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SquashFS.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import struct
HEADER_FORMAT = "IIiIIHHHHHHqqqqqqqq"
HEADER_SIZE = struct.calcsize(HEADER_FORMAT)
HEADER3_FORMAT = "<IIIIIIIHHHHBBBiqIIIqqqqqqq"
HEADER3_SIZE = struct.calcsize(HEADER3_FORMAT)
HEADER_MAGIC = 0x73717368
HEADER_KEYS = ["s_magic", "inodes", "mkfs_time", "block_size", "fragments", "compression", "block_log",
"flags", "no_ids", "s_major", "s_minor", "root_inode", "bytes_used", "id_table_start",
"xattr_id_table_start", "inode_table_start", "directory_table_start", "fragment_table_start",
"lookup_table_start"]
HEADER3_KEYS = ["s_magic", "inodes", "bytes_used_2", "uid_start_2", "guid_start_2", "inode_table_start_2",
"directory_table_start_2", "s_major", "s_minor", "block_size_1", "block_log", "flags",
"no_uids", "no_guids", "mkfs_time", "root_inode", "block_size", "fragments",
"fragment_table_start_2", "bytes_used", "uid_start", "guid_start", "inode_table_start",
"directory_table_start", "fragment_table_start", "lookup_table_start"]
ZLIB_COMPRESSION = 1
LZMA_COMPRESSION = 2
LZO_COMPRESSION = 3
XZ_COMPRESSION = 4
LZ4_COMPRESSION = 5
ZLIB_FORMAT = "ihh"
ZLIB_SIZE = struct.calcsize(ZLIB_FORMAT)
GZIP_STRATEGIES = ["default", "filtered", "huffman_only", "run_length_encoded", "fixed"]
LZO_FORMAT = "ii"
LZO_SIZE = struct.calcsize(LZO_FORMAT)
LZO_ALGORITHMS = ["lzo1x_1", "lzo1x_1_11", "lzo1x_1_12", "lzo1x_1_15", "lzo1x_999"]
XZ_FORMAT = "ii"
XZ_SIZE = struct.calcsize(XZ_FORMAT)
LZMA_FILTERS = ["x86", "powerpc", "ia64", "arm", "armthumb", "sparc"]
LZ4_FORMAT = "ii"
LZ4_SIZE = struct.calcsize(LZ4_FORMAT)
LZ4_HC = 1
COMPRESSION_STRING = [None, "gzip", "lzma", "lzo", "xz", "lz4"]
# Filesystem flags
SQUASHFS_NOI = (1 << 0)
SQUASHFS_NOD = (1 << 1)
SQUASHFS_CHECK = (1 << 2)
SQUASHFS_NOF = (1 << 3)
SQUASHFS_NO_FRAG = (1 << 4)
SQUASHFS_ALWAYS_FRAG = (1 << 5)
SQUASHFS_DUPLICATE = (1 << 6)
SQUASHFS_EXPORT = (1 << 7)
SQUASHFS_NOX = (1 << 8)
SQUASHFS_NO_XATTR = (1 << 9)
SQUASHFS_COMP_OPT = (1 << 10)
# Flag whether block is compressed or uncompressed, bit is set if block is uncompressed
SQUASHFS_COMPRESSED_BIT = (1 << 15)
################################################################################
###
### parseHeader(fh, offset=0) - Parse SquashFS header located at offset in file
###
### Parameters: fh: file handle
### offset: Optional location of header within file
###
### Returns: Dictionary of header information
###
def parseHeader(fh, offset=0):
### Save current position and seek to start position
startpos = fh.tell()
fh.seek(offset)
block = fh.read(HEADER_SIZE)
### Unpack the header into a dictionary of (key,value) pairs
values = struct.unpack(HEADER_FORMAT, block)
hd = dict(zip(HEADER_KEYS, values))
if hd["s_magic"] != HEADER_MAGIC:
fh.seek(startpos)
return dict({"s_magic": hd["s_magic"]})
### Not a Squashfs 4 superblock, try to read a squashfs 3 superblock
### (compatible with 1 and 2 filesystems)
if hd["s_major"] != 4:
fh.seek(offset)
block = fh.read(HEADER3_SIZE)
values = struct.unpack(HEADER3_FORMAT, block)
hd = dict(zip(HEADER3_KEYS, values))
### Get compression options if compression is used
if hd["flags"] & SQUASHFS_COMP_OPT:
# read size
block = fh.read(2)
size = struct.unpack("H", block)[0]
compressed = not size & SQUASHFS_COMPRESSED_BIT
if not compressed:
size &= ~SQUASHFS_COMPRESSED_BIT
if size and not compressed:
block = fh.read(size)
if hd["compression"] & ZLIB_COMPRESSION and size >= ZLIB_SIZE:
keys = ["compression_level", "window_size", "strategy"]
values = struct.unpack(ZLIB_FORMAT, block)
hd["comp_opts"] = dict(zip(keys, values))
hd["comp_opts"]["strategies"] = []
for i, strategy in enumerate(GZIP_STRATEGIES):
if (hd["comp_opts"]["strategy"] >> i) & 1:
hd["comp_opts"]["strategies"].append(strategy)
elif hd["compression"] & LZO_COMPRESSION and size >= LZO_SIZE:
keys = ["algorithm", "compression_level"]
values = struct.unpack(LZO_FORMAT, block)
hd["comp_opts"] = dict(zip(keys, values))
hd["comp_opts"]["algorithm_name"] = LZO_ALGORITHMS[hd["comp_opts"]["algorithm"]]
elif hd["compression"] & XZ_COMPRESSION and size >= XZ_SIZE:
keys = ["dictionary_size", "flags"]
values = struct.unpack(XZ_FORMAT, block)
hd["comp_opts"] = dict(zip(keys, values))
hd["comp_opts"]["filters"] = []
for i, filter in enumerate(LZMA_FILTERS):
if (hd["comp_opts"]["flags"] >> i) & 1:
hd["comp_opts"]["filters"].append(filter)
elif hd["compression"] & LZ4_COMPRESSION and size >= LZ4_SIZE:
keys = ["version", "flags"]
values = struct.unpack(LZ4_FORMAT, block)
hd["comp_opts"] = dict(zip(keys, values))
hd["comp_opts"]["hc"] = hd["comp_opts"]["flags"] & LZ4_HC
### Restore saved file position
fh.seek(startpos)
return hd
################################################################################
###
### buildConOpts(hd) - Build mksquashfs console options from parsed header
###
### Parameters: hd: Dictionary of header information
###
### Returns: List of console options
###
def buildConOpts(hd):
args = []
if "compression" in hd:
args.extend(("-comp", COMPRESSION_STRING[hd["compression"]]))
args.extend(("-b", str(hd["block_size"])))
if not hd["flags"] & SQUASHFS_EXPORT:
args.append("-no-exports")
if hd["flags"] & SQUASHFS_NO_XATTR:
args.append("-no-xattrs")
if hd["flags"] & SQUASHFS_NOI:
args.append("-noI")
if hd["flags"] & SQUASHFS_NOD:
args.append("-noD")
if hd["flags"] & SQUASHFS_NOF:
args.append("-noF")
if hd["flags"] & SQUASHFS_NOX:
args.append("-noX")
if hd["flags"] & SQUASHFS_NO_FRAG:
args.append("-no-fragments")
if hd["flags"] & SQUASHFS_ALWAYS_FRAG:
args.append("-always-use-fragments")
if not hd["flags"] & SQUASHFS_DUPLICATE:
args.append("-no-duplicates")
if not "comp_opts" in hd:
return args
if hd["compression"] & ZLIB_COMPRESSION:
args.extend(("-Xcompression-level", str(hd["comp_opts"]["compression_level"])))
args.extend(("-Xwindow-size", str(hd["comp_opts"]["window_size"])))
args.extend(("-Xstrategy", ','.join(hd["comp_opts"]["strategies"])))
elif hd["compression"] & LZO_COMPRESSION:
args.extend(("-Xalgorithm", str(hd["comp_opts"]["algorithm_name"])))
args.extend(("-Xcompression-level", str(hd["comp_opts"]["compression_level"])))
elif hd["compression"] & XZ_COMPRESSION:
args.extend(("-Xbcj", ','.join(hd["comp_opts"]["filters"])))
args.extend(("-Xdict-size", str(hd["comp_opts"]["dictionary_size"])))
elif hd["compression"] & LZ4_COMPRESSION:
if hd["comp_opts"]["hc"]:
args.extend("-Xhc")
return args