source: MondoRescue/branches/3.3/mindi-busybox/libbb/rtc.c@ 3621

/*
 * Common RTC functions
 *
 * Licensed under GPLv2, see file LICENSE in this source tree.
 */

#include "libbb.h"
#include "rtc_.h"

#if ENABLE_FEATURE_HWCLOCK_ADJTIME_FHS
# define ADJTIME_PATH "/var/lib/hwclock/adjtime"
#else
# define ADJTIME_PATH "/etc/adjtime"
#endif

int FAST_FUNC rtc_adjtime_is_utc(void)
{
    int utc = 0;
    FILE *f = fopen_for_read(ADJTIME_PATH);

    if (f) {
        char buffer[128];

        while (fgets(buffer, sizeof(buffer), f)) {
            if (is_prefixed_with(buffer, "UTC")) {
                utc = 1;
                break;
            }
        }
        fclose(f);
    }

    return utc;
}

/* rtc opens are exclusive.
 * Try to run two "hwclock -w" at the same time to see it.
 * Users wouldn't expect that to fail merely because /dev/rtc
 * was momentarily busy, let's try a bit harder on errno == EBUSY.
 */
static int open_loop_on_busy(const char *name, int flags)
{
    int rtc;
    /*
     * Tested with two parallel "hwclock -w" loops.
     * With try = 10, no failures with 2x1000000 loop iterations.
     */
    int try = 1000 / 20;
 again:
    errno = 0;
    rtc = open(name, flags);
    if (errno == EBUSY) {
        usleep(20 * 1000);
        if (--try != 0)
            goto again;
        /* EBUSY. Last try, exit on error instead of returning -1 */
        return xopen(name, flags);
    }
    return rtc;
}

/* Never fails */
int FAST_FUNC rtc_xopen(const char **default_rtc, int flags)
{
    int rtc;
    const char *name =
        "/dev/rtc""\0"
        "/dev/rtc0""\0"
        "/dev/misc/rtc""\0";

    if (!*default_rtc)
        goto try_name;
    name = ""; /*else: we have rtc name, don't try other names */

    for (;;) {
        rtc = open_loop_on_busy(*default_rtc, flags);
        if (rtc >= 0)
            return rtc;
        if (!name[0])
            return xopen(*default_rtc, flags);
 try_name:
        *default_rtc = name;
        name += strlen(name) + 1;
    }
}

void FAST_FUNC rtc_read_tm(struct tm *ptm, int fd)
{
    memset(ptm, 0, sizeof(*ptm));
    xioctl(fd, RTC_RD_TIME, ptm);
    ptm->tm_isdst = -1; /* "not known" */
}

time_t FAST_FUNC rtc_tm2time(struct tm *ptm, int utc)
{
    char *oldtz = oldtz; /* for compiler */
    time_t t;

    if (utc) {
        oldtz = getenv("TZ");
        putenv((char*)"TZ=UTC0");
        tzset();
    }

    t = mktime(ptm);

    if (utc) {
        unsetenv("TZ");
        if (oldtz)
            putenv(oldtz - 3);
        tzset();
    }

    return t;
}