《操作系统真象还原》第十四章 ---- 实现文件系统任务繁多饭得一口口吃路得一步步走啊（中二）

我就是我 2022-09-04 01:50 108阅读 0赞

### 文章目录 ###

*   *  专栏博客链接
     *  相关查阅博客链接
     *  本书中错误勘误
     *  实现文件读取
     *   *  编写完的file.c（file\_read）
         *  编写完的fs.c（sys\_read）
         *  修改后的main.c
         *  make all 验证成果
     *  实现文件读写指针定位
     *   *  编写后的fs.h（enum whence）
         *  编写后的fs.c（sys\_lseek）
         *  编写后的main.c
         *  make all 验证成果

--------------------

## 专栏博客链接 ##

--------------------

**[《操作系统真象还原》从零开始自制操作系统 全章节博客链接][Link 1]**

--------------------

## 相关查阅博客链接 ##

--------------------

**[为什么叫lseek()][lseek]**

--------------------

## 本书中错误勘误 ##

--------------------

**1、`fs/file.c`编写`file_read`  
里面`io_buf`内存分配失败的时候 没有`return -1` 加一个即可**

--------------------

## 实现文件读取 ##

--------------------

### 编写完的file.c（file\_read） ###

--------------------

int32_t file_read(struct file* file,void* buf,uint32_t count)
    { 
        uint8_t* buf_dst = (uint8_t*)buf;
        uint32_t size = count ,size_left = count;
        
        //如果要读取的内容比原本文件的字节数更多 则重新设置size 如果到底了 就直接退出
        if((file->fd_pos + count) > file->fd_inode->i_size)
        { 
            size = file->fd_inode->i_size - file->fd_pos;
            size_left = size;
            if(size == 0)
                return -1;
        }
        
        uint8_t* io_buf = (uint8_t*)sys_malloc(BLOCK_SIZE);
        if(io_buf == NULL)
        { 
            printk("file_read: sys_malloc for io_buf failed\n");
            return -1;	//书上没写
        }
        
        uint32_t* all_blocks = (uint32_t*)sys_malloc(BLOCK_SIZE + 48);//48 + 512 = 560
        if(all_blocks == NULL)
        { 
            printk("file_read: sys_malloc for io_buf failed\n");
            return -1;
        }
        
        uint32_t block_read_start_idx = file->fd_pos / BLOCK_SIZE;           //开始读取的扇区号
        uint32_t block_read_end_idx   = (file->fd_pos + count) / BLOCK_SIZE; //结束读取的扇区号
        uint32_t read_blocks          = block_read_end_idx - block_read_start_idx;
        
        ASSERT(block_read_start_idx < 139 && block_read_end_idx < 139);	    
        
        int32_t indirect_block_table;
        uint32_t block_idx;
        
        if(read_blocks == 0) //没有增量 则就在原扇区读
        { 
        	ASSERT(block_read_end_idx == block_read_start_idx);
        	if(block_read_end_idx < 12)		//在直接块中
        	{ 
        	    block_idx = block_read_end_idx;
        	    all_blocks[block_idx] = file->fd_inode->i_sectors[block_idx];
        	}
        	else
        	{ 
        	    ASSERT(file->fd_inode->i_sectors[12] != 0); 
        	    indirect_block_table = file->fd_inode->i_sectors[12];
        	    ide_read(cur_part->my_disk,indirect_block_table,all_blocks + 12,1);
        	}
        }
        else	//有增量
        { 
        	if(block_read_end_idx < 12)		//在直接块中
        	{ 
        	    block_idx = block_read_start_idx;
        	    while(block_idx <= block_read_end_idx)
        	    { 
        	    	all_blocks[block_idx] = file->fd_inode->i_sectors[block_idx];
        	    	++block_idx;
        	    }
        	}
        	else if(block_read_start_idx < 12 && block_read_end_idx >= 12) //越界
        	{ 
        	    block_idx = block_read_start_idx;
        	    while(block_idx < 12)
        	    { 
        	    	all_blocks[block_idx] = file->fd_inode->i_sectors[block_idx];
        	    	++block_idx;
        	    }
        	    indirect_block_table = file->fd_inode->i_sectors[12];
        	    ide_read(cur_part->my_disk,indirect_block_table,all_blocks + 12,1);
        	}
        	else if(block_read_start_idx >= 12)
        	{ 
        	    ASSERT(file->fd_inode->i_sectors[12] != 0); 
        	    indirect_block_table = file->fd_inode->i_sectors[12];
        	    ide_read(cur_part->my_disk,indirect_block_table,all_blocks + 12,1);
        	}
        }
        
        //开始读数据
        uint32_t sec_idx,sec_lba,sec_off_bytes,sec_left_bytes,chunk_size;
        uint32_t bytes_read = 0;
        
        while(bytes_read < size)
        { 
        	sec_idx = file->fd_pos / BLOCK_SIZE;
        	sec_lba = all_blocks[sec_idx];
        	sec_off_bytes = file->fd_pos % BLOCK_SIZE;
        	sec_left_bytes = BLOCK_SIZE - sec_off_bytes;
        	chunk_size = size_left < sec_left_bytes ? size_left : sec_left_bytes;
        	
            memset(io_buf,0,BLOCK_SIZE);
            ide_read(cur_part->my_disk,sec_lba,io_buf,1);
            memcpy(buf_dst,io_buf + sec_off_bytes,chunk_size);
            
            buf_dst += chunk_size;
            file->fd_pos += chunk_size;
            bytes_read += chunk_size;
            size_left -= chunk_size;
        }
        ASSERT(size_left == 0);
        sys_free(all_blocks);
        sys_free(io_buf);
        return bytes_read;
    }

--------------------

### 编写完的fs.c（sys\_read） ###

--------------------

int32_t sys_read(int32_t fd,void* buf,uint32_t count)
    { 
        if(fd < 0)
        { 
        	printk("sys_read: fd error\n");
        	return -1;
        }
        ASSERT(buf != NULL);
        uint32_t _fd = fd_local2global(fd);
        return file_read(&file_table[_fd],buf,count);
    }

--------------------

### 修改后的main.c ###

--------------------

#include "print.h"
    #include "init.h"
    #include "debug.h"
    #include "string.h"
    #include "memory.h"
    #include "../thread/thread.h"
    #include "interrupt.h"
    #include "../device/console.h"
    #include "../device/ioqueue.h"
    #include "../device/keyboard.h"
    #include "../userprog/process.h"
    #include "../lib/user/syscall.h"
    #include "../userprog/syscall-init.h"
    #include "../lib/stdio.h"
    #include "../lib/kernel/stdio-kernel.h"
    #include "../fs/fs.h"
    #include "../fs/file.h"
    
    int main(void) 
    { 
       put_str("I am kernel\n");
       init_all();
       intr_enable();
       char buf[64] = { 0};
       uint32_t fd = sys_open("/file1",O_CREAT);
       sys_close(fd);
       
       fd = sys_open("/file1",O_RDWR);
       printk("open /file1,fd:%d\n",fd);
       //sys_write(fd,"hello,world\n",12); //新硬盘可以先存数据用 要是之前存过删掉即可
       //sys_write(fd,"hello,world\n",12);
       sys_close(fd);
       
       fd = sys_open("/file1",O_RDONLY);
       int read_bytes = sys_read(fd,buf,18);
       printk("1_ read %d bytes:\n%s\n",read_bytes,buf);
       
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,7);
       printk("2_ read %d bytes:\n%s\n",read_bytes,buf);
       
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,2);
       printk("3_ read %d bytes:\n%s\n",read_bytes,buf);
       
       sys_close(fd);
       printk("________ close file1 and reopen ________\n");
       
       memset(buf,0,sizeof(buf));
       fd = sys_open("/file1",O_RDONLY);
       read_bytes = sys_read(fd,buf,24);
       printk("4_ read %d bytes:\n%s\n",read_bytes,buf);
       
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,1);
       printk("5_ read %d bytes:\n%s\n",read_bytes,buf);
       sys_close(fd);
       
       while(1);
       return 0;
    }

--------------------

### make all 验证成果 ###

--------------------

**因为要写博客 所以我就又重新复制了一个新的`hd80M.img` 为什么把新的给替换掉之前已经存入数据的`hd80M.img` 哈哈 因为这样最后实现效果看的更明显 那下面就看看实现起来是怎么样的**

**之前由于写入过两个`hello,world\n` 就直接用就行了 基本实现了哈**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTAwNTE2_size_16_color_FFFFFF_t_70]

--------------------

## 实现文件读写指针定位 ##

--------------------

**这部分还是挺简单的 哈哈 难得做这么简单的part 这部分part做了这一节就先完了 后面还有下一 下二 一节做两个part 最后一节3个part 安排各位看官看合理不合理 哈哈**

--------------------

### 编写后的fs.h（enum whence） ###

--------------------

enum whence
    { 
        SEEK_SET = 1,
        SEEK_CUR,
        SEEK_END
    };

--------------------

### 编写后的fs.c（sys\_lseek） ###

--------------------

int32_t sys_lseek(int32_t fd,int32_t offset,uint8_t whence)
    { 
        if(fd < 0)
        { 
            printk("sys_lseek: fd error\n");
            return -1;
        }
        ASSERT(whence > 0 && whence < 4);
        uint32_t _fd = fd_local2global(fd);
        struct file* file = &file_table[_fd];
        int32_t new_pos = 0;
        int32_t file_size = (int32_t)file->fd_inode->i_size;
        
        switch(whence)
        { 
            case SEEK_SET:
                new_pos = offset; //相对文件开始的偏移
                break;
            case SEEK_CUR:
                new_pos = offset + (int32_t)file->fd_pos;
                break;
            case SEEK_END:
                new_pos = offset + (int32_t)file_size;
                break;    
        }
        if(new_pos < 0 || new_pos > (file_size -1))
        	return -1;
       
        file->fd_pos = new_pos;
        return file->fd_pos;
    }

--------------------

### 编写后的main.c ###

--------------------

#include "print.h"
    #include "init.h"
    #include "debug.h"
    #include "string.h"
    #include "memory.h"
    #include "../thread/thread.h"
    #include "interrupt.h"
    #include "../device/console.h"
    #include "../device/ioqueue.h"
    #include "../device/keyboard.h"
    #include "../userprog/process.h"
    #include "../lib/user/syscall.h"
    #include "../userprog/syscall-init.h"
    #include "../lib/stdio.h"
    #include "../lib/kernel/stdio-kernel.h"
    #include "../fs/fs.h"
    #include "../fs/file.h"
    
    int main(void) 
    { 
       put_str("I am kernel\n");
       init_all();
       intr_enable();
       char buf[64] = { 0};
       uint32_t fd = sys_open("/file1",O_CREAT);
       sys_close(fd);
       
       fd = sys_open("/file1",O_RDWR);
       printk("open /file1,fd:%d\n",fd);
       //sys_write(fd,"hello,world\n",12); //新硬盘可以先存数据用 要是之前存过删掉即可
       //sys_write(fd,"hello,world\n",12);
       sys_close(fd);
       
       fd = sys_open("/file1",O_RDONLY);
       int read_bytes = sys_read(fd,buf,18);
       printk("1_ read %d bytes:\n%s\n",read_bytes,buf);
       
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,7);
       printk("2_ read %d bytes:\n%s",read_bytes,buf);
       
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,2);
       printk("3_ read %d bytes:\n%s",read_bytes,buf);
       
       printk("________ SEEK_SET 0 ________\n");
       
       sys_lseek(fd,0,SEEK_SET);
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,25);
       printk("4_ read %d bytes:\n%s",read_bytes,buf);
       
       printk("________ SEEK_SET 6 ________\n");
       sys_lseek(fd,6,SEEK_SET);
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,5);
       printk("5_ read %d bytes:\n%s\n",read_bytes,buf);
       
       printk("________ SEEK_CUR 1________\n");
       sys_lseek(fd,1,SEEK_CUR);
       memset(buf,0,sizeof(buf));
       read_bytes = sys_read(fd,buf,5);
       printk("6_ read %d bytes:\n%s",read_bytes,buf);
       
       while(1);
       return 0;
    }

--------------------

### make all 验证成果 ###

--------------------

**偏移了多次 且调用了`SEEK_CUR`和`SEEK_SET`**  
**看效果应该是对的哈哈 那各位看官下一篇再见~**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTAwNTE2_size_16_color_FFFFFF_t_70 1]

[Link 1]: https://love6.blog.csdn.net/article/details/119133589
[lseek]: https://blog.csdn.net/qq_40082488/article/details/116738175
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTAwNTE2_size_16_color_FFFFFF_t_70]: /images/20220829/1ddba20cdcd84872aedf1014d1f64121.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NTAwNTE2_size_16_color_FFFFFF_t_70 1]: /images/20220829/58d42c2f223740c28d686238c67617ff.png