pysize/core/pysize_global_fs_cache.py

   1 import os
   2
   3 # The cache for directories sizes
   4 # {device: {directory_inode: size}}
   5 DEV_DIR_SIZE = {}
   6
   7 # The cache for hardlinks locations
   8 # {device: {hardlink_inode: (directory_inode, basename)}}
   9 # For memory efficiency reasons, we suppose directory_inode lives
  10 # in the same device as hardlink_inode, but this can be defeated with
  11 # mount --bind on files. So if we have the same hardlink device/inode
  12 # in two directories with the same inode on different devices, we may
  13 # count both instances as canonical, and then counting many times the
  14 # hardlink size. But this is very unlikely, unless on purpose, but then
  15 # you get what you deserve :-p
  16 DEV_HLINK_DNAME = {}
  17
  18 def get_dev_ino(path):
  19     """Return (device_number, inode) for path."""
  20     st = os.lstat(path)
  21     return (st.st_dev, st.st_ino)
  22
  23 def _get_inodes(table, dev):
  24     inodes = table.get(dev, None)
  25     if not inodes:
  26         inodes = {}
  27         table[dev] = inodes
  28     return inodes
  29
  30 def cache_add_dir((dev, ino), size):
  31     """Add a directory and its size to the cache."""
  32     inodes = _get_inodes(DEV_DIR_SIZE, dev)
  33     inodes[ino] = size
  34
  35 def cache_add_hardlink(dev, ino, dir_ino, basename):
  36     """Add a hardlink and its location to the cache, and returns True iff the
  37     location should be considered as the canonical location. Unlike for the
  38     canonical location, a hardlink size is 0."""
  39     entry = (dir_ino, basename)
  40     inodes = _get_inodes(DEV_HLINK_DNAME, dev)
  41     cached_entry = inodes.get(ino, None)
  42     if not cached_entry:
  43         inodes[ino] = entry
  44         return True
  45     return cached_entry == entry
  46
  47 def cache_get_dir_size((dev, ino)):
  48     """Retrieve a directory size from the cache."""
  49     inodes = DEV_DIR_SIZE.get(dev, None)
  50     if inodes:
  51         return inodes.get(ino, None)
  52
  53 def drop_caches():
  54     DEV_DIR_SIZE.clear()
  55     DEV_HLINK_DNAME.clear()