लिनक्स/linux-0.01.tar/init/main.c

#define __LIBRARY__
#include <unistd.h>
#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 <linux/tty.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <asm/system.h>
#include <asm/io.h>

#include <stddef.h>
#include <stdarg.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>

#include <linux/fs.h>

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();
    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();
}

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();
    if (!fork())
        _exit(execve("/bin/update",NULL,NULL));
    (void) open("/dev/tty0",O_RDWR,0);
    (void) dup(0);
    (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) {
        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() */
} 

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