lib/fs/ext2/dir.c

/*
 * Copyright (c) 2007 Travis Geiselbrecht
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Software,
 * and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
#include <string.h>
#include <stdlib.h>
#include <debug.h>
#include <err.h>
#include <lib/fs/ext2.h>
#include "ext2_priv.h"

#define LOCAL_TRACE 0

/* read in the dir, look for the entry */
static int ext2_dir_lookup(ext2_t *ext2, struct ext2_inode *dir_inode, const char *name, inodenum_t *inum)
{
	uint file_blocknum;
	int err;
	uint8_t *buf;
	size_t namelen = strlen(name);
	
	if (!S_ISDIR(dir_inode->i_mode))
		return ERR_NOT_DIR;

	buf = malloc(EXT2_BLOCK_SIZE(ext2->sb));

	file_blocknum = 0;
	for (;;) {
		/* read in the offset */
		err = ext2_read_inode(ext2, dir_inode, buf, file_blocknum * EXT2_BLOCK_SIZE(ext2->sb), EXT2_BLOCK_SIZE(ext2->sb));
		if (err <= 0) {
			free(buf);
			return -1;
		}

		/* walk through the directory entries, looking for the one that matches */
		struct ext2_dir_entry_2 *ent;
		uint pos = 0;
		while (pos < EXT2_BLOCK_SIZE(ext2->sb)) {
			ent = (struct ext2_dir_entry_2 *)&buf[pos];

			LTRACEF("ent %d:%d: inode 0x%x, reclen %d, namelen %d\n",
					file_blocknum, pos, LE32(ent->inode), LE16(ent->rec_len), ent->name_len/* , ent->name*/);

			/* sanity check the record length */
			if (LE16(ent->rec_len) == 0)
				break;

			if (ent->name_len == namelen && memcmp(name, ent->name, ent->name_len) == 0) {
				// match
				*inum = LE32(ent->inode);
				LTRACEF("match: inode %d\n", *inum);
				free(buf);
				return 1;
			}

			pos += ROUNDUP(LE16(ent->rec_len), 4);
		}

		file_blocknum++;

		/* sanity check the directory. 4MB should be enough */
		if (file_blocknum > 1024) {
			free(buf);
			return -1;
		}
	}
}

/* note, trashes path */
static int ext2_walk(ext2_t *ext2, char *path, struct ext2_inode *start_inode, inodenum_t *inum, int recurse)
{
	char *ptr;
	struct ext2_inode inode;
	struct ext2_inode dir_inode;
	int err;
	bool done;

	LTRACEF("path '%s', start_inode %p, inum %p, recurse %d\n", path, start_inode, inum, recurse);

	if (recurse > 4)
		return ERR_RECURSE_TOO_DEEP;

	/* chew up leading slashes */
	ptr = &path[0];
	while (*ptr == '/')
		ptr++;

	done = false;
	memcpy(&dir_inode, start_inode, sizeof(struct ext2_inode));
	while (!done) {
		/* process the first component */
		char *next_sep = strchr(ptr, '/');
		if (next_sep) {
			/* terminate the next component, giving us a substring */
			*next_sep = 0;
		} else {
			/* this is the last component */
			done = true;
		}

		LTRACEF("component '%s', done %d\n", ptr, done);

		/* do the lookup on this component */
		err = ext2_dir_lookup(ext2, &dir_inode, ptr, inum);
		if (err < 0)
			return err;

nextcomponent:
		LTRACEF("inum %u\n", *inum);

		/* load the next inode */
		err = ext2_load_inode(ext2, *inum, &inode);
		if (err < 0)
			return err;
		
		/* is it a symlink? */
		if (S_ISLNK(inode.i_mode)) {
			char link[512];

			LTRACEF("hit symlink\n");

			err = ext2_read_link(ext2, &inode, link, sizeof(link));
			if (err < 0)
				return err;

			LTRACEF("symlink read returns %d '%s'\n", err, link);

			/* recurse, parsing the link */
			if (link[0] == '/') {
				/* link starts with '/', so start over again at the rootfs */
				err = ext2_walk(ext2, link, &ext2->root_inode, inum, recurse + 1);
			} else {
				err = ext2_walk(ext2, link, &dir_inode, inum, recurse + 1);
			}

			LTRACEF("recursive walk returns %d\n", err);

			if (err < 0)
				return err;

			/* if we weren't done with our path parsing, start again with the result of this recurse */
			if (!done) {
				goto nextcomponent;
			}
		} else if (S_ISDIR(inode.i_mode)) {
			/* for the next cycle, point the dir inode at our new directory */
			memcpy(&dir_inode, &inode, sizeof(struct ext2_inode));
		} else {
			if (!done) {
				/* we aren't done and this walked over a nondir, abort */
				LTRACEF("not finished and component is nondir\n");
				return ERR_NOT_FOUND;
			}
		}

		if (!done) {
			/* move to the next seperator */
			ptr = next_sep + 1; 

			/* consume multiple seperators */
			while (*ptr == '/')
				ptr++;
		}
	}

	return 0;
}

/* do a path parse, looking up each component */
int ext2_lookup(ext2_t *ext2, const char *_path, inodenum_t *inum)
{
	LTRACEF("path '%s', inum %p\n", _path, inum);

	char path[512];
	strlcpy(path, _path, sizeof(path));

	return ext2_walk(ext2, path, &ext2->root_inode, inum, 1);
}