diff options
Diffstat (limited to 'include/sqfs/dir.h')
| -rw-r--r-- | include/sqfs/dir.h | 228 |
1 files changed, 228 insertions, 0 deletions
diff --git a/include/sqfs/dir.h b/include/sqfs/dir.h index 6bcb278..19c1289 100644 --- a/include/sqfs/dir.h +++ b/include/sqfs/dir.h @@ -22,26 +22,150 @@ #include "sqfs/predef.h" +/** + * @file dir.h + * + * @brief Contains on-disk data structures for the directory table and + * declarations for the @ref sqfs_dir_writer_t. + */ + +/** + * @struct sqfs_dir_writer_t + * + * @brief Abstracts generating of directory entries + * + * SquashFS stores directory entries and inodes seperated from each other. The + * inodes are stored in a series of meta data blocks before another series of + * meta data blocks that contain the directory entries. Directory inodes point + * to meta data block (and offset) where its contents are listed and the + * entries in turn point back to the inodes that represent them. + * + * There are some rules to this. Directory entries have to be written in + * ASCIIbetical ordering. Up to 256 entries are preceeded by a header. The + * entries use delta encoding for inode numbers and block locations relative to + * the header, so every time the inodes cross a meta data block boundary, if + * the difference in inode number gets too large, or if the entry count would + * exceed 256, a new header has to be emitted. Even if the inode pointed to is + * an extended type, the entry in the header still has to indicate the base + * type. + * + * In addtion to that, extended directory inodes can contain an index for + * faster lookup. The index points to each header and requires a new header to + * be emitted if the entries cross a block boundary. + * + * The dir writer takes care of all of this and provides a simple interface for + * adding entries. Internally it fills data into a meta data writer and + * generates an index that it can, on request, write to another meta data + * writer used for inodes. + */ + #define SQFS_MAX_DIR_ENT 256 +/** + * @struct sqfs_dir_header_t + * + * @brief On-disk data structure of a directory header + * + * See @ref sqfs_dir_writer_t for an overview on how SquashFS stores + * directories on disk. + */ struct sqfs_dir_header_t { + /** + * @brief The number of @ref sqfs_dir_entry_t entries that are + * following. + * + * This value is stored off by one and the total count must not + * exceed 256. + */ uint32_t count; + + /** + * @brief The location of the meta data block containing the inodes for + * the entries that follow, relative to the start of the inode + * table. + */ uint32_t start_block; + + /** + * @brief The inode number of the first entry. + */ uint32_t inode_number; }; +/** + * @struct sqfs_dir_entry_t + * + * @brief On-disk data structure of a directory entry. Many of these + * follow a single @ref sqfs_dir_header_t. + * + * See @ref sqfs_dir_writer_t for an overview on how SquashFS stores + * directories on disk. + */ struct sqfs_dir_entry_t { + /** + * @brief An offset into the uncompressed meta data block containing + * the coresponding inode. + */ uint16_t offset; + + /** + * @brief Signed difference of the inode number from the one + * in the @ref sqfs_dir_header_t. + */ int16_t inode_diff; + + /** + * @brief The @ref E_SQFS_INODE_TYPE value for the inode that this + * entry represents. + */ uint16_t type; + + /** + * @brief The size of the entry name + * + * This value is stored off-by-one. + */ uint16_t size; + + /** + * @brief The name of the directory entry (no trailing null-byte). + */ uint8_t name[]; }; +/** + * @struct sqfs_dir_index_t + * + * @brief On-disk data structure of a directory index. A series of those + * can follow an @ref sqfs_inode_dir_ext_t. + * + * See @ref sqfs_dir_writer_t for an overview on how SquashFS stores + * directories on disk. + */ struct sqfs_dir_index_t { + /** + * @brief Linear byte offset into the decompressed directory listing. + */ uint32_t index; + + /** + * @brief Location of the meta data block, relative to the directory + * table start. + */ uint32_t start_block; + + /** + * @brief Size of the name of the first entry after the header. + * + * This value is stored off-by-one. + */ uint32_t size; + + /** + * @brief Name of the name of the first entry after the header. + * + * No trailing null-byte. + */ uint8_t name[]; }; @@ -49,25 +173,129 @@ struct sqfs_dir_index_t { extern "C" { #endif +/** + * @brief Create a directory writer. + * + * @memberof sqfs_dir_writer_create + * + * @param dm A pointer to a meta data writer that the generated directory + * entries should be written to. + * + * @return A pointer to a directory writer on success, NULL on + * allocation failure. + */ SQFS_API sqfs_dir_writer_t *sqfs_dir_writer_create(sqfs_meta_writer_t *dm); +/** + * @brief Destroy a directory writer and free all its memory. + * + * @memberof sqfs_dir_writer_create + * + * @param writer A pointer to a directory writer object. + */ SQFS_API void sqfs_dir_writer_destroy(sqfs_dir_writer_t *writer); +/** + * @brief Begin writing a directory, i.e. reset and initialize all internal + * state neccessary. + * + * @memberof sqfs_dir_writer_create + * + * @param writer A pointer to a directory writer object. + * + * @return Zero on success, a @ref E_SQFS_ERROR value on failure. + */ SQFS_API int sqfs_dir_writer_begin(sqfs_dir_writer_t *writer); +/** + * @brief Add add a directory entry. + * + * @memberof sqfs_dir_writer_create + * + * @param writer A pointer to a directory writer object. + * @param name The name of the directory entry. + * @param inode_num The inode number of the entry. + * @param inode_ref A reference to the inode, i.e. the meta data block offset + * is stored in bits 16 to 48 and the lower 16 bit hold an + * offset into the block. + * @param mode A file mode, i.e. type and permission bits from which the entry + * type is derived internally. + * + * @return Zero on success, a @ref E_SQFS_ERROR value on failure. + */ SQFS_API int sqfs_dir_writer_add_entry(sqfs_dir_writer_t *writer, const char *name, uint32_t inode_num, uint64_t inode_ref, mode_t mode); +/** + * @brief Finish writing a directory listing and write everything out to the + * meta data writer. + * + * @memberof sqfs_dir_writer_create + * + * @param writer A pointer to a directory writer object. + * + * @return Zero on success, a @ref E_SQFS_ERROR value on failure. + */ SQFS_API int sqfs_dir_writer_end(sqfs_dir_writer_t *writer); +/** + * @brief Get the total, uncompressed size of the last written + * directory in bytes. + * + * @memberof sqfs_dir_writer_create + * + * Call this function after @ref sqfs_dir_writer_end to get the uncompressed + * size of the directory listing that is required for the directory inodes. + * And also to determine which kind of directory inode to create. + * + * @param writer A pointer to a directory writer object. + * + * @return The size of the entire, uncompressed listing in bytes. + */ SQFS_API size_t sqfs_dir_writer_get_size(sqfs_dir_writer_t *writer); +/** + * @brief Get the location of the last written directory. + * + * @memberof sqfs_dir_writer_create + * + * Call this function after @ref sqfs_dir_writer_end to get the location of + * the directory listing that is required for the directory inodes. + * + * @param writer A pointer to a directory writer object. + * + * @return A meta data reference, i.e. bits 16 to 48 contain the block start + * and the lower 16 bit an offset into the uncompressed block. + */ SQFS_API uint64_t sqfs_dir_writer_get_dir_reference(sqfs_dir_writer_t *writer); +/** + * @brief Get the size of the index of the last written directory. + * + * @memberof sqfs_dir_writer_create + * + * Call this function after @ref sqfs_dir_writer_end to get the size of + * the directory index that is required for extended directory inodes. + * + * @param writer A pointer to a directory writer object. + * + * @return The number of index entries. + */ SQFS_API size_t sqfs_dir_writer_get_index_size(sqfs_dir_writer_t *writer); +/** + * @brief Write the index of the index of the last written directory to + * a meta data writer after the extended directory inode. + * + * @memberof sqfs_dir_writer_create + * + * @param writer A pointer to a directory writer object. + * @param im A pointer to a meta data writer to write the index to. + * + * @return Zero on success, a @ref E_SQFS_ERROR value on failure. + */ SQFS_API int sqfs_dir_writer_write_index(sqfs_dir_writer_t *writer, sqfs_meta_writer_t *im); |