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文件读写主要是通过inode结构里的数据，读取或者写入到底层的硬盘中，并更新相应的属性。

/* *  linux/fs/read_write.c * *  (C) 1991  Linus Torvalds */#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         extern int rw_char(int rw,int dev, char * buf, int count, off_t * pos);extern int read_pipe(struct m_inode * inode, char * buf, int count);extern int write_pipe(struct m_inode * inode, char * buf, int count);extern int block_read(int dev, off_t * pos, char * buf, int count);extern int block_write(int dev, off_t * pos, char * buf, int count);extern int file_read(struct m_inode * inode, struct file * filp, char * buf, int count);extern int file_write(struct m_inode * inode, struct file * filp, char * buf, int count);int sys_lseek(unsigned int fd,off_t offset, int origin){ struct file * file; int tmp; if (fd >= NR_OPEN || !(file=current->filp[fd]) || !(file->f_inode) || !IS_SEEKABLE(MAJOR(file->f_inode->i_dev))) return -EBADF; if (file->f_inode->i_pipe) return -ESPIPE; // SEEK_SET,SEEK_CUR和SEEK_END和依次为0，1和2 switch (origin) { case 0: if (offset<0) return -EINVAL; file->f_pos=offset; break; case 1: // 这个时候可以offset可以传负数，但是不能大于当前偏移 if (file->f_pos+offset<0) return -EINVAL; file->f_pos += offset; break; case 2: if ((tmp=file->f_inode->i_size+offset) < 0) return -EINVAL; file->f_pos = tmp; break; default: return -EINVAL; } return file->f_pos;}int sys_read(unsigned int fd,char * buf,int count){ struct file * file; struct m_inode * inode; if (fd>=NR_OPEN || count<0 || !(file=current->filp[fd])) return -EINVAL; if (!count) return 0; verify_area(buf,count); inode = file->f_inode; // 该文件描述符对应的是一个管道文件，并且是读端则读管道 if (inode->i_pipe) return (file->f_mode&1)?read_pipe(inode,buf,count):-EIO; if (S_ISCHR(inode->i_mode)) return rw_char(READ,inode->i_zone[0],buf,count,&file->f_pos); if (S_ISBLK(inode->i_mode)) return block_read(inode->i_zone[0],&file->f_pos,buf,count); if (S_ISDIR(inode->i_mode) || S_ISREG(inode->i_mode)) { // 读的长度不能大于剩下的可读长度 if (count+file->f_pos > inode->i_size) count = inode->i_size - file->f_pos; // 到底了 if (count<=0) return 0; return file_read(inode,file,buf,count); } printk("(Read)inode->i_mode=%06o\n\r",inode->i_mode); return -EINVAL;}int sys_write(unsigned int fd,char * buf,int count){ struct file * file; struct m_inode * inode; if (fd>=NR_OPEN || count <0 || !(file=current->filp[fd])) return -EINVAL; if (!count) return 0; inode=file->f_inode; if (inode->i_pipe) return (file->f_mode&2)?write_pipe(inode,buf,count):-EIO; if (S_ISCHR(inode->i_mode)) return rw_char(WRITE,inode->i_zone[0],buf,count,&file->f_pos); if (S_ISBLK(inode->i_mode)) return block_write(inode->i_zone[0],&file->f_pos,buf,count); if (S_ISREG(inode->i_mode)) return file_write(inode,file,buf,count); printk("(Write)inode->i_mode=%06o\n\r",inode->i_mode); return -EINVAL;}
        
       
      
     
    
   

/* *  linux/fs/file_dev.c * *  (C) 1991  Linus Torvalds */#include 
   
    #include 
    
     #include 
     
      #include 
      
       #include 
       
        #define MIN(a,b) (((a)<(b))?(a):(b))#define MAX(a,b) (((a)>(b))?(a):(b))int file_read(struct m_inode * inode, struct file * filp, char * buf, int count){   	int left,chars,nr;	struct buffer_head * bh;	if ((left=count)<=0)		return 0;	while (left) {   		// bmap取得该文件偏移对应的硬盘块号，然后读进来		if (nr = bmap(inode,(filp->f_pos)/BLOCK_SIZE)) {   			if (!(bh=bread(inode->i_dev,nr)))				break;		} else			bh = NULL;		// 偏移		nr = filp->f_pos % BLOCK_SIZE;		// 读进来的数据中，可读的长度和还需要读的长度，取小的，如果还没读完继续把块从硬盘读进来		chars = MIN( BLOCK_SIZE-nr , left );		filp->f_pos += chars; // 更新偏移指针		left -= chars; // 更新还需药读取的长度		if (bh) {   			char * p = nr + bh->b_data;			while (chars-->0)				put_fs_byte(*(p++),buf++); //复制到buf里 			brelse(bh);		} else {   			while (chars-->0)				put_fs_byte(0,buf++);		}	}	// 更新访问时间	inode->i_atime = CURRENT_TIME;	// 返回读取的长度，如果一个都没读则返回错误	return (count-left)?(count-left):-ERROR;}int file_write(struct m_inode * inode, struct file * filp, char * buf, int count){   	off_t pos;	int block,c;	struct buffer_head * bh;	char * p;	int i=0;/* * ok, append may not work when many processes are writing at the same time * but so what. That way leads to madness anyway. */	// 如果设置了追加标记位，则更新当前位置指针到文件最后一个字节	if (filp->f_flags & O_APPEND)		pos = inode->i_size;	else		pos = filp->f_pos;	// i为已经写入的长度，count为需要写入的长度	while (i
        
         i_dev,block))) break; c = pos % BLOCK_SIZE; p = c + bh->b_data; // 开始写入数据的位置 bh->b_dirt = 1; // 标记数据需要回写硬盘 c = BLOCK_SIZE-c; // 算出能写的长度 if (c > count-i) c = count-i; // 比较能写的长度和还需要写的长度，取小的 pos += c; // 更新偏移指针，c为准备写入的长度 // 如果超过原来长度则需要更新i_size字段，标记inode需要回写 if (pos > inode->i_size) { inode->i_size = pos; inode->i_dirt = 1; } i += c; // 更新已经写入的长度 while (c-->0) *(p++) = get_fs_byte(buf++); brelse(bh); } inode->i_mtime = CURRENT_TIME; if (!(filp->f_flags & O_APPEND)) { filp->f_pos = pos; inode->i_ctime = CURRENT_TIME; } return (i?i:-1);}
        
       
      
     
    
   

static void cp_stat(struct m_inode * inode, struct stat * statbuf){   	struct stat tmp;	int i;	verify_area(statbuf,sizeof (* statbuf));	tmp.st_dev = inode->i_dev;	tmp.st_ino = inode->i_num;	tmp.st_mode = inode->i_mode;	tmp.st_nlink = inode->i_nlinks;	tmp.st_uid = inode->i_uid;	tmp.st_gid = inode->i_gid;	tmp.st_rdev = inode->i_zone[0];	tmp.st_size = inode->i_size;	tmp.st_atime = inode->i_atime;	tmp.st_mtime = inode->i_mtime;	tmp.st_ctime = inode->i_ctime;	for (i=0 ; i
   
    = NR_OPEN || !(f=current->filp[fd]) || !(inode=f->f_inode))		return -EBADF;	cp_stat(inode,statbuf);	return 0;}
   

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