嵌入式Linux 设置时间和日期 API ，它是busybox要提取的源代码。

Linux设置时间和日期的步骤：

1. 设置系统时间和日期；

2. 该系统的时间和日期，同步到硬件。

#include <stdio.h>

#include <fcntl.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <sys/ioctl.h>

#include <time.h>

#include <linux/rtc.h>

#include <linux/capability.h> 

int  SetSysDateAndTime(const char *time_str);

void SetHWClockFromSysClock(int utc);

static int  rtc_xopen(const char **default_rtc, int flags);

static void write_rtc(time_t t, int utc);

static const char *rtcname;

int main(void)

{

	const char time_str[] = "1989-11-22 11:22:33";

	SetSysDateAndTime(time_str);

	SetHWClockFromSysClock(0);

	system("reboot");

	return 0;

}

int SetSysDateAndTime(const char *time_str)

{

    struct tm 			time_tm;

    struct timeval 	time_tv;

    time_t 					timep;

		int 						ret;

		if(time_str == NULL)

		{

				fprintf(stderr, "time string args invalid!\n");

				return -1;

		}

    sscanf(time_str, "%d-%d-%d %d:%d:%d", &time_tm.tm_year, &time_tm.tm_mon, &time_tm.tm_mday, &time_tm.tm_hour, &time_tm.tm_min, &time_tm.tm_sec);

    time_tm.tm_year 	-= 1900;

    time_tm.tm_mon 		-= 1;

    time_tm.tm_wday 	= 0;

    time_tm.tm_yday 	= 0;

    time_tm.tm_isdst	= 0;

    timep = mktime(&time_tm);

    time_tv.tv_sec  = timep;

    time_tv.tv_usec = 0;

    ret = settimeofday(&time_tv, NULL);

    if(ret != 0)

    {

        fprintf(stderr, "settimeofday failed\n");

        return -2;

    }

	return 0;

}

void SetHWClockFromSysClock(int utc)

{

	struct timeval tv;

	gettimeofday(&tv, NULL);

	//if (gettimeofday(&tv, NULL))

	//	bb_perror_msg_and_die("gettimeofday() failed");

	write_rtc(tv.tv_sec, utc);

}

static int  rtc_xopen(const char **default_rtc, int flags)

{

	int rtc;

	if (!*default_rtc) {

		*default_rtc = "/dev/rtc";

		rtc = open(*default_rtc, flags);

		if (rtc >= 0)

			return rtc;

		*default_rtc = "/dev/rtc0";

		rtc = open(*default_rtc, flags);

		if (rtc >= 0)

			return rtc;

		*default_rtc = "/dev/misc/rtc";

	}

	return open(*default_rtc, flags);

}

static void write_rtc(time_t t, int utc)

{

#define RTC_SET_TIME	_IOW('p', 0x0a, struct rtc_time) /* Set RTC time    */

	struct tm tm;

	int rtc = rtc_xopen(&rtcname, O_WRONLY);

	tm = *(utc ?

gmtime(&t) : localtime(&t));

	tm.tm_isdst = 0;

	ioctl(rtc, RTC_SET_TIME, &tm);

	close(rtc);

}