Comment on all the things

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

1 files changed, 240 insertions, 0 deletions

diff --git a/include/fstree.h b/include/fstree.h
index 5a8e422..f2ed67f 100644
--- a/include/fstree.h
+++ b/include/fstree.h
@@ -13,46 +13,197 @@ typedef struct file_info_t file_info_t;
 typedef struct dir_info_t dir_info_t;
 typedef struct fstree_t fstree_t;
 
+/**
+ * @struct file_info_t
+ *
+ * @brief Additional meta data stored in a @ref tree_node_t for regular files
+ */
 struct file_info_t {
 	char *input_file;
+
+	/**
+	 * @brief Linked list pointer for aggregating fragments
+	 *
+	 * When writing out data blocks, files that don't have a multiple of
+	 * the block size have their tail ends gathered in a fragment block.
+	 * A linked list is used to keep track of which files share the same
+	 * fragment block.
+	 */
 	file_info_t *frag_next;
+
+	/**
+	 * @brief Total size of the file in bytes
+	 */
 	uint64_t size;
+
+	/**
+	 * @brief Absolute position of the first data block
+	 */
 	uint64_t startblock;
+
+	/**
+	 * @brief Fragment index
+	 *
+	 * If the size is not a multiple of the block size, this holds an
+	 * index into the fragment table.
+	 */
 	uint32_t fragment;
+
+	/**
+	 * @brief Byte offset into the fragment block
+	 *
+	 * If the size is not a multiple of the block size, this holds an
+	 * offset into the fragment block.
+	 */
 	uint32_t fragment_offset;
+
+	/**
+	 * @brief Stores the compressed file block sizes
+	 *
+	 * For each full data block, stores the compressed size. Bit number
+	 * 24 is set if the block is stored uncompressed.
+	 */
 	uint32_t blocksizes[];
 };
 
+/**
+ * @struct dir_info_t
+ *
+ * @brief Additional meta data stored in a @ref tree_node_t for directories
+ */
 struct dir_info_t {
+	/**
+	 * @brief Pointer to the head of the linked list of children
+	 */
 	tree_node_t *children;
+
+	/**
+	 * @brief Size of the directory
+	 *
+	 * Computed and updated on the fly while writing directory
+	 * meta data to disk.
+	 */
 	uint64_t size;
+
+	/**
+	 * @brief Start block offset, relative to directory table start
+	 *
+	 * Offset of the compressed meta data block where the directory
+	 * listing is stored in the SquashFS image.
+	 */
 	uint64_t start_block;
+
+	/**
+	 * @brief Byte offset into the uncompressed meta data block
+	 *
+	 * Points at where in the meta data block the directory listing begins.
+	 */
 	uint32_t block_offset;
+
+	/**
+	 * @brief Set to true for implicitly generated directories
+	 */
 	bool created_implicitly;
 };
 
+/**
+ * @struct tree_node_t
+ *
+ * @brief A node in a file system tree
+ */
 struct tree_node_t {
+	/**
+	 * @brief Linked list pointer to the next node in the same directory
+	 */
 	tree_node_t *next;
+
+	/**
+	 * @brief Pointer to directory node that this node is in
+	 *
+	 * This is NULL only for the root node
+	 */
 	tree_node_t *parent;
+
+	/**
+	 * @brief Pointer into the payload area where the node name is stored
+	 *
+	 * For the root node, this points to an empty string
+	 */
 	char *name;
+
 	uint32_t uid;
 	uint32_t gid;
 	uint16_t mode;
 
+	/**
+	 * @brief SquashFS inode refernce number
+	 *
+	 * This is computed and stored here on the fly when writing inodes
+	 * generated from tree nodes to the SquashFS image.
+	 *
+	 * An inode reference is the 32 bit offset of the compressed meta data
+	 * block, shifted left by 16 and ored with a 13 bit offset into the
+	 * uncompressed meta data block.
+	 */
 	uint64_t inode_ref;
+
+	/**
+	 * @brief inode number
+	 *
+	 * This is computed and stored here on the fly when writing inodes
+	 * generated from tree nodes to the SquashFS image.
+	 */
 	uint32_t inode_num;
+
+	/**
+	 * @brief SquashFS inode type used for this tree node
+	 *
+	 * This is computed and stored here on the fly when writing inodes
+	 * generated from tree nodes to the SquashFS image. It can't be
+	 * easily determined in advance since it depends also on the size
+	 * of the node, which means for directories the size of the directory
+	 * entries once written to disk.
+	 *
+	 * All code that actually processes tree nodes should use the mode
+	 * field instead (mode & S_IFMT gives us the node type). It is stored
+	 * here when generating inodes since we need it later on to generate
+	 * directory entries.
+	 */
 	int type;
 
 	union {
+		/**
+		 * @brief Pointer into payload area storing directory meta data
+		 */
 		dir_info_t *dir;
+
+		/**
+		 * @brief Pointer into payload area storing file meta data
+		 */
 		file_info_t *file;
+
+		/**
+		 * @brief Pointer into payload area storing symlink target
+		 */
 		char *slink_target;
+
+		/**
+		 * @brief A device number for device special files
+		 */
 		uint64_t devno;
 	} data;
 
+	/**
+	 * @brief Additional data stored in the tree node
+	 */
 	uint8_t payload[];
 };
 
+/**
+ * @struct fstree_t
+ *
+ * @brief Encapsulates a file system tree
+ */
 struct fstree_t {
 	uint32_t default_uid;
 	uint32_t default_gid;
@@ -63,21 +214,110 @@ struct fstree_t {
 	tree_node_t *root;
 };
 
+/**
+ * @brief Initialize an fstree object
+ *
+ * @memberof fstree_t
+ *
+ * Initializing means copying over the default values and creating a root node.
+ * On error, an error message is written to stderr.
+ *
+ * @param fs           A pointer to an uninitialized fstree object
+ * @param block_size   The data block size for regular files
+ * @param mtime        Default modification time stamp to use on all nodes
+ * @param default_mode Default permission bits to use on implicitly created
+ *                     directories.
+ * @param default_uid  Default UID to set on implicitly created directories.
+ * @param default_gid  Default GID to set on implicitly created directories.
+ *
+ * @return Zero on success, -1 on failure
+ */
 int fstree_init(fstree_t *fs, size_t block_size, uint32_t mtime,
 		uint16_t default_mode, uint32_t default_uid,
 		uint32_t default_gid);
 
+/**
+ * @brief Clean up an fstree object and free all memory it uses
+ *
+ * @memberof fstree_t
+ *
+ * This function also recursively frees all tree nodes.
+ *
+ * @param fs A pointer to an fstree object
+ */
 void fstree_cleanup(fstree_t *fs);
 
+/**
+ * @brief Add a generic node to an fstree object
+ *
+ * @memberof fstree_t
+ *
+ * The new node is inserted by path. If some components of the path don't
+ * exist, they are created as directories with default permissions, like
+ * mkdir -p would, and marked as implcitily created. A subsequent call that
+ * tries to create an existing tree node will fail, except if the target
+ * is an implicitly created directory node and the call tries to create it
+ * as a directory. This will simply overwrite the permissions and ownership.
+ * The implicitly created flag is then cleared and subsequent attempts to
+ * create this directory again will also fail.
+ *
+ * This function does not print anything to stderr, instead it sets an
+ * appropriate errno value.
+ *
+ * @param fs        A pointer to an fstree object
+ * @param path      The path of the new object to insert
+ * @param mode      Specifies both access permission and what kind of node
+ *                  to create
+ * @param uid       The user id that owns the new node
+ * @param gid       The group id that owns the new node
+ * @param extra_len An additional number of bytes to allocate for payload data
+ *
+ * @return A pointer to the new tree node or NULL on failure
+ */
 tree_node_t *fstree_add(fstree_t *fs, const char *path, uint16_t mode,
 			uint32_t uid, uint32_t gid, size_t extra_len);
 
+/**
+ * @brief A wrappter around @ref fstree_add for regular files
+ *
+ * @memberof fstree_t
+ *
+ * This function internally computes the number of extra payload bytes
+ * requiered and sets up the payload pointers propperly, as they are
+ * different than for other types of nodes.
+ *
+ * @return A pointer to the new tree node or NULL on failure
+ */
 tree_node_t *fstree_add_file(fstree_t *fs, const char *path, uint16_t mode,
 			     uint32_t uid, uint32_t gid, uint64_t filesz,
 			     const char *input);
 
+/**
+ * @brief Load an fstree from a text file describing it
+ *
+ * @memberof fstree_t
+ *
+ * This function parses the file format accepted by gensquashfs and restores
+ * a file system tree from it.
+ *
+ * On failure, an error report with filename and line number is written
+ * to stderr.
+ *
+ * @param fs       A pointer to an fstree object that is already initialized
+ *                 prior to calling this function.
+ * @param filename The path to the input file to process.
+ *
+ * @return Zero on success, -1 on failure.
+ */
 int fstree_from_file(fstree_t *fs, const char *filename);
 
+/**
+ * @brief Lexicographically sort all directory contents
+ *
+ * @memberof fstree_t
+ *
+ * @param fs A pointer to an fstree object
+ */
 void fstree_sort(fstree_t *fs);
 
 #endif /* FSTREE_H */