Linux kernel內讀寫檔案

在driver裡面，我們有時需要留一些資訊在磁碟上讓userspace作溝通，因此需要從kernel上直接寫入檔案。

相關API程式碼如下：

void InitKernelEnv(void){ 
   oldfs = get_fs(); 
   set_fs(KERNEL_DS); 
} 

void DinitKernelEnv(){
   set_fs(oldfs); 
}

struct file *OpenFile(char *path,int flag,int mode){ 
   struct file *fp; 
    
   fp=filp_open(path, flag, 0); 
   if (fp) return fp; 
   else return NULL; 
}

int WriteFile(struct file *fp,char *buf,int readlen) { 
   if (fp->f_op && fp->f_op->read) 
      return fp->f_op->write(fp,buf,readlen, &fp->f_pos); 
   else 
      return -1; 
} 

int ReadFile(struct file *fp,char *buf,int readlen) 
{ 
   if (fp->f_op && fp->f_op->read) 
      return fp->f_op->read(fp,buf,readlen, &fp->f_pos); 
   else 
      return -1; 
} 

int CloseFile(struct file *fp) { 
   filp_close(fp,NULL); 
   return 0; 
}

而使用方法請參考下面這個範例：

void test(){
   char read_buf[2048] = "";
   char write_buf[2048] = "";
   struct file *fp; 

   InitKernelEnv(); 
   
   //read file
   fp = OpenFile(WPS_STA_LIST_FILE, O_RDONLY | O_CREAT, 0); 
   if(fp != NULL){ 
         ReadFile(fp, read_buf, sizeof(read_buf));
   }

   CloseFile(fp); 
   

   //write to file
   fp = OpenFile(WPS_STA_LIST_FILE, O_CREAT | O_WRONLY, 0); 
   if (fp!= NULL) { 
      WriteFile(fp, write_buf, sizeof(write_buf));
   }

   CloseFile(fp); 
   
   DinitKernelEnv();

}

參考資料：
[1] 請問內核中讀寫配置文件的源碼在哪個目錄的哪個文件中
[2] Reading file in kernel-簡單但實用