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) @@定义fork
　　 --sys_fork在unistd.h中定义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(); @@切至用户模式???到哪去了,回来了!!!
　　 if (!fork()) { /* we count on this going ok */
　　 init(); @@fork在unistd.h有其宏扩展int 0x80　
　　 如何返回两次?应该说子进程如何激活?
　　 }
　　 /*
　　 * 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有其宏扩展int 0x80 然后调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(); @@系统0号调用
　　 if (!fork())
　　 _exit(execve("/bin/update",NULL,NULL));
　　 (void) open("/dev/tty0",O_RDWR,0); @@打开控制台
　　 (void) dup(0); @@复制
　　 (void) dup(0);
　　 printf("%d buffers = %d bytes buffer spacenr",NR_BUFFERS,
　　 NR_BUFFERS*BLOCK_SIZE);
　　 printf(" Ok.nr");
　　 if ((i=fork())<0)
　　 printf("Fork failed in initrn");
　　 else if (!i) { @@启动一root shell进程?
　　 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 %04xn",j,i);
　　 sync();
　　 _exit(0); /* NOTE! _exit, not exit() */
　　 }