efi_time.c

#include "efi_time.h"
#include <time.h>

char *
efi_strptime(const char *s, const char *format, efi_time_t *time)
{
	struct tm tm;
	char *end;

	if (!s || !format || !time) {
		errno = EINVAL;
		return NULL;
	}

	tzset();

	memset(&tm, 0, sizeof(tm));
	end = strptime(s, format, &tm);
	if (end == NULL)
		return NULL;

	time->pad2 = 0;
	time->daylight = tm.tm_isdst ? EFI_TIME_IN_DAYLIGHT : 0;
	time->timezone = timezone / 60;
	time->nanosecond = 0;
	time->pad1 = 0;
	time->second = tm.tm_sec;
	time->minute = tm.tm_min;
	time->hour = tm.tm_hour;
	time->day = tm.tm_mday;
	time->month = tm.tm_mon + 1;
	time->year = tm.tm_year + 1900;

	return end;
}

size_t
efi_strftime(char *s, size_t max, const char *format, const efi_time_t *time)
{
	size_t ret = 0;
	struct tm tm = { 0 };
	char *oldtz, *tz = NULL;

	if (!s || !format || !time) {
		errno = EINVAL;
		return ret;
	}

	oldtz = strdupa(secure_getenv("TZ"));

	if (time->timezone == EFI_UNSPECIFIED_TIMEZONE) {
		unsetenv("TZ");
	} else {
		char tzsign = time->timezone >= 0 ? '+' : '-';
		int tzabs = tzsign == '+' ? time->timezone : -time->timezone;
		int16_t tzhours = tzabs / 60;
		int16_t tzminutes = tzabs % 60;

		/*
		 * I have no idea what the right thing to do with DST is
		 * here, so I'm going to ignore it.
		 */
		asprintfa(&tz, "UTC%c%"PRId16":%"PRId16":00",
			  tzsign, tzhours, tzminutes);
		setenv("TZ", tz, 1);
	}
	tzset();

	tm.tm_year = time->year - 1900;
	tm.tm_mon = time->month - 1;
	tm.tm_mday = time->day;
	tm.tm_hour = time->hour;
	tm.tm_min = time->minute;
	tm.tm_sec = time->second;
	tm.tm_isdst = (time->daylight & EFI_TIME_IN_DAYLIGHT) ? 1 : 0;

	ret = strftime(s, max, format, &tm);
	if (oldtz)
		setenv("TZ", oldtz, 1);
	else
		unsetenv("TZ");
	return ret;
}

// vim:fenc=utf-8:tw=75:noet

efi_time.h

typedef struct {
        uint16_t        year;           // 1900 - 9999
        uint8_t         month;          // 1 - 12
        uint8_t         day;            // 1 - 31
        uint8_t         hour;           // 0 - 23
        uint8_t         minute;         // 0 - 59
        uint8_t         second;         // 0 - 59 // ha ha only serious
        uint8_t         pad1;           // 0
        uint32_t        nanosecond;     // 0 - 999,999,999
        int16_t         timezone;       // minutes from UTC or EFI_UNSPECIFIED_TIMEZONE
        uint8_t         daylight;       // bitfield
        uint8_t         pad2;           // 0
} efi_time_t __attribute__((__aligned__(1)));

#define EFI_TIME_ADJUST_DAYLIGHT        ((uint8_t)0x01)
#define EFI_TIME_IN_DAYLIGHT            ((uint8_t)0x02)

#define EFI_UNSPECIFIED_TIMEZONE        ((uint16_t)0x07ff)