linux/include/linux/xz.h
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   1/*
   2 * XZ decompressor
   3 *
   4 * Authors: Lasse Collin <lasse.collin@tukaani.org>
   5 *          Igor Pavlov <http://7-zip.org/>
   6 *
   7 * This file has been put into the public domain.
   8 * You can do whatever you want with this file.
   9 */
  10
  11#ifndef XZ_H
  12#define XZ_H
  13
  14#ifdef __KERNEL__
  15#       include <linux/stddef.h>
  16#       include <linux/types.h>
  17#else
  18#       include <stddef.h>
  19#       include <stdint.h>
  20#endif
  21
  22/* In Linux, this is used to make extern functions static when needed. */
  23#ifndef XZ_EXTERN
  24#       define XZ_EXTERN extern
  25#endif
  26
  27/**
  28 * enum xz_mode - Operation mode
  29 *
  30 * @XZ_SINGLE:              Single-call mode. This uses less RAM than
  31 *                          than multi-call modes, because the LZMA2
  32 *                          dictionary doesn't need to be allocated as
  33 *                          part of the decoder state. All required data
  34 *                          structures are allocated at initialization,
  35 *                          so xz_dec_run() cannot return XZ_MEM_ERROR.
  36 * @XZ_PREALLOC:            Multi-call mode with preallocated LZMA2
  37 *                          dictionary buffer. All data structures are
  38 *                          allocated at initialization, so xz_dec_run()
  39 *                          cannot return XZ_MEM_ERROR.
  40 * @XZ_DYNALLOC:            Multi-call mode. The LZMA2 dictionary is
  41 *                          allocated once the required size has been
  42 *                          parsed from the stream headers. If the
  43 *                          allocation fails, xz_dec_run() will return
  44 *                          XZ_MEM_ERROR.
  45 *
  46 * It is possible to enable support only for a subset of the above
  47 * modes at compile time by defining XZ_DEC_SINGLE, XZ_DEC_PREALLOC,
  48 * or XZ_DEC_DYNALLOC. The xz_dec kernel module is always compiled
  49 * with support for all operation modes, but the preboot code may
  50 * be built with fewer features to minimize code size.
  51 */
  52enum xz_mode {
  53        XZ_SINGLE,
  54        XZ_PREALLOC,
  55        XZ_DYNALLOC
  56};
  57
  58/**
  59 * enum xz_ret - Return codes
  60 * @XZ_OK:                  Everything is OK so far. More input or more
  61 *                          output space is required to continue. This
  62 *                          return code is possible only in multi-call mode
  63 *                          (XZ_PREALLOC or XZ_DYNALLOC).
  64 * @XZ_STREAM_END:          Operation finished successfully.
  65 * @XZ_UNSUPPORTED_CHECK:   Integrity check type is not supported. Decoding
  66 *                          is still possible in multi-call mode by simply
  67 *                          calling xz_dec_run() again.
  68 *                          Note that this return value is used only if
  69 *                          XZ_DEC_ANY_CHECK was defined at build time,
  70 *                          which is not used in the kernel. Unsupported
  71 *                          check types return XZ_OPTIONS_ERROR if
  72 *                          XZ_DEC_ANY_CHECK was not defined at build time.
  73 * @XZ_MEM_ERROR:           Allocating memory failed. This return code is
  74 *                          possible only if the decoder was initialized
  75 *                          with XZ_DYNALLOC. The amount of memory that was
  76 *                          tried to be allocated was no more than the
  77 *                          dict_max argument given to xz_dec_init().
  78 * @XZ_MEMLIMIT_ERROR:      A bigger LZMA2 dictionary would be needed than
  79 *                          allowed by the dict_max argument given to
  80 *                          xz_dec_init(). This return value is possible
  81 *                          only in multi-call mode (XZ_PREALLOC or
  82 *                          XZ_DYNALLOC); the single-call mode (XZ_SINGLE)
  83 *                          ignores the dict_max argument.
  84 * @XZ_FORMAT_ERROR:        File format was not recognized (wrong magic
  85 *                          bytes).
  86 * @XZ_OPTIONS_ERROR:       This implementation doesn't support the requested
  87 *                          compression options. In the decoder this means
  88 *                          that the header CRC32 matches, but the header
  89 *                          itself specifies something that we don't support.
  90 * @XZ_DATA_ERROR:          Compressed data is corrupt.
  91 * @XZ_BUF_ERROR:           Cannot make any progress. Details are slightly
  92 *                          different between multi-call and single-call
  93 *                          mode; more information below.
  94 *
  95 * In multi-call mode, XZ_BUF_ERROR is returned when two consecutive calls
  96 * to XZ code cannot consume any input and cannot produce any new output.
  97 * This happens when there is no new input available, or the output buffer
  98 * is full while at least one output byte is still pending. Assuming your
  99 * code is not buggy, you can get this error only when decoding a compressed
 100 * stream that is truncated or otherwise corrupt.
 101 *
 102 * In single-call mode, XZ_BUF_ERROR is returned only when the output buffer
 103 * is too small or the compressed input is corrupt in a way that makes the
 104 * decoder produce more output than the caller expected. When it is
 105 * (relatively) clear that the compressed input is truncated, XZ_DATA_ERROR
 106 * is used instead of XZ_BUF_ERROR.
 107 */
 108enum xz_ret {
 109        XZ_OK,
 110        XZ_STREAM_END,
 111        XZ_UNSUPPORTED_CHECK,
 112        XZ_MEM_ERROR,
 113        XZ_MEMLIMIT_ERROR,
 114        XZ_FORMAT_ERROR,
 115        XZ_OPTIONS_ERROR,
 116        XZ_DATA_ERROR,
 117        XZ_BUF_ERROR
 118};
 119
 120/**
 121 * struct xz_buf - Passing input and output buffers to XZ code
 122 * @in:         Beginning of the input buffer. This may be NULL if and only
 123 *              if in_pos is equal to in_size.
 124 * @in_pos:     Current position in the input buffer. This must not exceed
 125 *              in_size.
 126 * @in_size:    Size of the input buffer
 127 * @out:        Beginning of the output buffer. This may be NULL if and only
 128 *              if out_pos is equal to out_size.
 129 * @out_pos:    Current position in the output buffer. This must not exceed
 130 *              out_size.
 131 * @out_size:   Size of the output buffer
 132 *
 133 * Only the contents of the output buffer from out[out_pos] onward, and
 134 * the variables in_pos and out_pos are modified by the XZ code.
 135 */
 136struct xz_buf {
 137        const uint8_t *in;
 138        size_t in_pos;
 139        size_t in_size;
 140
 141        uint8_t *out;
 142        size_t out_pos;
 143        size_t out_size;
 144};
 145
 146/**
 147 * struct xz_dec - Opaque type to hold the XZ decoder state
 148 */
 149struct xz_dec;
 150
 151/**
 152 * xz_dec_init() - Allocate and initialize a XZ decoder state
 153 * @mode:       Operation mode
 154 * @dict_max:   Maximum size of the LZMA2 dictionary (history buffer) for
 155 *              multi-call decoding. This is ignored in single-call mode
 156 *              (mode == XZ_SINGLE). LZMA2 dictionary is always 2^n bytes
 157 *              or 2^n + 2^(n-1) bytes (the latter sizes are less common
 158 *              in practice), so other values for dict_max don't make sense.
 159 *              In the kernel, dictionary sizes of 64 KiB, 128 KiB, 256 KiB,
 160 *              512 KiB, and 1 MiB are probably the only reasonable values,
 161 *              except for kernel and initramfs images where a bigger
 162 *              dictionary can be fine and useful.
 163 *
 164 * Single-call mode (XZ_SINGLE): xz_dec_run() decodes the whole stream at
 165 * once. The caller must provide enough output space or the decoding will
 166 * fail. The output space is used as the dictionary buffer, which is why
 167 * there is no need to allocate the dictionary as part of the decoder's
 168 * internal state.
 169 *
 170 * Because the output buffer is used as the workspace, streams encoded using
 171 * a big dictionary are not a problem in single-call mode. It is enough that
 172 * the output buffer is big enough to hold the actual uncompressed data; it
 173 * can be smaller than the dictionary size stored in the stream headers.
 174 *
 175 * Multi-call mode with preallocated dictionary (XZ_PREALLOC): dict_max bytes
 176 * of memory is preallocated for the LZMA2 dictionary. This way there is no
 177 * risk that xz_dec_run() could run out of memory, since xz_dec_run() will
 178 * never allocate any memory. Instead, if the preallocated dictionary is too
 179 * small for decoding the given input stream, xz_dec_run() will return
 180 * XZ_MEMLIMIT_ERROR. Thus, it is important to know what kind of data will be
 181 * decoded to avoid allocating excessive amount of memory for the dictionary.
 182 *
 183 * Multi-call mode with dynamically allocated dictionary (XZ_DYNALLOC):
 184 * dict_max specifies the maximum allowed dictionary size that xz_dec_run()
 185 * may allocate once it has parsed the dictionary size from the stream
 186 * headers. This way excessive allocations can be avoided while still
 187 * limiting the maximum memory usage to a sane value to prevent running the
 188 * system out of memory when decompressing streams from untrusted sources.
 189 *
 190 * On success, xz_dec_init() returns a pointer to struct xz_dec, which is
 191 * ready to be used with xz_dec_run(). If memory allocation fails,
 192 * xz_dec_init() returns NULL.
 193 */
 194XZ_EXTERN struct xz_dec *xz_dec_init(enum xz_mode mode, uint32_t dict_max);
 195
 196/**
 197 * xz_dec_run() - Run the XZ decoder
 198 * @s:          Decoder state allocated using xz_dec_init()
 199 * @b:          Input and output buffers
 200 *
 201 * The possible return values depend on build options and operation mode.
 202 * See enum xz_ret for details.
 203 *
 204 * Note that if an error occurs in single-call mode (return value is not
 205 * XZ_STREAM_END), b->in_pos and b->out_pos are not modified and the
 206 * contents of the output buffer from b->out[b->out_pos] onward are
 207 * undefined. This is true even after XZ_BUF_ERROR, because with some filter
 208 * chains, there may be a second pass over the output buffer, and this pass
 209 * cannot be properly done if the output buffer is truncated. Thus, you
 210 * cannot give the single-call decoder a too small buffer and then expect to
 211 * get that amount valid data from the beginning of the stream. You must use
 212 * the multi-call decoder if you don't want to uncompress the whole stream.
 213 */
 214XZ_EXTERN enum xz_ret xz_dec_run(struct xz_dec *s, struct xz_buf *b);
 215
 216/**
 217 * xz_dec_reset() - Reset an already allocated decoder state
 218 * @s:          Decoder state allocated using xz_dec_init()
 219 *
 220 * This function can be used to reset the multi-call decoder state without
 221 * freeing and reallocating memory with xz_dec_end() and xz_dec_init().
 222 *
 223 * In single-call mode, xz_dec_reset() is always called in the beginning of
 224 * xz_dec_run(). Thus, explicit call to xz_dec_reset() is useful only in
 225 * multi-call mode.
 226 */
 227XZ_EXTERN void xz_dec_reset(struct xz_dec *s);
 228
 229/**
 230 * xz_dec_end() - Free the memory allocated for the decoder state
 231 * @s:          Decoder state allocated using xz_dec_init(). If s is NULL,
 232 *              this function does nothing.
 233 */
 234XZ_EXTERN void xz_dec_end(struct xz_dec *s);
 235
 236/*
 237 * Standalone build (userspace build or in-kernel build for boot time use)
 238 * needs a CRC32 implementation. For normal in-kernel use, kernel's own
 239 * CRC32 module is used instead, and users of this module don't need to
 240 * care about the functions below.
 241 */
 242#ifndef XZ_INTERNAL_CRC32
 243#       ifdef __KERNEL__
 244#               define XZ_INTERNAL_CRC32 0
 245#       else
 246#               define XZ_INTERNAL_CRC32 1
 247#       endif
 248#endif
 249
 250#if XZ_INTERNAL_CRC32
 251/*
 252 * This must be called before any other xz_* function to initialize
 253 * the CRC32 lookup table.
 254 */
 255XZ_EXTERN void xz_crc32_init(void);
 256
 257/*
 258 * Update CRC32 value using the polynomial from IEEE-802.3. To start a new
 259 * calculation, the third argument must be zero. To continue the calculation,
 260 * the previously returned value is passed as the third argument.
 261 */
 262XZ_EXTERN uint32_t xz_crc32(const uint8_t *buf, size_t size, uint32_t crc);
 263#endif
 264#endif
 265
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