site_scons/site_tools/windows_hard_link.py

   1 #!/usr/bin/python2.4
   2 # Copyright 2009, Google Inc.
   3 # All rights reserved.
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   7 # met:
   8 #
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  10 # notice, this list of conditions and the following disclaimer.
  11 #     * Redistributions in binary form must reproduce the above
  12 # copyright notice, this list of conditions and the following disclaimer
  13 # in the documentation and/or other materials provided with the
  14 # distribution.
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  16 # contributors may be used to endorse or promote products derived from
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  18 #
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  20 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  22 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  23 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  29 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30
  31 """Hard link support for Windows.
  32
  33 This module is a SCons tool which should be include in the topmost windows
  34 environment.  It is usually included by the target_platform_windows tool.
  35 """
  36
  37
  38 import os
  39 import stat
  40 import sys
  41 import SCons
  42
  43 if sys.platform == 'win32':
  44   # Only attempt to load pywin32 on Windows systems
  45   try:
  46     import win32file
  47   except ImportError:
  48     print ('Warning: Unable to load win32file module; using copy instead of'
  49            ' hard linking for env.Install().  Is pywin32 present?')
  50
  51 #------------------------------------------------------------------------------
  52 # Python 2.4 and 2.5's os module doesn't support os.link on Windows, even
  53 # though Windows does have hard-link capability on NTFS filesystems.  So by
  54 # default, SCons will insist on copying files instead of linking them as it
  55 # does on other (linux,mac) OS's.
  56 #
  57 # Use the CreateHardLink() functionality from pywin32 to provide hard link
  58 # capability on Windows also.
  59
  60
  61 def _HardLink(fs, src, dst):
  62   """Hard link function for hooking into SCons.Node.FS.
  63
  64   Args:
  65     fs: Filesystem class to use.
  66     src: Source filename to link to.
  67     dst: Destination link name to create.
  68
  69   Raises:
  70     OSError: The link could not be created.
  71   """
  72   # A hard link shares file permissions from the source.  On Windows, the write
  73   # access of the file itself determines whether the file can be deleted
  74   # (unlike Linux/Mac, where it's the write access of the containing
  75   # directory).  So if we made a link from a read-only file, the only way to
  76   # delete it would be to make the link writable, which would have the
  77   # unintended effect of making the source writable too.
  78   #
  79   # So if the source is read-only, we can't hard link from it.
  80   if not stat.S_IMODE(fs.stat(src)[stat.ST_MODE]) & stat.S_IWRITE:
  81     raise OSError('Unsafe to hard-link read-only file: %s' % src)
  82
  83   # If the file is writable, only hard-link from it if it was build by SCons.
  84   # Those files shouldn't later become read-only.  We don't hard-link from
  85   # writable files which SCons didn't create, because those could become
  86   # read-only (for example, following a 'p4 submit'), which as indicated above
  87   # would make our link read-only too.
  88   if not fs.File(src).has_builder():
  89     raise OSError('Unsafe to hard-link file not built by SCons: %s' % src)
  90
  91   try:
  92     win32file.CreateHardLink(dst, src)
  93   except win32file.error, msg:
  94     # Translate errors into standard OSError which SCons expects.
  95     raise OSError(msg)
  96
  97
  98 #------------------------------------------------------------------------------
  99
 100
 101 def generate(env):
 102   # NOTE: SCons requires the use of this name, which fails gpylint.
 103   """SCons entry point for this tool."""
 104   env = env  # Silence gpylint
 105
 106   # Patch in our hard link function, if we were able to load pywin32
 107   if 'win32file' in globals():
 108     SCons.Node.FS._hardlink_func = _HardLink