very unlikely, unless on purpose, but then
  33 # you get what you deserve :-p
  34 DEV_HLINK_DNAME = {}
  35
  36 def get_dev_ino(path):
  37     """Return (device_number, inode) for path."""
  38     st = os.lstat(path)
  39     return st.st_dev, st.st_ino
  40
  41 def cache_add_dir((dev, ino), size):
  42     """Add a directory and its size to the cache."""
  43     inodes = DEV_DIR_SIZE.setdefault(dev, {})
  44     inodes[ino] = size
  45
  46 def cache_add_hardlink(dev, ino, dir_ino, basename):
  47     """Add a hardlink and its location to the cache, and returns True iff the
  48     location should be considered as the canonical location. Unlike for the
  49     canonical location, a hardlink size is 0."""
  50     entry = dir_ino, basename
  51     inodes = DEV_HLINK_DNAME.setdefault(dev, {})
  52     cached_entry = inodes.setdefault(ino, entry)
  53     return cached_entry == entry
  54
  55 def cache_get_dir_size((dev, ino)):
  56     """Retrieve a directory size from the cache."""
  57     inodes = DEV_DIR_SIZE.get(dev, None)
  58     if inodes:
  59         return inodes.get(ino, None)
  60
  61 def drop_caches():
  62     DEV_DIR_SIZE.clear()
  63     DEV_HLINK_DNAME.clear()