diff options
Diffstat (limited to 'archival/libunarchive/unxz/xz.h')
| -rw-r--r-- | archival/libunarchive/unxz/xz.h | 139 |
1 files changed, 94 insertions, 45 deletions
diff --git a/archival/libunarchive/unxz/xz.h b/archival/libunarchive/unxz/xz.h index eb82706..c6c071c 100644 --- a/archival/libunarchive/unxz/xz.h +++ b/archival/libunarchive/unxz/xz.h @@ -30,9 +30,42 @@ #endif /** + * enum xz_mode - Operation mode + * + * @XZ_SINGLE: Single-call mode. This uses less RAM than + * than multi-call modes, because the LZMA2 + * dictionary doesn't need to be allocated as + * part of the decoder state. All required data + * structures are allocated at initialization, + * so xz_dec_run() cannot return XZ_MEM_ERROR. + * @XZ_PREALLOC: Multi-call mode with preallocated LZMA2 + * dictionary buffer. All data structures are + * allocated at initialization, so xz_dec_run() + * cannot return XZ_MEM_ERROR. + * @XZ_DYNALLOC: Multi-call mode. The LZMA2 dictionary is + * allocated once the required size has been + * parsed from the stream headers. If the + * allocation fails, xz_dec_run() will return + * XZ_MEM_ERROR. + * + * It is possible to enable support only for a subset of the above + * modes at compile time by defining XZ_DEC_SINGLE, XZ_DEC_PREALLOC, + * or XZ_DEC_DYNALLOC. The xz_dec kernel module is always compiled + * with support for all operation modes, but the preboot code may + * be built with fewer features to minimize code size. + */ +enum xz_mode { + XZ_SINGLE, + XZ_PREALLOC, + XZ_DYNALLOC +}; + +/** * enum xz_ret - Return codes * @XZ_OK: Everything is OK so far. More input or more - * output space is required to continue. + * output space is required to continue. This + * return code is possible only in multi-call mode + * (XZ_PREALLOC or XZ_DYNALLOC). * @XZ_STREAM_END: Operation finished successfully. * @XZ_UNSUPPORTED_CHECK: Integrity check type is not supported. Decoding * is still possible in multi-call mode by simply @@ -42,8 +75,17 @@ * which is not used in the kernel. Unsupported * check types return XZ_OPTIONS_ERROR if * XZ_DEC_ANY_CHECK was not defined at build time. - * @XZ_MEMLIMIT_ERROR: Not enough memory was preallocated at decoder - * initialization time. + * @XZ_MEM_ERROR: Allocating memory failed. This return code is + * possible only if the decoder was initialized + * with XZ_DYNALLOC. The amount of memory that was + * tried to be allocated was no more than the + * dict_max argument given to xz_dec_init(). + * @XZ_MEMLIMIT_ERROR: A bigger LZMA2 dictionary would be needed than + * allowed by the dict_max argument given to + * xz_dec_init(). This return value is possible + * only in multi-call mode (XZ_PREALLOC or + * XZ_DYNALLOC); the single-call mode (XZ_SINGLE) + * ignores the dict_max argument. * @XZ_FORMAT_ERROR: File format was not recognized (wrong magic * bytes). * @XZ_OPTIONS_ERROR: This implementation doesn't support the requested @@ -72,6 +114,7 @@ enum xz_ret { XZ_OK, XZ_STREAM_END, XZ_UNSUPPORTED_CHECK, + XZ_MEM_ERROR, XZ_MEMLIMIT_ERROR, XZ_FORMAT_ERROR, XZ_OPTIONS_ERROR, @@ -112,61 +155,67 @@ struct xz_dec; /** * xz_dec_init() - Allocate and initialize a XZ decoder state + * @mode: Operation mode * @dict_max: Maximum size of the LZMA2 dictionary (history buffer) for - * multi-call decoding, or special value of zero to indicate - * single-call decoding mode. - * - * If dict_max > 0, the decoder is initialized to work in multi-call mode. - * dict_max number of bytes of memory is preallocated for the LZMA2 - * dictionary. This way there is no risk that xz_dec_run() could run out - * of memory, since xz_dec_run() will never allocate any memory. Instead, - * if the preallocated dictionary is too small for decoding the given input - * stream, xz_dec_run() will return XZ_MEMLIMIT_ERROR. Thus, it is important - * to know what kind of data will be decoded to avoid allocating excessive - * amount of memory for the dictionary. - * - * LZMA2 dictionary is always 2^n bytes or 2^n + 2^(n-1) bytes (the latter - * sizes are less common in practice). In the kernel, dictionary sizes of - * 64 KiB, 128 KiB, 256 KiB, 512 KiB, and 1 MiB are probably the only - * reasonable values. - * - * If dict_max == 0, the decoder is initialized to work in single-call mode. - * In single-call mode, xz_dec_run() decodes the whole stream at once. The - * caller must provide enough output space or the decoding will fail. The - * output space is used as the dictionary buffer, which is why there is - * no need to allocate the dictionary as part of the decoder's internal - * state. + * multi-call decoding. This is ignored in single-call mode + * (mode == XZ_SINGLE). LZMA2 dictionary is always 2^n bytes + * or 2^n + 2^(n-1) bytes (the latter sizes are less common + * in practice), so other values for dict_max don't make sense. + * In the kernel, dictionary sizes of 64 KiB, 128 KiB, 256 KiB, + * 512 KiB, and 1 MiB are probably the only reasonable values, + * except for kernel and initramfs images where a bigger + * dictionary can be fine and useful. + * + * Single-call mode (XZ_SINGLE): xz_dec_run() decodes the whole stream at + * once. The caller must provide enough output space or the decoding will + * fail. The output space is used as the dictionary buffer, which is why + * there is no need to allocate the dictionary as part of the decoder's + * internal state. * * Because the output buffer is used as the workspace, streams encoded using - * a big dictionary are not a problem in single-call. It is enough that the - * output buffer is big enough to hold the actual uncompressed data; it + * a big dictionary are not a problem in single-call mode. It is enough that + * the output buffer is big enough to hold the actual uncompressed data; it * can be smaller than the dictionary size stored in the stream headers. * + * Multi-call mode with preallocated dictionary (XZ_PREALLOC): dict_max bytes + * of memory is preallocated for the LZMA2 dictionary. This way there is no + * risk that xz_dec_run() could run out of memory, since xz_dec_run() will + * never allocate any memory. Instead, if the preallocated dictionary is too + * small for decoding the given input stream, xz_dec_run() will return + * XZ_MEMLIMIT_ERROR. Thus, it is important to know what kind of data will be + * decoded to avoid allocating excessive amount of memory for the dictionary. + * + * Multi-call mode with dynamically allocated dictionary (XZ_DYNALLOC): + * dict_max specifies the maximum allowed dictionary size that xz_dec_run() + * may allocate once it has parsed the dictionary size from the stream + * headers. This way excessive allocations can be avoided while still + * limiting the maximum memory usage to a sane value to prevent running the + * system out of memory when decompressing streams from untrusted sources. + * * On success, xz_dec_init() returns a pointer to struct xz_dec, which is - * ready to be used with xz_dec_run(). On error, xz_dec_init() returns NULL. + * ready to be used with xz_dec_run(). If memory allocation fails, + * xz_dec_init() returns NULL. */ -XZ_EXTERN struct xz_dec * XZ_FUNC xz_dec_init(uint32_t dict_max); +XZ_EXTERN struct xz_dec * XZ_FUNC xz_dec_init( + enum xz_mode mode, uint32_t dict_max); /** * xz_dec_run() - Run the XZ decoder * @s: Decoder state allocated using xz_dec_init() * @b: Input and output buffers * - * In multi-call mode, this function may return any of the values listed in - * enum xz_ret. - * - * In single-call mode, this function never returns XZ_OK. If an error occurs - * in single-call mode (return value is not XZ_STREAM_END), b->in_pos and - * b->out_pos are not modified, and the contents of the output buffer from - * b->out[b->out_pos] onward are undefined. - * - * NOTE: In single-call mode, the contents of the output buffer are undefined - * also after XZ_BUF_ERROR. This is because with some filter chains, there - * may be a second pass over the output buffer, and this pass cannot be - * properly done if the output buffer is truncated. Thus, you cannot give - * the single-call decoder a too small buffer and then expect to get that - * amount valid data from the beginning of the stream. You must use the - * multi-call decoder if you don't want to uncompress the whole stream. + * The possible return values depend on build options and operation mode. + * See enum xz_ret for details. + * + * NOTE: If an error occurs in single-call mode (return value is not + * XZ_STREAM_END), b->in_pos and b->out_pos are not modified, and the + * contents of the output buffer from b->out[b->out_pos] onward are + * undefined. This is true even after XZ_BUF_ERROR, because with some filter + * chains, there may be a second pass over the output buffer, and this pass + * cannot be properly done if the output buffer is truncated. Thus, you + * cannot give the single-call decoder a too small buffer and then expect to + * get that amount valid data from the beginning of the stream. You must use + * the multi-call decoder if you don't want to uncompress the whole stream. */ XZ_EXTERN enum xz_ret XZ_FUNC xz_dec_run(struct xz_dec *s, struct xz_buf *b); |