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/* SPDX-License-Identifier: LGPL-3.0-or-later */
/*
* meta_reader.h - This file is part of libsquashfs
*
* Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#ifndef SQFS_META_READER_H
#define SQFS_META_READER_H
#include "sqfs/predef.h"
/**
* @file meta_reader.h
*
* @brief Contains declarations for the @ref sqfs_meta_reader_t.
*/
/**
* @struct sqfs_meta_reader_t
*
* @implements sqfs_object_t
*
* @brief Abstracts reading of meta data blocks.
*
* SquashFS stores meta data by dividing it into fixed size (8k) chunks
* that are written to disk with a small header indicating the on-disk
* size and whether it is compressed or not.
*
* Data written to meta data blocks doesn't have to be aligned, i.e.
* SquashFS doesn't care if an object is written across two blocks.
*
* The main task of the meta data read is to provide a simple read and seek
* functions that transparently take care of fetching and uncompressing blocks
* from disk and reading transparently across block boarders if required.
*/
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Create a meta data reader
*
* @memberof sqfs_meta_reader_t
*
* @param file A pointer to a file object to read from
* @param cmp A compressor to use for unpacking compressed meta data blocks
* @param start A lower limit for the blocks to be read. Every seek to an offset
* below that is interpreted as an out-of-bounds read.
* @param limit An upper limit for the blocks to read. Every seek to an offset
* afer that is interpreted as an out-of-bounds read.
*
* @return A pointer to a meta data reader on success, NULL on
* allocation failure.
*/
SQFS_API sqfs_meta_reader_t *sqfs_meta_reader_create(sqfs_file_t *file,
sqfs_compressor_t *cmp,
sqfs_u64 start,
sqfs_u64 limit);
/**
* @brief Seek to a specific meta data block and offset.
*
* @memberof sqfs_meta_reader_t
*
* The underlying block is fetched from disk and uncompressed, unless it
* already is the current block.
*
* @param m A pointer to a meta data reader.
* @param block_start Absolute position where the block header can be found.
* @param offset A byte offset into the uncompressed block.
*
* @return Zero on success, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_meta_reader_seek(sqfs_meta_reader_t *m, sqfs_u64 block_start,
size_t offset);
/**
* @brief Get the current position that the next read will read from.
*
* @memberof sqfs_meta_reader_t
*
* @param m A pointer to a meta data reader.
* @param block_start Absolute position where the current block is.
* @param offset A byte offset into the uncompressed block.
*/
SQFS_API void sqfs_meta_reader_get_position(const sqfs_meta_reader_t *m,
sqfs_u64 *block_start,
size_t *offset);
/**
* @brief Read a chunk of data from a meta data reader.
*
* @memberof sqfs_meta_reader_t
*
* If the meta data reader reaches the end of the current block before filling
* the destination buffer, it transparently reads the next block from disk and
* uncompresses it.
*
* @param m A pointer to a meta data reader.
* @param data A pointer to copy the data to.
* @param size The numbre of bytes to read.
*
* @return Zero on success, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_meta_reader_read(sqfs_meta_reader_t *m, void *data,
size_t size);
/**
* @brief Read and decode a directory header from a meta data reader.
*
* @memberof sqfs_meta_reader_t
*
* This is a convenience function on to of @ref sqfs_meta_reader_read that
* reads and decodes a directory header from a meta data block.
*
* @param m A pointer to a meta data reader.
* @param hdr A pointer to a directory header to fill.
*
* @return Zero on success, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_meta_reader_read_dir_header(sqfs_meta_reader_t *m,
sqfs_dir_header_t *hdr);
/**
* @brief Read and decode a directory header from a meta data reader.
*
* @memberof sqfs_meta_reader_t
*
* This is a convenience function on to of @ref sqfs_meta_reader_read that
* reads and decodes a directory entry.
*
* @param m A pointer to a meta data reader.
* @param ent Returns a pointer to a directory entry. Can be released with a
* single @ref sqfs_free call.
*
* @return Zero on success, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_meta_reader_read_dir_ent(sqfs_meta_reader_t *m,
sqfs_dir_entry_t **ent);
/**
* @brief Read and decode an inode from a meta data reader.
*
* @memberof sqfs_meta_reader_t
*
* This is a convenience function on to of @ref sqfs_meta_reader_seek and
* @ref sqfs_meta_reader_read that reads and decodes an inode.
*
* @param ir A pointer to a meta data reader.
* @param super A pointer to the super block, required for figuring out the
* size of file inodes.
* @param block_start The meta data block to seek to for reading the inode.
* @param offset A byte offset within the uncompressed block where the
* inode is.
* @param out Returns a pointer to an inode. Can be released with a
* single @ref sqfs_free call.
*
* @return Zero on success, an @ref SQFS_ERROR value on failure.
*/
SQFS_API
int sqfs_meta_reader_read_inode(sqfs_meta_reader_t *ir,
const sqfs_super_t *super,
sqfs_u64 block_start, size_t offset,
sqfs_inode_generic_t **out);
#ifdef __cplusplus
}
#endif
#endif /* SQFS_META_READER_H */
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