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() */
}