From: Noé Rubinstein <noe.rubinstein@xxxxxxxxx>
This option is useful for systems that have a working hardware clock, but do
not provide a way to write to it. Instead of setting the hardware clock, write
the difference between hardware and system clock to a file; when getting the
hardware clock, add the offset from this file to obtain the correct time.
I have not checked how well this interacts with the adjtime mechanism, so
this is an RFC patch.
---
sys-utils/hwclock.8.in | 6 ++++
sys-utils/hwclock.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 92 insertions(+), 2 deletions(-)
diff --git a/sys-utils/hwclock.8.in b/sys-utils/hwclock.8.in
index b11b45c..63fabda 100644
--- a/sys-utils/hwclock.8.in
+++ b/sys-utils/hwclock.8.in
@@ -113,6 +113,12 @@ not reset.
.BR \-w , \ \-\-systohc
Set the Hardware Clock to the current System Time.
.TP
+.BR \-\-offset[=filename]
+This option is useful for systems that have a working hardware clock, but do
+not provide a way to write to it. Instead of setting the hardware clock, write
+the difference between hardware and system clock to a file; when getting the
+hardware clock, add the offset from this file to obtain the correct time.
+.TP
.BR \-V , \ \-\-version
Display version information and exit.
.TP
diff --git a/sys-utils/hwclock.c b/sys-utils/hwclock.c
index e780158..c7deab9 100644
--- a/sys-utils/hwclock.c
+++ b/sys-utils/hwclock.c
@@ -98,6 +98,7 @@ struct clock_ops *ur;
#define MAX_DRIFT 2145.0
const char *adj_file_name = NULL;
+const char *offset_file_name = NULL;
struct adjtime {
/*
@@ -234,6 +235,35 @@ hw_clock_is_utc(const bool utc, const bool local_opt,
return ret;
}
+static int read_offset(struct timeval *offset)
+{
+ FILE *f;
+ int rc;
+ f = fopen(offset_file_name, "r");
+ if (!f)
+ return -errno;
+
+ rc = fread(offset, sizeof(*offset), 1, f);
+ fclose(f);
+
+ return rc == 1 ? 0 : -EINVAL;
+}
+
+static int write_offset(struct timeval offset)
+{
+ FILE *f;
+ int rc;
+ f = fopen(offset_file_name, "w");
+ if (!f)
+ return -errno;
+
+ rc = fwrite(&offset, sizeof(offset), 1, f);
+ fclose(f);
+
+ return rc == 1 ? 0 : -EINVAL;
+}
+
+
/*
* Read the adjustment parameters out of the /etc/adjtime file.
*
@@ -1290,6 +1320,8 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
bool no_auth;
/* The time at which we read the Hardware Clock */
struct timeval read_time;
+ /* The offset between system time and hardware time */
+ struct timeval offset = {0};
/*
* The Hardware Clock gives us a valid time, or at
* least something close enough to fool mktime().
@@ -1320,6 +1352,11 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
adjtime.dirty = FALSE;
}
+ if ((hctosys || show) && offset_file_name)
+ {
+ read_offset(&offset);
+ }
+
universal = hw_clock_is_utc(utc, local_opt, adjtime);
if ((set || systohc || adjust) &&
@@ -1328,7 +1365,8 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
adjtime.dirty = TRUE;
}
- if (show || adjust || hctosys || (!noadjfile && !systz && !predict)) {
+ if (show || adjust || hctosys || (!noadjfile && !systz && !predict) ||
+ offset_file_name) {
/* data from HW-clock are required */
rc = synchronize_to_clock_tick();
@@ -1358,8 +1396,20 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
}
if (show) {
- display_time(hclock_valid, hclocktime,
+ display_time(hclock_valid, hclocktime + offset.tv_sec,
time_diff(read_time, startup_time));
+ } else if (set && offset_file_name) {
+ if (!hclock_valid) {
+ printf(_("Hardware clock invalid, not writing offset.\n"));
+ } else {
+ offset.tv_sec = set_time - hclocktime;
+ rc = write_offset(offset);
+ if (rc) {
+ printf(_("Unable to write offset: %s."), strerror(-rc));
+ return rc;
+ }
+ }
+
} else if (set) {
set_hardware_clock_exact(set_time, startup_time,
universal, testing);
@@ -1371,6 +1421,18 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
} else if (adjust) {
do_adjustment(&adjtime, hclock_valid,
hclocktime, read_time, universal, testing);
+ } else if (systohc && offset_file_name) {
+ if (!hclock_valid) {
+ printf(_("Hardware clock invalid, not writing offset.\n"));
+ } else {
+ gettimeofday(&offset, NULL);
+ offset.tv_sec -= hclocktime;
+ rc = write_offset(offset);
+ if (rc) {
+ printf(_("Unable to write offset: %s."), strerror(-rc));
+ return rc;
+ }
+ }
} else if (systohc) {
struct timeval nowtime, reftime;
/*
@@ -1390,6 +1452,17 @@ manipulate_clock(const bool show, const bool adjust, const bool noadjfile,
reftime.tv_sec,
hclock_valid, hclocktime, (double)
read_time.tv_usec / 1E6);
+ } else if (hctosys && offset_file_name) {
+ if (!hclock_valid) {
+ printf(_("Hardware clock invalid, not setting time.\n"));
+ } else {
+ offset.tv_sec += hclocktime;
+ rc = settimeofday(&offset, NULL);
+ if (rc) {
+ printf(_("Unable to set system clock.\n"));
+ return rc;
+ }
+ }
} else if (hctosys) {
rc = set_system_clock(hclock_valid, hclocktime, testing);
if (rc) {
@@ -1547,6 +1620,7 @@ static void out_version(void)
printf(UTIL_LINUX_VERSION);
}
+#define DEFAULT_OFFSET_FILE "/etc/time_offset"
/*
* usage - Output (error and) usage information
*
@@ -1577,6 +1651,10 @@ static void usage(const char *fmt, ...)
" --adjust adjust the RTC to account for systematic drift since\n"
" the clock was last set or adjusted\n"), usageto);
fputs(_(" -c, --compare periodically compare the system clock with the CMOS clock\n"), usageto);
+ fprintf(usageto,
+ _(" --offset [file] instead of setting the clock, write an offset to file.\n"
+ " when reading the time, add this offset to the hardware time.\n"
+ " (default: %s)\n"), DEFAULT_OFFSET_FILE);
#ifdef __linux__
fputs(_(" --getepoch print out the kernel's hardware clock epoch value\n"
" --setepoch set the kernel's hardware clock epoch value to the \n"
@@ -1653,6 +1731,7 @@ int main(int argc, char **argv)
/* Long only options. */
enum {
OPT_ADJFILE = CHAR_MAX + 1,
+ OPT_OFFSET,
OPT_BADYEAR,
OPT_DATE,
OPT_DIRECTISA,
@@ -1698,6 +1777,7 @@ int main(int argc, char **argv)
{"test", 0, 0, OPT_TEST},
{"date", 1, 0, OPT_DATE},
{"epoch", 1, 0, OPT_EPOCH},
+ {"offset", 2, 0, OPT_OFFSET},
#ifdef __linux__
{"rtc", 1, 0, 'f'},
#endif
@@ -1837,6 +1917,10 @@ int main(int argc, char **argv)
case OPT_PREDICT_HC:
predict = TRUE; /* --predict-hc */
break;
+ case OPT_OFFSET:
+ offset_file_name = /* --offset */
+ optarg ? optarg : DEFAULT_OFFSET_FILE;
+ break;
#ifdef __linux__
case 'f':
rtc_dev_name = optarg; /* --rtc */
--
2.1.0
--
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