namei.c

讲述linux的初始化过程

	struct buffer_head * dir_block;
	struct ext2_dir_entry_2 * de;
	int err;

	if (dir->i_nlink >= EXT2_LINK_MAX)
		return -EMLINK;

	inode = ext2_new_inode (dir, S_IFDIR);
	err = PTR_ERR(inode);
	if (IS_ERR(inode))
		return err;

	inode->i_op = &ext2_dir_inode_operations;
	inode->i_fop = &ext2_dir_operations;
	inode->i_size = inode->i_sb->s_blocksize;
	inode->i_blocks = 0;	
	dir_block = ext2_bread (inode, 0, 1, &err);
	if (!dir_block) {
		inode->i_nlink--; /* is this nlink == 0? */
		mark_inode_dirty(inode);
		iput (inode);
		return err;
	}
	de = (struct ext2_dir_entry_2 *) dir_block->b_data;
	de->inode = cpu_to_le32(inode->i_ino);
	de->name_len = 1;
	de->rec_len = cpu_to_le16(EXT2_DIR_REC_LEN(de->name_len));
	strcpy (de->name, ".");
	ext2_set_de_type(dir->i_sb, de, S_IFDIR);
	de = (struct ext2_dir_entry_2 *) ((char *) de + le16_to_cpu(de->rec_len));
	de->inode = cpu_to_le32(dir->i_ino);
	de->rec_len = cpu_to_le16(inode->i_sb->s_blocksize - EXT2_DIR_REC_LEN(1));
	de->name_len = 2;
	strcpy (de->name, "..");
	ext2_set_de_type(dir->i_sb, de, S_IFDIR);
	inode->i_nlink = 2;
	mark_buffer_dirty_inode(dir_block, dir);
	brelse (dir_block);
	inode->i_mode = S_IFDIR | mode;
	if (dir->i_mode & S_ISGID)
		inode->i_mode |= S_ISGID;
	mark_inode_dirty(inode);
	err = ext2_add_entry (dir, dentry->d_name.name, dentry->d_name.len, 
			     inode);
	if (err)
		goto out_no_entry;
	dir->i_nlink++;
	dir->u.ext2_i.i_flags &= ~EXT2_BTREE_FL;
	mark_inode_dirty(dir);
	d_instantiate(dentry, inode);
	return 0;

out_no_entry:
	inode->i_nlink = 0;
	mark_inode_dirty(inode);
	iput (inode);
	return err;
}

/*
 * routine to check that the specified directory is empty (for rmdir)
 */
static int empty_dir (struct inode * inode)
{
	unsigned long offset;
	struct buffer_head * bh;
	struct ext2_dir_entry_2 * de, * de1;
	struct super_block * sb;
	int err;

	sb = inode->i_sb;
	if (inode->i_size < EXT2_DIR_REC_LEN(1) + EXT2_DIR_REC_LEN(2) ||
	    !(bh = ext2_bread (inode, 0, 0, &err))) {
	    	ext2_warning (inode->i_sb, "empty_dir",
			      "bad directory (dir #%lu) - no data block",
			      inode->i_ino);
		return 1;
	}
	de = (struct ext2_dir_entry_2 *) bh->b_data;
	de1 = (struct ext2_dir_entry_2 *) ((char *) de + le16_to_cpu(de->rec_len));
	if (le32_to_cpu(de->inode) != inode->i_ino || !le32_to_cpu(de1->inode) || 
	    strcmp (".", de->name) || strcmp ("..", de1->name)) {
	    	ext2_warning (inode->i_sb, "empty_dir",
			      "bad directory (dir #%lu) - no `.' or `..'",
			      inode->i_ino);
		brelse (bh);
		return 1;
	}
	offset = le16_to_cpu(de->rec_len) + le16_to_cpu(de1->rec_len);
	de = (struct ext2_dir_entry_2 *) ((char *) de1 + le16_to_cpu(de1->rec_len));
	while (offset < inode->i_size ) {
		if (!bh || (void *) de >= (void *) (bh->b_data + sb->s_blocksize)) {
			brelse (bh);
			bh = ext2_bread (inode, offset >> EXT2_BLOCK_SIZE_BITS(sb), 0, &err);
			if (!bh) {
#if 0
				ext2_error (sb, "empty_dir",
					    "directory #%lu contains a hole at offset %lu",
					    inode->i_ino, offset);
#endif
				offset += sb->s_blocksize;
				continue;
			}
			de = (struct ext2_dir_entry_2 *) bh->b_data;
		}
		if (!ext2_check_dir_entry ("empty_dir", inode, de, bh,
					   offset)) {
			brelse (bh);
			return 1;
		}
		if (le32_to_cpu(de->inode)) {
			brelse (bh);
			return 0;
		}
		offset += le16_to_cpu(de->rec_len);
		de = (struct ext2_dir_entry_2 *) ((char *) de + le16_to_cpu(de->rec_len));
	}
	brelse (bh);
	return 1;
}

static int ext2_rmdir (struct inode * dir, struct dentry *dentry)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry_2 * de;

	retval = -ENOENT;
	bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de);
	if (!bh)
		goto end_rmdir;

	inode = dentry->d_inode;
	DQUOT_INIT(inode);

	retval = -EIO;
	if (le32_to_cpu(de->inode) != inode->i_ino)
		goto end_rmdir;

	retval = -ENOTEMPTY;
	if (!empty_dir (inode))
		goto end_rmdir;

	retval = ext2_delete_entry(dir, de, bh);
	if (retval)
		goto end_rmdir;
	if (inode->i_nlink != 2)
		ext2_warning (inode->i_sb, "ext2_rmdir",
			      "empty directory has nlink!=2 (%d)",
			      inode->i_nlink);
	inode->i_version = ++event;
	inode->i_nlink = 0;
	inode->i_size = 0;
	mark_inode_dirty(inode);
	dir->i_nlink--;
	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
	dir->u.ext2_i.i_flags &= ~EXT2_BTREE_FL;
	mark_inode_dirty(dir);

end_rmdir:
	brelse (bh);
	return retval;
}

static int ext2_unlink(struct inode * dir, struct dentry *dentry)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry_2 * de;

	retval = -ENOENT;
	bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de);
	if (!bh)
		goto end_unlink;

	inode = dentry->d_inode;
	DQUOT_INIT(inode);

	retval = -EIO;
	if (le32_to_cpu(de->inode) != inode->i_ino)
		goto end_unlink;
	
	if (!inode->i_nlink) {
		ext2_warning (inode->i_sb, "ext2_unlink",
			      "Deleting nonexistent file (%lu), %d",
			      inode->i_ino, inode->i_nlink);
		inode->i_nlink = 1;
	}
	retval = ext2_delete_entry(dir, de, bh);
	if (retval)
		goto end_unlink;
	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
	dir->u.ext2_i.i_flags &= ~EXT2_BTREE_FL;
	mark_inode_dirty(dir);
	inode->i_nlink--;
	mark_inode_dirty(inode);
	inode->i_ctime = dir->i_ctime;
	retval = 0;

end_unlink:
	brelse (bh);
	return retval;
}

static int ext2_symlink (struct inode * dir, struct dentry *dentry, const char * symname)
{
	struct inode * inode;
	int l, err;

	l = strlen(symname)+1;
	if (l > dir->i_sb->s_blocksize)
		return -ENAMETOOLONG;

	inode = ext2_new_inode (dir, S_IFLNK);
	err = PTR_ERR(inode);
	if (IS_ERR(inode))
		return err;

	inode->i_mode = S_IFLNK | S_IRWXUGO;

	if (l > sizeof (inode->u.ext2_i.i_data)) {
		inode->i_op = &page_symlink_inode_operations;
		inode->i_mapping->a_ops = &ext2_aops;
		err = block_symlink(inode, symname, l);
		if (err)
			goto out_no_entry;
	} else {
		inode->i_op = &ext2_fast_symlink_inode_operations;
		memcpy((char*)&inode->u.ext2_i.i_data,symname,l);
		inode->i_size = l-1;
	}
	mark_inode_dirty(inode);

	err = ext2_add_entry (dir, dentry->d_name.name, dentry->d_name.len, 
			     inode);
	if (err)
		goto out_no_entry;
	d_instantiate(dentry, inode);
	return 0;

out_no_entry:
	inode->i_nlink--;
	mark_inode_dirty(inode);
	iput (inode);
	return err;
}

static int ext2_link (struct dentry * old_dentry,
		struct inode * dir, struct dentry *dentry)
{
	struct inode *inode = old_dentry->d_inode;
	int err;

	if (S_ISDIR(inode->i_mode))
		return -EPERM;

	if (inode->i_nlink >= EXT2_LINK_MAX)
		return -EMLINK;
	
	err = ext2_add_entry (dir, dentry->d_name.name, dentry->d_name.len, 
			     inode);
	if (err)
		return err;

	inode->i_nlink++;
	inode->i_ctime = CURRENT_TIME;
	mark_inode_dirty(inode);
	atomic_inc(&inode->i_count);
	d_instantiate(dentry, inode);
	return 0;
}

#define PARENT_INO(buffer) \
	((struct ext2_dir_entry_2 *) ((char *) buffer + \
	le16_to_cpu(((struct ext2_dir_entry_2 *) buffer)->rec_len)))->inode

/*
 * Anybody can rename anything with this: the permission checks are left to the
 * higher-level routines.
 */
static int ext2_rename (struct inode * old_dir, struct dentry *old_dentry,
			   struct inode * new_dir,struct dentry *new_dentry)
{
	struct inode * old_inode, * new_inode;
	struct buffer_head * old_bh, * new_bh, * dir_bh;
	struct ext2_dir_entry_2 * old_de, * new_de;
	int retval;

	old_bh = new_bh = dir_bh = NULL;

	old_bh = ext2_find_entry (old_dir, old_dentry->d_name.name, old_dentry->d_name.len, &old_de);
	/*
	 *  Check for inode number is _not_ due to possible IO errors.
	 *  We might rmdir the source, keep it as pwd of some process
	 *  and merrily kill the link to whatever was created under the
	 *  same name. Goodbye sticky bit ;-<
	 */
	old_inode = old_dentry->d_inode;
	retval = -ENOENT;
	if (!old_bh || le32_to_cpu(old_de->inode) != old_inode->i_ino)
		goto end_rename;

	new_inode = new_dentry->d_inode;
	new_bh = ext2_find_entry (new_dir, new_dentry->d_name.name,
				new_dentry->d_name.len, &new_de);
	if (new_bh) {
		if (!new_inode) {
			brelse (new_bh);
			new_bh = NULL;
		} else {
			DQUOT_INIT(new_inode);
		}
	}
	if (S_ISDIR(old_inode->i_mode)) {
		if (new_inode) {
			retval = -ENOTEMPTY;
			if (!empty_dir (new_inode))
				goto end_rename;
		}
		retval = -EIO;
		dir_bh = ext2_bread (old_inode, 0, 0, &retval);
		if (!dir_bh)
			goto end_rename;
		if (le32_to_cpu(PARENT_INO(dir_bh->b_data)) != old_dir->i_ino)
			goto end_rename;
		retval = -EMLINK;
		if (!new_inode && new_dir!=old_dir &&
				new_dir->i_nlink >= EXT2_LINK_MAX)
			goto end_rename;
	}
	if (!new_bh) {
		retval = ext2_add_entry (new_dir, new_dentry->d_name.name,
					 new_dentry->d_name.len,
					 old_inode);
		if (retval)
			goto end_rename;
	} else {
		new_de->inode = le32_to_cpu(old_inode->i_ino);
		if (EXT2_HAS_INCOMPAT_FEATURE(new_dir->i_sb,
					      EXT2_FEATURE_INCOMPAT_FILETYPE))
			new_de->file_type = old_de->file_type;
		new_dir->i_version = ++event;
		mark_buffer_dirty_inode(new_bh, new_dir);
		if (IS_SYNC(new_dir)) {
			ll_rw_block (WRITE, 1, &new_bh);
			wait_on_buffer (new_bh);
		}
		brelse(new_bh);
		new_bh = NULL;
	}
	
	/*
	 * Like most other Unix systems, set the ctime for inodes on a
	 * rename.
	 */
	old_inode->i_ctime = CURRENT_TIME;
	mark_inode_dirty(old_inode);

	/*
	 * ok, that's it
	 */
	ext2_delete_entry(old_dir, old_de, old_bh);

	if (new_inode) {
		new_inode->i_nlink--;
		new_inode->i_ctime = CURRENT_TIME;
		mark_inode_dirty(new_inode);
	}
	old_dir->i_ctime = old_dir->i_mtime = CURRENT_TIME;
	old_dir->u.ext2_i.i_flags &= ~EXT2_BTREE_FL;
	mark_inode_dirty(old_dir);
	if (dir_bh) {
		PARENT_INO(dir_bh->b_data) = le32_to_cpu(new_dir->i_ino);
		mark_buffer_dirty_inode(dir_bh, old_inode);
		old_dir->i_nlink--;
		mark_inode_dirty(old_dir);
		if (new_inode) {
			new_inode->i_nlink--;
			mark_inode_dirty(new_inode);
		} else {
			new_dir->i_nlink++;
			new_dir->u.ext2_i.i_flags &= ~EXT2_BTREE_FL;
			mark_inode_dirty(new_dir);
		}
	}

	retval = 0;

end_rename:
	brelse (dir_bh);
	brelse (old_bh);
	brelse (new_bh);
	return retval;
}

/*
 * directories can handle most operations...
 */
struct inode_operations ext2_dir_inode_operations = {
	create:		ext2_create,
	lookup:		ext2_lookup,
	link:		ext2_link,
	unlink:		ext2_unlink,
	symlink:	ext2_symlink,
	mkdir:		ext2_mkdir,
	rmdir:		ext2_rmdir,
	mknod:		ext2_mknod,
	rename:		ext2_rename,
};