[LTP] [PATCH v4 17/31] testcases: sysfs: Add sys_rtc01
Cyril Hrubis
chrubis@suse.cz
Thu Aug 27 13:21:43 CEST 2026
A test for /sys/class/rtc/*/* files.
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
include/tst_path_defs.h | 1 +
runtest/sysfs | 1 +
testcases/kernel/sysfs/class/rtc/.gitignore | 1 +
testcases/kernel/sysfs/class/rtc/Makefile | 7 +
testcases/kernel/sysfs/class/rtc/sys_rtc01.c | 259 +++++++++++++++++++
5 files changed, 269 insertions(+)
create mode 100644 testcases/kernel/sysfs/class/rtc/.gitignore
create mode 100644 testcases/kernel/sysfs/class/rtc/Makefile
create mode 100644 testcases/kernel/sysfs/class/rtc/sys_rtc01.c
diff --git a/include/tst_path_defs.h b/include/tst_path_defs.h
index 425300f0c..4c3921da0 100644
--- a/include/tst_path_defs.h
+++ b/include/tst_path_defs.h
@@ -97,6 +97,7 @@
#define PATH_CLASS_BDI "/sys/class/bdi"
#define PATH_CLASS_HWMON "/sys/class/hwmon"
#define PATH_CLASS_LEDS "/sys/class/leds"
+#define PATH_CLASS_RTC "/sys/class/rtc"
#define PATH_CLASS_WAKEUP "/sys/class/wakeup"
/* SYSFS DEVICES */
diff --git a/runtest/sysfs b/runtest/sysfs
index b8d003228..de58499be 100644
--- a/runtest/sysfs
+++ b/runtest/sysfs
@@ -13,3 +13,4 @@ sys_bdi01 sys_bdi01
sys_hwmon01 sys_hwmon01
sys_leds01 sys_leds01
sys_wakeup01 sys_wakeup01
+sys_rtc01 sys_rtc01
diff --git a/testcases/kernel/sysfs/class/rtc/.gitignore b/testcases/kernel/sysfs/class/rtc/.gitignore
new file mode 100644
index 000000000..0ce416b43
--- /dev/null
+++ b/testcases/kernel/sysfs/class/rtc/.gitignore
@@ -0,0 +1 @@
+/sys_rtc01
diff --git a/testcases/kernel/sysfs/class/rtc/Makefile b/testcases/kernel/sysfs/class/rtc/Makefile
new file mode 100644
index 000000000..034038061
--- /dev/null
+++ b/testcases/kernel/sysfs/class/rtc/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2026 Cyril Hrubis <chrubis@suse.cz>
+
+top_srcdir ?= ../../../../..
+
+include $(top_srcdir)/include/mk/testcases.mk
+include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/kernel/sysfs/class/rtc/sys_rtc01.c b/testcases/kernel/sysfs/class/rtc/sys_rtc01.c
new file mode 100644
index 000000000..89141f2fa
--- /dev/null
+++ b/testcases/kernel/sysfs/class/rtc/sys_rtc01.c
@@ -0,0 +1,259 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+/*\
+ * Sanity checks for the RTC attributes exported under
+ * /sys/class/rtc/rtcN/.
+ *
+ * date and time report the RTC clock in UTC, while since_epoch reports the
+ * same value pre-converted to a Unix timestamp. For every RTC device the
+ * test verifies that:
+ *
+ * - hctosys is a boolean
+ * - max_user_freq is greater than zero
+ * - since_epoch matches date and time converted to a Unix timestamp
+ * - for the RTC device with hctosys == 1, i.e. the one that was actually
+ * used by the kernel's own CONFIG_RTC_HCTOSYS code to set the system clock
+ * at boot, since_epoch is additionally close to the current system time(2)
+ * value. On a system with multiple RTC devices the other ones are not
+ * guaranteed to be in sync with the system clock at all (e.g. a
+ * peripheral's battery-backed RTC used only for its own wakeup alarm), so
+ * this second check is skipped for them.
+ *
+ * The hctosys only reflects whether the kernel itself performed the sync;
+ * many setups runs ``hwclock --hctosys`` from a userspace init script instead
+ * to sync the system clock from the RTC without the kernel ever knowing
+ * about it, leaving hctosys == 0 on every device despite the clock
+ * legitimately being in sync. To still get coverage on such systems, if no
+ * RTC has hctosys == 1 at all, rtc0 is treated as the presumed primary RTC
+ * and gets the system time check anyway.
+ *
+ * The date/time vs since_epoch cross-check allows a few seconds of slack since
+ * they are read from separate files and the wall clock keeps ticking in
+ * between reads. The code also checks for midnight rollover and re-reads the
+ * values if that happens.
+ *
+ * The since_epoch vs system time(2) cross-check allows extra slack that
+ * grows with system uptime: the RTC is a free-running hardware crystal
+ * oscillator that (absent some periodic resync mechanism, which is not
+ * guaranteed to be running) drifts independently of the system clock the
+ * whole time the system is up, not just across the couple of reads this
+ * test performs, so on a long-running system a purely fixed slack would
+ * eventually produce false failures even on perfectly healthy hardware.
+ *
+ * The check may still fail if the system was booted with RTC that is fairly
+ * off the current time and the system was later synced with NTP. This is out
+ * of scope of this test.
+ *
+ * Under virtualization the slack is additionally multiplied, since a VM's
+ * clock (and thus its emulated RTC) commonly lags real time by tens of
+ * seconds right after boot due to hypervisor scheduling delays (steal time)
+ * during the guest's own boot sequence, which is unrelated to physical RTC
+ * crystal drift and not scaled away by the uptime-based slack above.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <dirent.h>
+#include <limits.h>
+#include <time.h>
+#include <sys/sysinfo.h>
+#include "tst_test.h"
+#include "tst_sysfs_assert.h"
+#include "tst_path_defs.h"
+
+#define SLACK_SEC 10
+
+/*
+ * Generously high assumed worst-case RTC crystal drift, in parts per
+ * million, used to scale the system time slack with uptime. 200 ppm covers
+ * even fairly poor/uncompensated RTC crystals across a wide temperature
+ * range; a decent RTC typically drifts far less than this.
+ */
+#define MAX_RTC_DRIFT_PPM 200
+
+/*
+ * VM guest clocks commonly lag behind real time by tens of seconds right
+ * after boot due to hypervisor steal time accumulated during the guest's
+ * own boot sequence, see the top comment. This is unrelated to physical RTC
+ * crystal drift, hence a flat multiplier here rather than folding it into
+ * MAX_RTC_DRIFT_PPM's uptime-based scaling.
+ */
+#define VIRT_SLACK_MULTIPLIER 10
+
+static long sys_time_slack_sec(void)
+{
+ struct sysinfo info;
+ long slack;
+
+ SAFE_SYSINFO(&info);
+
+ slack = SLACK_SEC + (long)info.uptime * MAX_RTC_DRIFT_PPM / 1000000;
+
+ if (tst_is_virt(VIRT_ANY)) {
+ tst_res(TINFO,
+ "Running in a VM, multiplying the RTC vs system time slack by %d",
+ VIRT_SLACK_MULTIPLIER);
+ slack *= VIRT_SLACK_MULTIPLIER;
+ }
+
+ return slack;
+}
+
+static long read_hctosys(const char *name)
+{
+ return TST_SYSFS_READ_LI(PATH_CLASS_RTC "/%s/hctosys", name);
+}
+
+static void read_rtc_snapshot(const char *name, char *date, size_t date_size,
+ char *rtc_time, size_t time_size,
+ time_t *since_epoch)
+{
+ char date2[32];
+ int i;
+
+ /*
+ * Retry if the date changed between the reads -> midnight rollover
+ * happened.
+ */
+ for (i = 0; i < 2; i++) {
+ TST_SYSFS_READ_STR(date, date_size, PATH_CLASS_RTC "/%s/date", name);
+ TST_SYSFS_READ_STR(rtc_time, time_size, PATH_CLASS_RTC "/%s/time",
+ name);
+
+ *since_epoch = TST_SYSFS_READ_LI(PATH_CLASS_RTC "/%s/since_epoch", name);
+
+ TST_SYSFS_READ_STR(date2, sizeof(date2), PATH_CLASS_RTC "/%s/date",
+ name);
+
+ if (!strcmp(date, date2))
+ return;
+
+ tst_res(TINFO,
+ "%s: date rolled over mid-read (%s -> %s), retrying",
+ name, date, date2);
+ }
+
+ tst_res(TWARN, "%s: date kept rolling over across the retry", name);
+}
+
+static void check_rtc(const char *name, int any_hctosys)
+{
+ char date[32] = "", rtc_time[32] = "";
+ struct tm tm = { 0 };
+ time_t rtc_epoch, sys_epoch;
+ long hctosys, slack;
+ time_t since_epoch;
+ int is_primary;
+
+ TST_SYSFS_ASSERT_BOOL(PATH_CLASS_RTC "/%s/hctosys", name);
+ TST_SYSFS_ASSERT_RANGELL(1, LONG_MAX, PATH_CLASS_RTC "/%s/max_user_freq", name);
+
+ hctosys = read_hctosys(name);
+
+ /*
+ * If no RTC has hctosys == 1 anywhere (see the top comment), fall
+ * back to treating rtc0 as the presumed primary RTC.
+ */
+ is_primary = hctosys || (!any_hctosys && !strcmp(name, "rtc0"));
+
+ read_rtc_snapshot(name, date, sizeof(date), rtc_time, sizeof(rtc_time),
+ &since_epoch);
+
+ sys_epoch = time(NULL);
+
+ if (sscanf(date, "%d-%d-%d", &tm.tm_year, &tm.tm_mon, &tm.tm_mday) != 3 ||
+ sscanf(rtc_time, "%d:%d:%d", &tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 3) {
+ tst_res(TFAIL, "%s: failed to parse date '%s' / time '%s'",
+ name, date, rtc_time);
+ return;
+ }
+
+ tm.tm_year -= 1900;
+ tm.tm_mon -= 1;
+ rtc_epoch = timegm(&tm);
+
+ if (llabs((long long)(rtc_epoch - since_epoch)) <= SLACK_SEC) {
+ tst_res(TPASS,
+ "%s: since_epoch (%lld) matches date '%s' time '%s' (%lld)",
+ name, (long long)since_epoch, date, rtc_time,
+ (long long)rtc_epoch);
+ } else {
+ tst_res(TFAIL,
+ "%s: since_epoch (%lld) does not match date '%s' time '%s' (%lld)",
+ name, (long long)since_epoch, date, rtc_time,
+ (long long)rtc_epoch);
+ }
+
+ if (!is_primary) {
+ tst_res(TINFO,
+ "%s: not the (assumed) primary RTC, not checking since_epoch against system time",
+ name);
+ return;
+ }
+
+ slack = sys_time_slack_sec();
+ long long diff = llabs((long long)(since_epoch - sys_epoch));
+
+ if (diff <= slack) {
+ tst_res(TPASS,
+ "%s: since_epoch (%lld), system time (%lld), diff %llds <= slack %lds",
+ name, (long long)since_epoch, (long long)sys_epoch,
+ diff, slack);
+ } else {
+ tst_res(TFAIL,
+ "%s: since_epoch (%lld), system time (%lld), diff %llds > slack %lds",
+ name, (long long)since_epoch, (long long)sys_epoch,
+ diff, slack);
+ }
+}
+
+static void do_test(void)
+{
+ DIR *d;
+ struct dirent *ent;
+ int found = 0;
+ int any_hctosys = 0;
+
+ if (!tst_sysfs_exists(PATH_CLASS_RTC))
+ tst_brk(TCONF, PATH_CLASS_RTC ": not present");
+
+ d = SAFE_OPENDIR(PATH_CLASS_RTC);
+
+ /* First pass: find out whether any RTC has hctosys == 1 already. */
+ while ((ent = SAFE_READDIR(d))) {
+ if (strncmp(ent->d_name, "rtc", 3))
+ continue;
+
+ found = 1;
+
+ if (read_hctosys(ent->d_name))
+ any_hctosys = 1;
+ }
+
+ if (!found) {
+ tst_res(TCONF, "No RTC device found");
+ SAFE_CLOSEDIR(d);
+ return;
+ }
+
+ rewinddir(d);
+
+ /* Second pass: run the actual checks. */
+ while ((ent = SAFE_READDIR(d))) {
+ if (strncmp(ent->d_name, "rtc", 3))
+ continue;
+
+ tst_res(TINFO, "Checking %s", ent->d_name);
+ check_rtc(ent->d_name, any_hctosys);
+ }
+
+ SAFE_CLOSEDIR(d);
+}
+
+static struct tst_test test = {
+ .test_all = do_test,
+};
--
2.54.0
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