namei.c

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		if (!permission(dir,MAY_WRITE)) {		//如果此目录的权限是不可写的，返回
			iput(dir);
			return -EACCES;
		}
		inode = new_inode(dir->i_dev);	//为在这个目录中不存在的文件建立一个新的inode
		if (!inode) {
			iput(dir);
			return -ENOSPC;
		}
		inode->i_mode = mode;		//设置新的inode的mode
		inode->i_dirt = 1;
		bh = add_entry(dir,basename,namelen,&de);		//在目录文件中写入de->name
		if (!bh) {
			inode->i_nlinks--;
			iput(inode);
			iput(dir);
			return -ENOSPC;
		}
		de->inode = inode->i_num;		//将de->inode写入实际块号，它将在dir中与de->name对照
		bh->b_dirt = 1;
		brelse(bh);
		iput(dir);
		*res_inode = inode;
		return 0;
	}
	inr = de->inode;
	dev = dir->i_dev;
	brelse(bh);
	iput(dir);
	if (flag & O_EXCL)				//如果flag是检查该文件有没有
		return -EEXIST;
	if (!(inode=iget(dev,inr)))			//取该文件的inode
		return -EACCES;
	if ((S_ISDIR(inode->i_mode) && (flag & O_ACCMODE)) ||
	    permission(inode,ACC_MODE(flag))!=ACC_MODE(flag)) {
		iput(inode);
		return -EPERM;
	}
	inode->i_atime = CURRENT_TIME;
	if (flag & O_TRUNC)
		truncate(inode);
	*res_inode = inode;
	return 0;
}

int sys_mkdir(const char * pathname, int mode)
{
	const char * basename;
	int namelen;
	struct m_inode * dir, * inode;
	struct buffer_head * bh, *dir_block;
	struct dir_entry * de;

	if (current->euid && current->uid)
		return -EPERM;
	if (!(dir = dir_namei(pathname,&namelen,&basename)))		//读取待建目录的那个目录
		return -ENOENT;
	if (!namelen) {
		iput(dir);
		return -ENOENT;
	}
	if (!permission(dir,MAY_WRITE)) {		//检查此目录的写权限
		iput(dir);
		return -EPERM;
	}
	bh = find_entry(dir,basename,namelen,&de);	//在这个目录文件中是否有待建目录的名字
	if (bh) {
		brelse(bh);
		iput(dir);
		return -EEXIST;
	}
	inode = new_inode(dir->i_dev);		//创建一个新的inode
	if (!inode) {
		iput(dir);
		return -ENOSPC;
	}
	inode->i_size = 32;
	inode->i_dirt = 1;
	inode->i_mtime = inode->i_atime = CURRENT_TIME;
	if (!(inode->i_zone[0]=new_block(inode->i_dev))) {	//为该目录节点创建第一个块
		iput(dir);
		inode->i_nlinks--;
		iput(inode);
		return -ENOSPC;
	}
	inode->i_dirt = 1;
	if (!(dir_block=bread(inode->i_dev,inode->i_zone[0]))) {	//读该目录块
		iput(dir);
		free_block(inode->i_dev,inode->i_zone[0]);
		inode->i_nlinks--;
		iput(inode);
		return -ERROR;
	}
	de = (struct dir_entry *) dir_block->b_data;		//de指向该块的数据区
	de->inode=inode->i_num;			//建立本目录的入口
	strcpy(de->name,".");
	de++;
	de->inode = dir->i_num;			//建立父目录的入口
	strcpy(de->name,"..");
	inode->i_nlinks = 2;
	dir_block->b_dirt = 1;
	brelse(dir_block);
	inode->i_mode = I_DIRECTORY | (mode & 0777 & ~current->umask);	//将本节点设为目录文件
	inode->i_dirt = 1;
	bh = add_entry(dir,basename,namelen,&de);		//在父目录中登记本目录文件
	if (!bh) {
		iput(dir);
		free_block(inode->i_dev,inode->i_zone[0]);
		inode->i_nlinks=0;
		iput(inode);
		return -ENOSPC;
	}
	de->inode = inode->i_num;
	bh->b_dirt = 1;
	dir->i_nlinks++;
	dir->i_dirt = 1;
	iput(dir);
	iput(inode);
	brelse(bh);
	return 0;
}

/*
 * routine to check that the specified directory is empty (for rmdir)
 */
static int empty_dir(struct m_inode * inode)
{
	int nr,block;
	int len;
	struct buffer_head * bh;
	struct dir_entry * de;

	len = inode->i_size / sizeof (struct dir_entry);	//本目录中有几个项目
	if (len<2 || !inode->i_zone[0] ||
	    !(bh=bread(inode->i_dev,inode->i_zone[0]))) {	//检查目录是否为有效目录
	    	printk("warning - bad directory on dev %04x\n",inode->i_dev);
		return 0;
	}
	de = (struct dir_entry *) bh->b_data;			//de指向目录中的元素
	if (de[0].inode != inode->i_num || !de[1].inode || 
	    strcmp(".",de[0].name) || strcmp("..",de[1].name)) {	//检查元素中的第一项是否为“。”和第二项是否为“。。”
	    	printk("warning - bad directory on dev %04x\n",inode->i_dev);
		return 0;
	}
	nr = 2;
	de += 2;
	while (nr<len) {
		if ((void *) de >= (void *) (bh->b_data+BLOCK_SIZE)) {		//如果该目录文件很大，超过了本块
			brelse(bh);
			block=bmap(inode,nr/DIR_ENTRIES_PER_BLOCK);	//找本目录的下一个块
			if (!block) {
				nr += DIR_ENTRIES_PER_BLOCK;
				continue;
			}
			if (!(bh=bread(inode->i_dev,block)))		//读取该块
				return 0;
			de = (struct dir_entry *) bh->b_data;		//重新定位指针de
		}
		if (de->inode) {			//如果目录文件中只有本目录和父目录项，那么就是null目录
			brelse(bh);
			return 0;
		}
		de++;
		nr++;
	}
	brelse(bh);
	return 1;
}

int sys_rmdir(const char * name)
{
	const char * basename;
	int namelen;
	struct m_inode * dir, * inode;
	struct buffer_head * bh;
	struct dir_entry * de;

	if (current->euid && current->uid)
		return -EPERM;
	if (!(dir = dir_namei(name,&namelen,&basename)))
		return -ENOENT;
	if (!namelen) {
		iput(dir);
		return -ENOENT;
	}
	bh = find_entry(dir,basename,namelen,&de);	//在目录文件找是否有要删除的那个目录项
	if (!bh) {
		iput(dir);
		return -ENOENT;
	}
	if (!permission(dir,MAY_WRITE)) {			//检查写权限
		iput(dir);
		brelse(bh);
		return -EPERM;
	}
	if (!(inode = iget(dir->i_dev, de->inode))) {	//取要删除的那个文件的inode
		iput(dir);
		brelse(bh);
		return -EPERM;
	}
	if (inode == dir) {	/* we may not delete ".", but "../dir" is ok */		//要删除的目录不能是父目录
		iput(inode);
		iput(dir);
		brelse(bh);
		return -EPERM;
	}
	if (!S_ISDIR(inode->i_mode)) {			//此节点必须是目录
		iput(inode);
		iput(dir);
		brelse(bh);
		return -ENOTDIR;
	}
	if (!empty_dir(inode)) {				//此节点是否为空
		iput(inode);
		iput(dir);
		brelse(bh);
		return -ENOTEMPTY;
	}
	if (inode->i_nlinks != 2)
		printk("empty directory has nlink!=2 (%d)",inode->i_nlinks);
	de->inode = 0;					//在父目录中清除该目录的节点
	bh->b_dirt = 1;
	brelse(bh);
	inode->i_nlinks=0;
	inode->i_dirt=1;
	dir->i_nlinks--;
	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
	dir->i_dirt=1;
	iput(dir);
	iput(inode);
	return 0;
}

int sys_unlink(const char * name)
{
	const char * basename;
	int namelen;
	struct m_inode * dir, * inode;
	struct buffer_head * bh;
	struct dir_entry * de;

	if (!(dir = dir_namei(name,&namelen,&basename)))
		return -ENOENT;
	if (!namelen) {
		iput(dir);
		return -ENOENT;
	}
	if (!permission(dir,MAY_WRITE)) {
		iput(dir);
		return -EPERM;
	}
	bh = find_entry(dir,basename,namelen,&de);
	if (!bh) {
		iput(dir);
		return -ENOENT;
	}
	inode = iget(dir->i_dev, de->inode);
	if (!inode) {					//不能联结不存在的文件
		printk("iget failed in delete (%04x:%d)",dir->i_dev,de->inode);
		iput(dir);
		brelse(bh);
		return -ENOENT;
	}
	if (!S_ISREG(inode->i_mode)) {		//是否为正常的节点mode
		iput(inode);
		iput(dir);
		brelse(bh);
		return -EPERM;
	}
	if (!inode->i_nlinks) {
		printk("Deleting nonexistent file (%04x:%d), %d\n",
			inode->i_dev,inode->i_num,inode->i_nlinks);
		inode->i_nlinks=1;
	}
	de->inode = 0;
	bh->b_dirt = 1;
	brelse(bh);
	inode->i_nlinks--;
	inode->i_dirt = 1;
	inode->i_ctime = CURRENT_TIME;
	iput(inode);
	iput(dir);
	return 0;
}

int sys_link(const char * oldname, const char * newname)
{
	struct dir_entry * de;
	struct m_inode * oldinode, * dir;
	struct buffer_head * bh;
	const char * basename;
	int namelen;

	oldinode=namei(oldname);			//保存老文件名的inode
	if (!oldinode)
		return -ENOENT;
	if (!S_ISREG(oldinode->i_mode)) {		//必须是正常文件
		iput(oldinode);
		return -EPERM;
	}
	dir = dir_namei(newname,&namelen,&basename);	//找出newname的父目录节点
	if (!dir) {
		iput(oldinode);
		return -EACCES;
	}
	if (!namelen) {
		iput(oldinode);
		iput(dir);
		return -EPERM;
	}
	if (dir->i_dev != oldinode->i_dev) {
		iput(dir);
		iput(oldinode);
		return -EXDEV;
	}
	if (!permission(dir,MAY_WRITE)) {
		iput(dir);
		iput(oldinode);
		return -EACCES;
	}
	bh = find_entry(dir,basename,namelen,&de);	//看看父目录中是否有这个名字
	if (bh) {						//如果有，就不能建立
		brelse(bh);
		iput(dir);
		iput(oldinode);
		return -EEXIST;
	}
	bh = add_entry(dir,basename,namelen,&de);		//在父目录中为这个名字建立一个入口点
	if (!bh) {
		iput(dir);
		iput(oldinode);
		return -ENOSPC;
	}
	de->inode = oldinode->i_num;			//将此节点指向和oldinode一样的inode
	bh->b_dirt = 1;
	brelse(bh);
	iput(dir);
	oldinode->i_nlinks++;
	oldinode->i_ctime = CURRENT_TIME;
	oldinode->i_dirt = 1;
	iput(oldinode);
	return 0;
}