+static ssize_t
+rtc_sysfs_set_wakealarm(struct device *dev, struct device_attribute *attr,
+ const char *buf, size_t n)
+{
+ ssize_t retval;
+ unsigned long now, alarm;
+ struct rtc_wkalrm alm;
+ struct rtc_device *rtc = to_rtc_device(dev);
+ char *buf_ptr;
+ int adjust = 0;
+
+ /* Only request alarms that trigger in the future. Disable them
+ * by writing another time, e.g. 0 meaning Jan 1 1970 UTC.
+ */
+ retval = rtc_read_time(rtc, &alm.time);
+ if (retval < 0)
+ return retval;
+ rtc_tm_to_time(&alm.time, &now);
+
+ buf_ptr = (char *)buf;
+ if (*buf_ptr == '+') {
+ buf_ptr++;
+ adjust = 1;
+ }
+ alarm = simple_strtoul(buf_ptr, NULL, 0);
+ if (adjust) {
+ alarm += now;
+ }
+ if (alarm > now) {
+ /* Avoid accidentally clobbering active alarms; we can't
+ * entirely prevent that here, without even the minimal
+ * locking from the /dev/rtcN api.
+ */
+ retval = rtc_read_alarm(rtc, &alm);
+ if (retval < 0)
+ return retval;
+ if (alm.enabled)
+ return -EBUSY;
+
+ alm.enabled = 1;
+ } else {
+ alm.enabled = 0;
+
+ /* Provide a valid future alarm time. Linux isn't EFI,
+ * this time won't be ignored when disabling the alarm.
+ */
+ alarm = now + 300;
+ }
+ rtc_time_to_tm(alarm, &alm.time);
+
+ retval = rtc_set_alarm(rtc, &alm);
+ return (retval < 0) ? retval : n;
+}
+static DEVICE_ATTR(wakealarm, S_IRUGO | S_IWUSR,
+ rtc_sysfs_show_wakealarm, rtc_sysfs_set_wakealarm);