Files Implementation

// fs/read_write.c
int sys_write(int fd, const char* buf, int count) 
{
	struct file *file = current->filp[fd];
  struct m_inode *inode = file->inode;
  if(S_ISREG(inode->i_mode))
		return file_write(inode, file, buf, count); 
}

1. 需要知道是哪段字符，file中一个读写指针是开始地址，可以通过fseek修改；

2. 通过inode找到对应的盘块号；

3. 用盘块号、buf等形成request放入电梯算法

int file_write(struct m_inode *inode, struct file 
	*filp, char *buf, int count)
{
	off_t pos;
	if(filp->f_flags&O_APPEND)
		pos=inode->i_size; 
	else pos=filp->f_pos;
	// ...

while(i<count){
	block=create_block(inode, pos/BLOCK_SIZE);
	bh=bread(inode->i_dev, block);
	int c=pos%BLOCK_SIZE; 
	char *p=c+bh->b_data;
	bh->b_dirt=1; 
	c=BLOCK_SIZE-c; 
	pos+=c;
	... 
	while(c-->0) *(p++)=get_fs_byte(buf++);
	brelse(bh); 
}
filp->f_pos=pos; 

int _bmap(m_inode *inode, int block, int create)
{
	if(block<7){
		if(create&&!inode->i_zone[block]) {
			inode->i_zone[block]=new_block(inode->i_dev);
			inode->i_ctime=CURRENT_TIME;
			inode->i_dirt=1;
		}
    return inode->i_zone[block];
	}
	block-=7;
	if(block<512){ 
		bh=bread(inode->i_dev,inode->i_zone[7]);
		return (bh->b_data)[block];
	}
	// ...
}

struct d_inode{
	unsigned short i_mode;
	// ...
  unsigned short i_zone[9];
	//(0-6):直接数据块，(7):一重间接，(8):二重间接 
}

struct m_inode{ //读入内存后的inode 
	unsigned short i_mode; //文件的类型和属性 ...
	unsigned short i_zone[9]; //指向文件内容数据块 
	struct task_struct *i_wait;
  unsigned short i_count;
	unsigned char i_lock;
	unsigned char i_dirt;  
	//... 
}

int sys_open(const char* filename, int flag)
{
	if(S_ISCHR(inode->i_mode)){ //字符设备
		if(MAJOR(inode->i_zone[0])==4) //设备文件
			current->tty=MINOR(inode->i_zone[0]);
}

#define MAJOR(a)(((unsigned)(a))>>8)) //取高字节 
#define MINOR(a)((a)&0xff) //取低字节