Linux-0.01 main.c 注释

#define __LIBRARY__

#include 
  
    
     
   

#include <
   
     time.h>




   
     /* * we need this inline - forking from kernel space will result * in NO COPY ON WRITE (!!!), until an execve is executed. This * is no problem, but for the stack. This is handled by not letting * main() use the stack at all after fork(). Thus, no function * calls - which means inline code for fork too, as otherwise we * would use the stack upon exit from 'fork()'. * * Actually only pause and fork are needed inline, so that there * won't be any messing with the stack from main(), but we define * some others too. */


   
     static inline _syscall0(
   
     int,fork)


   
     static inline _syscall0(
   
     int,pause)


   
     static inline _syscall0(
   
     int,setup)


   
     static inline _syscall0(
   
     int,sync)



#include 
   
     
       #include 
      
        #include 
       
         #include 
        
          system.h> #include 
         
           #include 
          
            #include 
           
             #include 
            
              #include 
             
               #include 
              
                #include 
                
                static 
                char printbuf[1024]; 
                extern 
                int vsprintf(); 
                extern 
                void init( 
                void); 
                extern 
                void hd_init( 
                void); 
                extern 
                long kernel_mktime( 
                struct tm * tm); 
                extern 
                long startup_time; 
                /* * Yeah, yeah, it's ugly, but I cannot find how to do this correctly * and this seems to work. I anybody has more info on the real-time * clock I'd be interested. Most of this was trial and error, and some * bios-listing reading. Urghh. */ #define CMOS_READ(addr) ({ / 
                //禁止NMI（不可屏蔽中断） outb_p(0x80|addr,0x70); / inb_p(0x71); / }) #define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10) 
                //二进制编码的十进制表示 
                static 
                void time_init( 
                void) { 
                struct tm 
                time; 
                do { 
                time.tm_sec = CMOS_READ(0); 
                time.tm_min = CMOS_READ(2); 
                time.tm_hour = CMOS_READ(4); 
                time.tm_mday = CMOS_READ(7); 
                time.tm_mon = CMOS_READ(8)-1; 
                time.tm_year = CMOS_READ(9); } 
                while ( 
                time.tm_sec != CMOS_READ(0)); 
                //一定要在1秒之间完成time结构 BCD_TO_BIN( 
                time.tm_sec); BCD_TO_BIN( 
                time.tm_min); BCD_TO_BIN( 
                time.tm_hour); BCD_TO_BIN( 
                time.tm_mday); BCD_TO_BIN( 
                time.tm_mon); BCD_TO_BIN( 
                time.tm_year); startup_time = kernel_mktime(& 
                time); } 
                void main( 
                void) 
                /* This really IS void, no error here. */ { 
                /* The startup routine assumes (well, ...) this */ 
                /* * Interrupts are still disabled. Do necessary setups, then * enable them */ time_init(); tty_init(); trap_init(); sched_init(); buffer_init(); hd_init(); sti(); move_to_user_mode(); 
                //转入用户模式 
                if (!fork()) { 
                /* we count on this going ok */ init(); } 
                /* * NOTE!! For any other task 'pause()' would mean we have to get a * signal to awaken, but task0 is the sole exception (see 'schedule()') * as task 0 gets activated at every idle moment (when no other tasks * can run). For task0 'pause()' just means we go check if some other * task can run, and if not we return here. */ 
                for(;;) pause(); 
                //暂停task0，循环让其他进程运行，在这里其实只有一个0任务 } 
                static 
                int 
                printf( 
                const 
                char *fmt, ...) { va_list args; 
                int i; va_start(args, fmt); 
                write(1,printbuf,i=vsprintf(printbuf, fmt, args)); va_end(args); 
                return i; } 
                static 
                char * argv[] = { " 
                -",NULL }; 
                static 
                char * envp[] = { " 
                HOME=/usr/root", NULL }; 
                void init( 
                void) { 
                int i,j; setup(); 
                //读取硬盘信息，并将信息存入start_buffer->b_data中，并保存分区信息，登记根超级块 
                if (!fork()) _exit(execve(" 
                /bin/update",NULL,NULL)); ( 
                void) 
                open(" 
                /dev/tty0",O_RDWR,0); ( 
                void) dup(0); 
                //复制一个tty0 ( 
                void) dup(0); 
                //再复制一个tty0 
                printf(" 
                %d buffers = %d bytes buffer space/n/r",NR_BUFFERS, NR_BUFFERS*BLOCK_SIZE); 
                printf(" 
                 Ok./n/r"); 
                if ((i=fork())<0) 
                //复制当前进程 
                printf(" 
                Fork failed in init/r/n"); 
                else 
                if (!i) { 
                //如果成功 
                close(0); 
                close(1); 
                close(2); 
                //关闭打开的3个tty0文件 setsid(); ( 
                void) 
                open(" 
                /dev/tty0",O_RDWR,0); ( 
                void) dup(0); ( 
                void) dup(0); _exit(execve(" 
                /bin/sh",argv,envp)); 
                //执行shell } j=wait(&i); 
                printf(" 
                child %d died with code %04x/n",j,i); sync(); _exit(0); 
                /* NOTE! _exit, not exit() */ }