--- /dev/null
+/* SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause */
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of https://github.com/facebook/zstd) and
+ * the GPLv2 (found in the COPYING file in the root directory of
+ * https://github.com/facebook/zstd). You may select, at your option, one of the
+ * above-listed licenses.
+ */
+
+#ifndef LINUX_ZSTD_H
+#define LINUX_ZSTD_H
+
+/**
+ * This is a kernel-style API that wraps the upstream zstd API, which cannot be
+ * used directly because the symbols aren't exported. It exposes the minimal
+ * functionality which is currently required by users of zstd in the kernel.
+ * Expose extra functions from lib/zstd/zstd.h as needed.
+ */
+
+/* ====== Dependency ====== */
+#include <linux/types.h>
+#include <linux/zstd_errors.h>
+#include <linux/zstd_lib.h>
+
+/* ====== Helper Functions ====== */
+/**
+ * zstd_compress_bound() - maximum compressed size in worst case scenario
+ * @src_size: The size of the data to compress.
+ *
+ * Return: The maximum compressed size in the worst case scenario.
+ */
+size_t zstd_compress_bound(size_t src_size);
+
+/**
+ * zstd_is_error() - tells if a size_t function result is an error code
+ * @code: The function result to check for error.
+ *
+ * Return: Non-zero iff the code is an error.
+ */
+unsigned int zstd_is_error(size_t code);
+
+/**
+ * enum zstd_error_code - zstd error codes
+ */
+typedef ZSTD_ErrorCode zstd_error_code;
+
+/**
+ * zstd_get_error_code() - translates an error function result to an error code
+ * @code: The function result for which zstd_is_error(code) is true.
+ *
+ * Return: A unique error code for this error.
+ */
+zstd_error_code zstd_get_error_code(size_t code);
+
+/**
+ * zstd_get_error_name() - translates an error function result to a string
+ * @code: The function result for which zstd_is_error(code) is true.
+ *
+ * Return: An error string corresponding to the error code.
+ */
+const char *zstd_get_error_name(size_t code);
+
+/**
+ * zstd_min_clevel() - minimum allowed compression level
+ *
+ * Return: The minimum allowed compression level.
+ */
+int zstd_min_clevel(void);
+
+/**
+ * zstd_max_clevel() - maximum allowed compression level
+ *
+ * Return: The maximum allowed compression level.
+ */
+int zstd_max_clevel(void);
+
+/* ====== Parameter Selection ====== */
+
+/**
+ * enum zstd_strategy - zstd compression search strategy
+ *
+ * From faster to stronger. See zstd_lib.h.
+ */
+typedef ZSTD_strategy zstd_strategy;
+
+/**
+ * struct zstd_compression_parameters - zstd compression parameters
+ * @windowLog: Log of the largest match distance. Larger means more
+ * compression, and more memory needed during decompression.
+ * @chainLog: Fully searched segment. Larger means more compression,
+ * slower, and more memory (useless for fast).
+ * @hashLog: Dispatch table. Larger means more compression,
+ * slower, and more memory.
+ * @searchLog: Number of searches. Larger means more compression and slower.
+ * @searchLength: Match length searched. Larger means faster decompression,
+ * sometimes less compression.
+ * @targetLength: Acceptable match size for optimal parser (only). Larger means
+ * more compression, and slower.
+ * @strategy: The zstd compression strategy.
+ *
+ * See zstd_lib.h.
+ */
+typedef ZSTD_compressionParameters zstd_compression_parameters;
+
+/**
+ * struct zstd_frame_parameters - zstd frame parameters
+ * @contentSizeFlag: Controls whether content size will be present in the
+ * frame header (when known).
+ * @checksumFlag: Controls whether a 32-bit checksum is generated at the
+ * end of the frame for error detection.
+ * @noDictIDFlag: Controls whether dictID will be saved into the frame
+ * header when using dictionary compression.
+ *
+ * The default value is all fields set to 0. See zstd_lib.h.
+ */
+typedef ZSTD_frameParameters zstd_frame_parameters;
+
+/**
+ * struct zstd_parameters - zstd parameters
+ * @cParams: The compression parameters.
+ * @fParams: The frame parameters.
+ */
+typedef ZSTD_parameters zstd_parameters;
+
+/**
+ * zstd_get_params() - returns zstd_parameters for selected level
+ * @level: The compression level
+ * @estimated_src_size: The estimated source size to compress or 0
+ * if unknown.
+ *
+ * Return: The selected zstd_parameters.
+ */
+zstd_parameters zstd_get_params(int level,
+ unsigned long long estimated_src_size);
+
+/* ====== Single-pass Compression ====== */
+
+typedef ZSTD_CCtx zstd_cctx;
+
+/**
+ * zstd_cctx_workspace_bound() - max memory needed to initialize a zstd_cctx
+ * @parameters: The compression parameters to be used.
+ *
+ * If multiple compression parameters might be used, the caller must call
+ * zstd_cctx_workspace_bound() for each set of parameters and use the maximum
+ * size.
+ *
+ * Return: A lower bound on the size of the workspace that is passed to
+ * zstd_init_cctx().
+ */
+size_t zstd_cctx_workspace_bound(const zstd_compression_parameters *parameters);
+
+/**
+ * zstd_init_cctx() - initialize a zstd compression context
+ * @workspace: The workspace to emplace the context into. It must outlive
+ * the returned context.
+ * @workspace_size: The size of workspace. Use zstd_cctx_workspace_bound() to
+ * determine how large the workspace must be.
+ *
+ * Return: A zstd compression context or NULL on error.
+ */
+zstd_cctx *zstd_init_cctx(void *workspace, size_t workspace_size);
+
+/**
+ * zstd_compress_cctx() - compress src into dst with the initialized parameters
+ * @cctx: The context. Must have been initialized with zstd_init_cctx().
+ * @dst: The buffer to compress src into.
+ * @dst_capacity: The size of the destination buffer. May be any size, but
+ * ZSTD_compressBound(srcSize) is guaranteed to be large enough.
+ * @src: The data to compress.
+ * @src_size: The size of the data to compress.
+ * @parameters: The compression parameters to be used.
+ *
+ * Return: The compressed size or an error, which can be checked using
+ * zstd_is_error().
+ */
+size_t zstd_compress_cctx(zstd_cctx *cctx, void *dst, size_t dst_capacity,
+ const void *src, size_t src_size, const zstd_parameters *parameters);
+
+/* ====== Single-pass Decompression ====== */
+
+typedef ZSTD_DCtx zstd_dctx;
+
+/**
+ * zstd_dctx_workspace_bound() - max memory needed to initialize a zstd_dctx
+ *
+ * Return: A lower bound on the size of the workspace that is passed to
+ * zstd_init_dctx().
+ */
+size_t zstd_dctx_workspace_bound(void);
+
+/**
+ * zstd_init_dctx() - initialize a zstd decompression context
+ * @workspace: The workspace to emplace the context into. It must outlive
+ * the returned context.
+ * @workspace_size: The size of workspace. Use zstd_dctx_workspace_bound() to
+ * determine how large the workspace must be.
+ *
+ * Return: A zstd decompression context or NULL on error.
+ */
+zstd_dctx *zstd_init_dctx(void *workspace, size_t workspace_size);
+
+/**
+ * zstd_decompress_dctx() - decompress zstd compressed src into dst
+ * @dctx: The decompression context.
+ * @dst: The buffer to decompress src into.
+ * @dst_capacity: The size of the destination buffer. Must be at least as large
+ * as the decompressed size. If the caller cannot upper bound the
+ * decompressed size, then it's better to use the streaming API.
+ * @src: The zstd compressed data to decompress. Multiple concatenated
+ * frames and skippable frames are allowed.
+ * @src_size: The exact size of the data to decompress.
+ *
+ * Return: The decompressed size or an error, which can be checked using
+ * zstd_is_error().
+ */
+size_t zstd_decompress_dctx(zstd_dctx *dctx, void *dst, size_t dst_capacity,
+ const void *src, size_t src_size);
+
+/* ====== Streaming Buffers ====== */
+
+/**
+ * struct zstd_in_buffer - input buffer for streaming
+ * @src: Start of the input buffer.
+ * @size: Size of the input buffer.
+ * @pos: Position where reading stopped. Will be updated.
+ * Necessarily 0 <= pos <= size.
+ *
+ * See zstd_lib.h.
+ */
+typedef ZSTD_inBuffer zstd_in_buffer;
+
+/**
+ * struct zstd_out_buffer - output buffer for streaming
+ * @dst: Start of the output buffer.
+ * @size: Size of the output buffer.
+ * @pos: Position where writing stopped. Will be updated.
+ * Necessarily 0 <= pos <= size.
+ *
+ * See zstd_lib.h.
+ */
+typedef ZSTD_outBuffer zstd_out_buffer;
+
+/* ====== Streaming Compression ====== */
+
+typedef ZSTD_CStream zstd_cstream;
+
+/**
+ * zstd_cstream_workspace_bound() - memory needed to initialize a zstd_cstream
+ * @cparams: The compression parameters to be used for compression.
+ *
+ * Return: A lower bound on the size of the workspace that is passed to
+ * zstd_init_cstream().
+ */
+size_t zstd_cstream_workspace_bound(const zstd_compression_parameters *cparams);
+
+/**
+ * zstd_init_cstream() - initialize a zstd streaming compression context
+ * @parameters The zstd parameters to use for compression.
+ * @pledged_src_size: If params.fParams.contentSizeFlag == 1 then the caller
+ * must pass the source size (zero means empty source).
+ * Otherwise, the caller may optionally pass the source
+ * size, or zero if unknown.
+ * @workspace: The workspace to emplace the context into. It must outlive
+ * the returned context.
+ * @workspace_size: The size of workspace.
+ * Use zstd_cstream_workspace_bound(params->cparams) to
+ * determine how large the workspace must be.
+ *
+ * Return: The zstd streaming compression context or NULL on error.
+ */
+zstd_cstream *zstd_init_cstream(const zstd_parameters *parameters,
+ unsigned long long pledged_src_size, void *workspace, size_t workspace_size);
+
+/**
+ * zstd_reset_cstream() - reset the context using parameters from creation
+ * @cstream: The zstd streaming compression context to reset.
+ * @pledged_src_size: Optionally the source size, or zero if unknown.
+ *
+ * Resets the context using the parameters from creation. Skips dictionary
+ * loading, since it can be reused. If `pledged_src_size` is non-zero the frame
+ * content size is always written into the frame header.
+ *
+ * Return: Zero or an error, which can be checked using
+ * zstd_is_error().
+ */
+size_t zstd_reset_cstream(zstd_cstream *cstream,
+ unsigned long long pledged_src_size);
+
+/**
+ * zstd_compress_stream() - streaming compress some of input into output
+ * @cstream: The zstd streaming compression context.
+ * @output: Destination buffer. `output->pos` is updated to indicate how much
+ * compressed data was written.
+ * @input: Source buffer. `input->pos` is updated to indicate how much data
+ * was read. Note that it may not consume the entire input, in which
+ * case `input->pos < input->size`, and it's up to the caller to
+ * present remaining data again.
+ *
+ * The `input` and `output` buffers may be any size. Guaranteed to make some
+ * forward progress if `input` and `output` are not empty.
+ *
+ * Return: A hint for the number of bytes to use as the input for the next
+ * function call or an error, which can be checked using
+ * zstd_is_error().
+ */
+size_t zstd_compress_stream(zstd_cstream *cstream, zstd_out_buffer *output,
+ zstd_in_buffer *input);
+
+/**
+ * zstd_flush_stream() - flush internal buffers into output
+ * @cstream: The zstd streaming compression context.
+ * @output: Destination buffer. `output->pos` is updated to indicate how much
+ * compressed data was written.
+ *
+ * zstd_flush_stream() must be called until it returns 0, meaning all the data
+ * has been flushed. Since zstd_flush_stream() causes a block to be ended,
+ * calling it too often will degrade the compression ratio.
+ *
+ * Return: The number of bytes still present within internal buffers or an
+ * error, which can be checked using zstd_is_error().
+ */
+size_t zstd_flush_stream(zstd_cstream *cstream, zstd_out_buffer *output);
+
+/**
+ * zstd_end_stream() - flush internal buffers into output and end the frame
+ * @cstream: The zstd streaming compression context.
+ * @output: Destination buffer. `output->pos` is updated to indicate how much
+ * compressed data was written.
+ *
+ * zstd_end_stream() must be called until it returns 0, meaning all the data has
+ * been flushed and the frame epilogue has been written.
+ *
+ * Return: The number of bytes still present within internal buffers or an
+ * error, which can be checked using zstd_is_error().
+ */
+size_t zstd_end_stream(zstd_cstream *cstream, zstd_out_buffer *output);
+
+/* ====== Streaming Decompression ====== */
+
+typedef ZSTD_DStream zstd_dstream;
+
+/**
+ * zstd_dstream_workspace_bound() - memory needed to initialize a zstd_dstream
+ * @max_window_size: The maximum window size allowed for compressed frames.
+ *
+ * Return: A lower bound on the size of the workspace that is passed
+ * to zstd_init_dstream().
+ */
+size_t zstd_dstream_workspace_bound(size_t max_window_size);
+
+/**
+ * zstd_init_dstream() - initialize a zstd streaming decompression context
+ * @max_window_size: The maximum window size allowed for compressed frames.
+ * @workspace: The workspace to emplace the context into. It must outlive
+ * the returned context.
+ * @workspaceSize: The size of workspace.
+ * Use zstd_dstream_workspace_bound(max_window_size) to
+ * determine how large the workspace must be.
+ *
+ * Return: The zstd streaming decompression context.
+ */
+zstd_dstream *zstd_init_dstream(size_t max_window_size, void *workspace,
+ size_t workspace_size);
+
+/**
+ * zstd_reset_dstream() - reset the context using parameters from creation
+ * @dstream: The zstd streaming decompression context to reset.
+ *
+ * Resets the context using the parameters from creation. Skips dictionary
+ * loading, since it can be reused.
+ *
+ * Return: Zero or an error, which can be checked using zstd_is_error().
+ */
+size_t zstd_reset_dstream(zstd_dstream *dstream);
+
+/**
+ * zstd_decompress_stream() - streaming decompress some of input into output
+ * @dstream: The zstd streaming decompression context.
+ * @output: Destination buffer. `output.pos` is updated to indicate how much
+ * decompressed data was written.
+ * @input: Source buffer. `input.pos` is updated to indicate how much data was
+ * read. Note that it may not consume the entire input, in which case
+ * `input.pos < input.size`, and it's up to the caller to present
+ * remaining data again.
+ *
+ * The `input` and `output` buffers may be any size. Guaranteed to make some
+ * forward progress if `input` and `output` are not empty.
+ * zstd_decompress_stream() will not consume the last byte of the frame until
+ * the entire frame is flushed.
+ *
+ * Return: Returns 0 iff a frame is completely decoded and fully flushed.
+ * Otherwise returns a hint for the number of bytes to use as the
+ * input for the next function call or an error, which can be checked
+ * using zstd_is_error(). The size hint will never load more than the
+ * frame.
+ */
+size_t zstd_decompress_stream(zstd_dstream *dstream, zstd_out_buffer *output,
+ zstd_in_buffer *input);
+
+/* ====== Frame Inspection Functions ====== */
+
+/**
+ * zstd_find_frame_compressed_size() - returns the size of a compressed frame
+ * @src: Source buffer. It should point to the start of a zstd encoded
+ * frame or a skippable frame.
+ * @src_size: The size of the source buffer. It must be at least as large as the
+ * size of the frame.
+ *
+ * Return: The compressed size of the frame pointed to by `src` or an error,
+ * which can be check with zstd_is_error().
+ * Suitable to pass to ZSTD_decompress() or similar functions.
+ */
+size_t zstd_find_frame_compressed_size(const void *src, size_t src_size);
+
+/**
+ * struct zstd_frame_params - zstd frame parameters stored in the frame header
+ * @frameContentSize: The frame content size, or ZSTD_CONTENTSIZE_UNKNOWN if not
+ * present.
+ * @windowSize: The window size, or 0 if the frame is a skippable frame.
+ * @blockSizeMax: The maximum block size.
+ * @frameType: The frame type (zstd or skippable)
+ * @headerSize: The size of the frame header.
+ * @dictID: The dictionary id, or 0 if not present.
+ * @checksumFlag: Whether a checksum was used.
+ *
+ * See zstd_lib.h.
+ */
+typedef ZSTD_frameHeader zstd_frame_header;
+
+/**
+ * zstd_get_frame_header() - extracts parameters from a zstd or skippable frame
+ * @params: On success the frame parameters are written here.
+ * @src: The source buffer. It must point to a zstd or skippable frame.
+ * @src_size: The size of the source buffer.
+ *
+ * Return: 0 on success. If more data is required it returns how many bytes
+ * must be provided to make forward progress. Otherwise it returns
+ * an error, which can be checked using zstd_is_error().
+ */
+size_t zstd_get_frame_header(zstd_frame_header *params, const void *src,
+ size_t src_size);
+
+#endif /* LINUX_ZSTD_H */
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