Add mksparse.py (create sparse files)

misc/mksparse.py

@@ -0,0 +1,105 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""\
+==============================================
+mksparse.py - sparse file / disk image creator
+==============================================
+
+Usage: mksparse.py <imagefile.img> <size>[k|m|g]
+    This will create <imagefile.img> with size <size>. If the suffix is
+not given then the size is in bytes, 'k' stands for kilobytes (1024),
+'m' for megabytes and 'g' for gigabyes (K/M/G are not implemented, one
+can type 000 easy enough).
+
+Simple python script that creates sparse files on unix / Win2k NTFS5.
+This script opens a file for writing, seeks at the desired position
+(or file size) and truncates the file there. Can be handy while
+playing with qemu / bochs / loopback images.
+
+Tested on linux-2.6 only.
+
+Author: Doncho N. Gunchev <gunchev at gmail dot com>
+Based on Brad Watson's work mkimage.py from
+  http://lists.gnu.org/archive/html/qemu-devel/2004-07/msg00733.html
+  http://qemu.dad-answers.com/download/qemu/utilities/QEMU-HD-Create/
+"""
+
+__version__   = "0.1"
+__author__    = "Doncho Gunchev <gunchev@gmail.com>, Brad Watson"
+__depends__   = ['Python-2.4']
+#__copyright__ = """Have to ask Brad Watson, GPL?"""
+
+
+
+def mk_sparse(file_name, file_size):
+    """ Create a sparse file by truncating it at given position"""
+    try:
+        f = open(sys.argv[1],"wb+")
+    except Exception, e:
+        raise Exception("Error: Can't create file '" + file_name + "':\n" + str(e))
+    else:
+        try:
+            # Note that I don't wan (you too) to write() anything in the file
+            # because this will consume at least one sector/block.
+            f.truncate(int(file_size))
+        except Exception, e:
+            f.close() # clean the mess... TODO: more checks if this does not fail?
+            os.unlink(sys.argv[1])
+            raise Exception("Error: Can't truncate '%s'\n%s" % (file_name, str(e)))
+    try: # Hmm, do I need this at all? Maybe yes (judging from the strange errors
+        # that occure in gzip at object destruction)
+        f.close()
+    except Exception, e:
+        raise Exception("Error: Can't close '%s'\n%s" % (file_name, str(e)))
+
+
+
+if __name__ == "__main__":
+    import os.path
+    import re
+    import sys
+
+    if len(sys.argv) != 3:
+        # .pyo (docstrings stripped) workaround
+        print >> sys.stderr, __doc__ and __doc__ or "Usage: mksparse.py <image-name> <size>[kmg]"
+        print >> sys.stderr, "Version:", __version__
+        sys.exit(1)
+
+    # 'Process' command line parameters
+    file_name = sys.argv[1]
+    file_size = sys.argv[2]
+    # validate file size
+    try:
+        (size, dim) = re.match('^(\d+)([KkMmGg])?$', file_size).groups()
+    except Exception, e:
+        print >> sys.stderr, (sys.argv[0] + ': '
+            + "Bad image size given: " + repr(file_size))
+        sys.exit(2)
+
+    # Check if the file exists, -f (force) would be a good parameter
+    if os.path.exists(file_name):
+        print >> sys.stderr, (sys.argv[0] + ': '
+            + ("Error: file (directory) '%s' already exists!" % (file_name)))
+        sys.exit(3)
+
+    dim = dim.lower()
+    # Calculate size in bytes
+    size = long(size)
+    if   dim == 'k':
+        size *= 1024
+    elif dim == 'm':
+        size *= 1024 * 1024
+    elif dim == 'g':
+        size *= 1024 * 1024 * 1024
+    elif dim != None:
+        print >> sys.stderr, (sys.argv[0] + ': '
+            + "Internal error: size modifier " + repr(dim) + " not handled.")
+        sys.exit(4)
+
+    file_size = size
+    try:
+        mk_sparse(file_name, file_size)
+    except Exception, e:
+        print >> sys.stderr, sys.argv[0] + ': ' + str(e)
+        sys.exit(1)