linux內核原代碼init/main的注釋
 

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第八軍團 時間：2004-1-23 15:49:05 
   
#define __LIBRARY__
　　#include 
　　#include 
　　/*
　　* 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) @@定義fork
　　--sys_fork在unistd.h中定義syscall0
　　static inline _syscall0(int,pause)
　　static inline _syscall0(int,setup)
　　static inline _syscall0(int,sync) 
#include 
　　#include 
　　#include 
　　#include 
　　#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) ({ \
　　outb_p(0x80|addr,0x70); \
　　inb_p(0x71); \
　　}) 

#define BCD_TO_BIN(val) ((val)=((val)&15) + ((val)>>4)*10) 

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));
　　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(); @@切至用戶模式???到哪去了,回來了!!!
　　if (!fork()) { /* we count on this going ok */
　　 init(); @@fork在unistd.h有其宏擴展int 0x80　
　　 如何返回兩次?應該說子進程如何激活?
　　}
　　/*
　　* 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();
　　 @@pause 同fork在unistd.h有其宏擴展int 0x80 然后調schedule()
　　} 

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(); @@系統0號調用
　　if (!fork())
　　 _exit(execve("/bin/update",NULL,NULL));
　　(void) open("/dev/tty0",O_RDWR,0); @@打開控制臺
　　(void) dup(0); @@復制
　　(void) dup(0);
　　printf("%d buffers = %d bytes buffer space\n\r",NR_BUFFERS,
　　 NR_BUFFERS*BLOCK_SIZE);
　　printf(" Ok.\n\r");
　　if ((i=fork())<0)
　　 printf("Fork failed in init\r\n");
　　else if (!i) { @@啟動一root shell進程?
　　 close(0);close(1);close(2);
　　 setsid();
　　 (void) open("/dev/tty0",O_RDWR,0);
　　 (void) dup(0);
　　 (void) dup(0);
　　 _exit(execve("/bin/sh",argv,envp));
　　}
　　j=wait(&i);
　　printf("child %d died with code %04x\n",j,i);
　　sync();
　　_exit(0); /* NOTE! _exit, not exit() */
　　}