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Port the LZX and XPRESS decompressors from the userspace ntfs-3g-system-compression plugin (Eric Biggers, https://github.com/ebiggers/ntfs-3g-system-compression) into the in-tree NTFS driver under lib/, and adapt them to the kernel environment. The upstream plugin implements WOF ("Windows Overlay Filesystem", a.k.a. system compression / "Compact OS") decompression for the NTFS-3G FUSE driver, and itself borrows the LZX/XPRESS decompressors that the same author wrote for wimlib (https://wimlib.net/). The XPRESS and LZX formats used here are identical to those used in WIM archives. This commit is the kernel-side port that lets fs/ntfs/wof.c read system-compressed files. The library keeps the upstream subtable-based Huffman decoder (root table + contiguous subtables decoded with MAKE_DECODE_TABLE_ENTRY()), so long codewords only need one extra lookup instead of bit-by-bit tree traversal. The ntfs_codec_ops interface exported to fs/ntfs/wof.c (ntfs_lzx32k_codec_ops and ntfs_xpress{4k,8k,16k}_codec_ops) matches what the WOF layer expects. Modifications made while porting from the upstream plugin: - Replace the variable LZX window order (2^15..2^21) with a fixed 32768-byte window, which is the only size WOF uses - Simplify the bitstream helper: - bitstream_ensure_bits() now guarantees 16 valid bits instead of the carried-over 17-bit refill path from wimlib. Neither LZX (max codeword length 16) nor XPRESS (max 15) needs more than 16 bits. - Refactor codes to satisfy checkpatch. Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com> Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
30 lines
1.1 KiB
C
30 lines
1.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* lib.h - Public declarations for the LZX and XPRESS decompressors.
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*
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* Adapted for the linux kernel. These are the low-level decompressor
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* allocations; WOF (system-compressed) access goes through the
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* ntfs_codec_ops interface declared in "../ntfs_codec.h".
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*/
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#ifndef _LINUX_NTFS_LIB_LIB_H
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#define _LINUX_NTFS_LIB_LIB_H
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#include <linux/types.h>
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/* globals from xpress_decompress.c */
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struct xpress_decompressor *xpress_allocate_decompressor(void);
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void xpress_free_decompressor(struct xpress_decompressor *d);
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int xpress_decompress(struct xpress_decompressor *d,
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const void *compressed_data, size_t compressed_size,
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void *uncompressed_data, size_t uncompressed_size);
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/* globals from lzx_decompress.c */
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struct lzx_decompressor *lzx_allocate_decompressor(void);
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void lzx_free_decompressor(struct lzx_decompressor *d);
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int lzx_decompress(struct lzx_decompressor *d, const void *compressed_data,
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size_t compressed_size, void *uncompressed_data,
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size_t uncompressed_size);
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#endif /* _LINUX_NTFS_LIB_LIB_H */
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