mirror of
https://github.com/elliotnunn/NetBoot.git
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128 lines
4.6 KiB
Python
Executable File
128 lines
4.6 KiB
Python
Executable File
#!/usr/bin/env python3
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# MIT License
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# Copyright (c) 2018 Elliot Nunn
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in all
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# copies or substantial portions of the Software.
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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import struct
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def alignment(num):
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# count trailing zero bits to a max of 32
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for i in reversed(range(33)):
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if num & ((1 << i) - 1) == 0: return i
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def bitmap_len(drNmAlBlks):
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# how many bytes occupied by the 512b blocks required to make up n bits?
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num_512s = (drNmAlBlks + 4095) // 4096
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return num_512s * 512
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def resize(img, freespace):
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drVBMSt, = struct.unpack_from('>H', img, 0x40E)
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drNmAlBlks, = struct.unpack_from('>H', img, 0x412)
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drAlBlkSiz, = struct.unpack_from('>L', img, 0x414)
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drAlBlSt, = struct.unpack_from('>H', img, 0x41C)
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drFreeBks, = struct.unpack_from('>H', img, 0x422)
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align = alignment(drAlBlSt)
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header = bytearray(img[:0x600])
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bitmap = img[drVBMSt*512:drVBMSt*512+bitmap_len(drNmAlBlks)]
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guts = img[drAlBlSt*512:drAlBlSt*512+drNmAlBlks*drAlBlkSiz]
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# Decide how much to shrink
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drFreeBks -= drNmAlBlks
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for drNmAlBlks in range(drNmAlBlks, 0, -1):
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byte = bitmap[(drNmAlBlks-1) >> 3]
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mask = 0x80 >> ((drNmAlBlks-1) & 7)
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if byte & mask: break
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drFreeBks += drNmAlBlks
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# Decide how much to expand
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while drNmAlBlks < 0xffff and drFreeBks * drAlBlkSiz < freespace:
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drFreeBks += 1
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drNmAlBlks += 1
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# Resize components
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bitmap = bitmap[:bitmap_len(drNmAlBlks)].ljust(bitmap_len(drNmAlBlks), b'\0')
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guts = guts[:drNmAlBlks*drAlBlkSiz].ljust(drNmAlBlks*drAlBlkSiz, b'\0')
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# Reposition the guts after the bitmap, preserving original alignment
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drAlBlSt = 3 + len(bitmap)//512
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while alignment(drAlBlSt) < align: drAlBlSt += 1
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struct.pack_into('>H', header, 0x40E, len(header)//512) # drVBMSt
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struct.pack_into('>H', header, 0x412, drNmAlBlks)
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struct.pack_into('>H', header, 0x41C, drAlBlSt)
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struct.pack_into('>H', header, 0x422, drFreeBks)
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accum = bytearray()
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accum.extend(header)
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accum.extend(bitmap)
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accum.extend(bytes(drAlBlSt*512 - len(accum)))
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accum.extend(guts)
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accum.extend(header[0x400:0x800])
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accum.extend(bytes(512))
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return accum
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if __name__ == '__main__':
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import sys
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import argparse
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parser = argparse.ArgumentParser(description='''
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Resize an HFS disk image by adding/removing allocation blocks.
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Warning: only images from `machfs` can be shrunk, because the
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real MacOS uses the allocation blocks at the end of the disk.
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''')
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parser.add_argument('diskimage', metavar='PATH', action='store', help='disk image')
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parser.add_argument('--freespace', metavar='BYTES', action='store', type=int, default=0, help='free space target (0 means shrink)')
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parser.add_argument('--verbose', '-v', action='store_true', help='print stats')
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args = parser.parse_args()
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with open(args.diskimage, 'rb') as f:
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oldimage = f.read()
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if oldimage[1024:1026] != b'BD': sys.exit('Not an HFS volume')
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newimage = resize(oldimage, args.freespace)
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if args.verbose:
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for kind, img in (('old', oldimage), ('new', newimage)):
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drNmAlBlks, = struct.unpack_from('>H', img, 0x412)
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drFreeBks, = struct.unpack_from('>H', img, 0x422)
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print(kind, 'bytes: ', len(img))
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print(kind, 'drNmAlBlks: ', drNmAlBlks)
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print(kind, 'drFreeBks: ', drFreeBks)
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print('percentage size:', 100 * len(newimage) // len(oldimage))
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print('changed: ', ('no' if newimage == oldimage else 'yes'))
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if newimage != oldimage:
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with open(args.diskimage, 'wb') as f:
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f.write(newimage)
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