Cleanup: split "dir.h" into "dir_reader.h" and "dir_writer.h"

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 326 insertions, 0 deletions

diff --git a/include/sqfs/dir_reader.h b/include/sqfs/dir_reader.h
new file mode 100644
index 0000000..57b91e6
--- /dev/null
+++ b/include/sqfs/dir_reader.h
@@ -0,0 +1,326 @@
+/* SPDX-License-Identifier: LGPL-3.0-or-later */
+/*
+ * dir_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_DIR_READER_H
+#define SQFS_DIR_READER_H
+
+#include "sqfs/predef.h"
+
+/**
+ * @file dir_reader.h
+ *
+ * @brief Contains declarations for the @ref sqfs_dir_reader_t
+ */
+
+/**
+ * @struct sqfs_dir_reader_t
+ *
+ * @brief Abstracts reading of directory entries
+ *
+ * SquashFS stores directory listings and inode structures seperated from
+ * each other in meta data blocks.
+ *
+ * The sqfs_dir_reader_t abstracts access to the filesystem tree in a SquashFS
+ * through a fairly simple interface. It keeps two meta data readers internally
+ * for reading directory listings and inodes. Externally, it offers a few
+ * simple functions for iterating over the contents of a directory that
+ * completely take care of fetching/decoding headers and sifting through the
+ * multi level hierarchie used for storing them on disk.
+ *
+ * See @ref sqfs_dir_writer_t for an overview on how directory entries are
+ * stored in SquashFS.
+ *
+ * The reader also abstracts easy access to the underlying inodes, allowing
+ * direct access to the inode referred to by a directory entry.
+ */
+
+/**
+ * @enum E_SQFS_TREE_FILTER_FLAGS
+ *
+ * @brief Filter flags for @ref sqfs_dir_reader_get_full_hierarchy
+ */
+typedef enum {
+	/**
+	 * @brief Omit device special files from the final tree.
+	 */
+	SQFS_TREE_NO_DEVICES = 0x01,
+
+	/**
+	 * @brief Omit socket files from the final tree.
+	 */
+	SQFS_TREE_NO_SOCKETS = 0x02,
+
+	/**
+	 * @brief Omit named pipes from the final tree.
+	 */
+	SQFS_TREE_NO_FIFO = 0x04,
+
+	/**
+	 * @brief Omit symbolic links from the final tree.
+	 */
+	SQFS_TREE_NO_SLINKS = 0x08,
+
+	/**
+	 * @brief Omit empty directories from the final tree.
+	 *
+	 * If a directory is not empty on-disk, but ends up empty after
+	 * applying all the other filter rules, it is also omitted.
+	 */
+	SQFS_TREE_NO_EMPTY = 0x10,
+
+	/**
+	 * @brief Do not recurse into sub directories.
+	 *
+	 * If the start node is a directory, the tree deserializer will still
+	 * recurse into it, but it will not go beyond that.
+	 */
+	SQFS_TREE_NO_RECURSE = 0x20,
+
+	/**
+	 * @brief Store the list of parent nodes all the way to the target node
+	 *
+	 * When traversing towards the selected node, also collect the chain
+	 * of parent nodes with the subtree stored at the end.
+	 */
+	SQFS_TREE_STORE_PARENTS = 0x40,
+} E_SQFS_TREE_FILTER_FLAGS;
+
+/**
+ * @struct sqfs_tree_node_t
+ *
+ * @brief Encapsulates a node in the filesystem tree read by
+ *        @ref sqfs_dir_reader_get_full_hierarchy.
+ */
+struct sqfs_tree_node_t {
+	/**
+	 * @brief Pointer to parent, NULL for the root node
+	 */
+	sqfs_tree_node_t *parent;
+
+	/**
+	 * @brief For directories, a linked list of children.
+	 */
+	sqfs_tree_node_t *children;
+
+	/**
+	 * @brief Linked list next pointer for children list.
+	 */
+	sqfs_tree_node_t *next;
+
+	/**
+	 * @brief Inode representing this element in the tree.
+	 */
+	sqfs_inode_generic_t *inode;
+
+	/**
+	 * @brief Resolved 32 bit user ID from the inode
+	 */
+	uint32_t uid;
+
+	/**
+	 * @brief Resolved 32 bit group ID from the inode
+	 */
+	uint32_t gid;
+
+	/**
+	 * @brief null-terminated entry name.
+	 */
+	uint8_t name[];
+};
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Create a directory reader.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param super A pointer to the super block. Kept internally an used for
+ *              resolving table positions.
+ * @param cmp A compressor to use for unpacking meta data blocks.
+ * @param file The input file to read from.
+ *
+ * @return A new directory reader on success, NULL on allocation failure.
+ */
+SQFS_API sqfs_dir_reader_t *sqfs_dir_reader_create(const sqfs_super_t *super,
+						   sqfs_compressor_t *cmp,
+						   sqfs_file_t *file);
+
+/**
+ * @brief Cleanup a directory reader and free all its memory.
+ *
+ * @memberof sqfs_dir_reader_t
+ */
+SQFS_API void sqfs_dir_reader_destroy(sqfs_dir_reader_t *rd);
+
+/**
+ * @brief Navigate a directory reader to the location of a directory
+ *        represented by an inode.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * This function seeks to the meta data block containing the directory
+ * listing that the given inode referes to and resets the internal state.
+ * After that, consequtive cals to @ref sqfs_dir_reader_read can be made
+ * to iterate over the directory contents.
+ *
+ * @param rd A pointer to a directory reader.
+ * @param inode An directory or extended directory inode.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_open_dir(sqfs_dir_reader_t *rd,
+				      const sqfs_inode_generic_t *inode);
+
+/**
+ * @brief Reset a directory reader back to the beginning of the listing.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param rd A pointer to a directory reader.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_rewind(sqfs_dir_reader_t *rd);
+
+/**
+ * @brief Seek through the current directory listing to locate an
+ *        entry by name.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param rd A pointer to a directory reader.
+ * @param name The name of the entry to find.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_find(sqfs_dir_reader_t *rd, const char *name);
+
+/**
+ * @brief Read a directory entry and advance the internal position indicator
+ *        to the next one.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * Call this function repeatedly to iterate over a directory listing. It
+ * returns a positive number to indicate that it couldn't fetch any more data
+ * because the end of the listing was reached. A negative value indicates an
+ * error.
+ *
+ * After calling this function, you can use @ref sqfs_dir_reader_get_inode to
+ * read the full inode structure that the current entry referes to.
+ *
+ * @param rd A pointer to a directory reader.
+ * @param out Returns a pointer to a directory entry on success that can be
+ *            freed with a single free call.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure, a positive
+ *         number if the end of the current directory listing has been reached.
+ */
+SQFS_API int sqfs_dir_reader_read(sqfs_dir_reader_t *rd,
+				  sqfs_dir_entry_t **out);
+
+/**
+ * @brief Read the inode that the current directory entry points to.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param rd A pointer to a directory reader.
+ * @param out Returns a pointer to a generic inode that can be freed with a
+ *            single free call.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_get_inode(sqfs_dir_reader_t *rd,
+				       sqfs_inode_generic_t **inode);
+
+/**
+ * @brief Read the root inode using the location given by the super block.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param rd A pointer to a directory reader.
+ * @param out Returns a pointer to a generic inode that can be freed with a
+ *            single free call.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_get_root_inode(sqfs_dir_reader_t *rd,
+					    sqfs_inode_generic_t **inode);
+
+/**
+ * @brief Find an inode through path traversal from the root node downwards.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * @param rd A pointer to a directory reader.
+ * @param path A path to resolve into an inode. Forward or backward slashes can
+ *             be used to seperate path components. Resolving '.' or '..' is
+ *             not supported.
+ * @param out Returns a pointer to a generic inode that can be freed with a
+ *            single free call.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_find_by_path(sqfs_dir_reader_t *rd,
+					  const char *path,
+					  sqfs_inode_generic_t **out);
+
+/**
+ * @brief High level helper function for deserializing the entire file system
+ *        hierarchy into an in-memory tree structure.
+ *
+ * @memberof sqfs_dir_reader_t
+ *
+ * This function internally navigates to a specified inode using
+ * @ref sqfs_dir_reader_find_by_path and starting from that recursively
+ * deserializes the entire hierarchy into a tree structure holding all inodes.
+ *
+ * @param rd A pointer to a directory reader.
+ * @param path A path to resolve into an inode. Forward or backward slashes can
+ *             be used to seperate path components. Resolving '.' or '..' is
+ *             not supported. Can be set to NULL to get the root inode.
+ * @param flags A combination of @ref E_SQFS_TREE_FILTER_FLAGS flags.
+ * @param out Returns the top most tree node.
+ *
+ * @return Zero on success, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_dir_reader_get_full_hierarchy(sqfs_dir_reader_t *rd,
+						const sqfs_id_table_t *idtbl,
+						const char *path,
+						unsigned int flags,
+						sqfs_tree_node_t **out);
+
+/**
+ * @brief Recursively destroy a tree of @ref sqfs_tree_node_t nodes
+ *
+ * This function can be used to clean up after
+ * @ref sqfs_dir_reader_get_full_hierarchy.
+ *
+ * @param root A pointer to the root node.
+ */
+SQFS_API void sqfs_dir_tree_destroy(sqfs_tree_node_t *root);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SQFS_DIR_READER_H */