hwclock: add --rtc=<path> option and support for /dev/rtc0

The patch to allow "hwclock --rtc /dev/rtc1" and so on,
since "/dev/rtc" may not be there and "/dev/rtc0" may not be
the right answer either.

The "--rtc" is compatible with next Bryan Henderson's hwclock
versions.

Signed-off-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Karel Zak <kzak@redhat.com>

4 files changed, 73 insertions, 25 deletions

diff --git a/hwclock/clock.h b/hwclock/clock.h
index 91d3df801..f1d00e493 100644
--- a/hwclock/clock.h
+++ b/hwclock/clock.h
@@ -33,3 +33,4 @@ extern void set_cmos_access(int Jensen, int funky_toy);
 /* rtc.c */
 extern int get_epoch_rtc(unsigned long *epoch, int silent);
 extern int set_epoch_rtc(unsigned long epoch);
+extern char *rtc_dev_name;
diff --git a/hwclock/hwclock.8 b/hwclock/hwclock.8
index e3fcb4147..37d80e79b 100644
--- a/hwclock/hwclock.8
+++ b/hwclock/hwclock.8
@@ -22,6 +22,7 @@ other options:
 .PP
 .B "[\-u|\-\-utc]  \-\-localtime  \-\-noadjfile \-\-directisa"
 .B "\-\-test [\-D|\-\-debug]"
+.B "\-\-rtc=filename"
 .PP
 and arcane options for DEC Alpha:
 .PP
@@ -182,6 +183,15 @@ or
 must be specified when using this option.
 
 .TP
+.B \-\-rtc=filename
+overrides the default /dev file name, which is
+.IR /dev/rtc
+on many platforms but may be
+.IR /dev/rtc0 ,
+.IR /dev/rtc1 ,
+and so on.
+
+.TP
 .B \-\-directisa
 is meaningful only on an ISA machine or an Alpha (which implements enough
 of ISA to be, roughly speaking, an ISA machine for 
@@ -314,6 +324,12 @@ capitalized form, was coined for use by
 because all of the other names are inappropriate to the point of being
 misleading.
 .PP
+So for example, some non-ISA systems have a few real time clocks with
+only one of them having its own power domain.
+A very low power external I2C or SPI clock chip might be used with a
+backup battery as the hardware clock to initialize a more functional
+integrated real-time clock which is used for most other purposes.
+.PP
 .B The System Time: 
 This is the time kept by a clock inside the Linux kernel and driven by
 a timer interrupt.  (On an ISA machine, the timer interrupt is part of
@@ -381,6 +397,13 @@ a relatively recent addition to Linux.  Older systems don't have it.
 Also, though there are versions of the rtc driver that work on DEC
 Alphas, there appear to be plenty of Alphas on which the rtc driver
 does not work (a common symptom is hwclock hanging).
+Moreover, recent Linux systems have more generic support for RTCs,
+even systems that have more than one, so you might need to override
+the default by specifying
+.I /dev/rtc0
+or
+.I /dev/rtc1
+instead.
 .PP
 On older systems, the method of accessing the Hardware Clock depends on
 the system hardware. 
@@ -411,7 +434,8 @@ file /dev/tty1.
 .PP
 .B hwclock 
 tries to use /dev/rtc.  If it is compiled for a kernel that doesn't have
-that function or it is unable to open /dev/rtc, 
+that function or it is unable to open /dev/rtc
+(or the alternative special file you've defined on the command line)
 .B hwclock 
 will fall back to another method, if available.  On an ISA or Alpha
 machine, you can force
@@ -569,8 +593,8 @@ maintainer; an option may be appropriate.
 
 Note that this section is only relevant when you are using the "direct
 ISA" method of accessing the Hardware Clock.
-
-
+ACPI provides a standard way to access century values, when they
+are supported by the hardware.
 
 .SH "ENVIRONMENT VARIABLES"
 .I TZ
@@ -581,6 +605,7 @@ ISA" method of accessing the Hardware Clock.
 .RI ( /usr/lib/zoneinfo
 on old systems)
 .I /dev/rtc
+.I /dev/rtc0
 .I /dev/port
 .I /dev/tty1
 .I /proc/cpuinfo
diff --git a/hwclock/hwclock.c b/hwclock/hwclock.c
index ec8681527..9731dadfb 100644
--- a/hwclock/hwclock.c
+++ b/hwclock/hwclock.c
@@ -1210,6 +1210,7 @@ usage( const char *fmt, ... ) {
     "\nOptions: \n"
     "  --utc         the hardware clock is kept in coordinated universal time\n"
     "  --localtime   the hardware clock is kept in local time\n"
+    "  --rtc=path    special /dev/... file to use instead of default\n"
     "  --directisa   access the ISA bus directly instead of %s\n"
     "  --badyear     ignore rtc's year because the bios is broken\n"
     "  --date        specifies the time to which to set the hardware clock\n"
@@ -1265,6 +1266,7 @@ static const struct option longopts[] = {
 	{ "test", 0, 0, 135 },
 	{ "date", 1, 0, 136 },
 	{ "epoch", 1, 0, 137 },
+	{ "rtc", 1, 0, 'f' },
 	{ NULL, 0, 0, 0 }
 };
 
@@ -1314,7 +1316,7 @@ main(int argc, char **argv) {
 	ARCconsole = Jensen = SRM = funky_toy = directisa = badyear = FALSE;
 	date_opt = NULL;
 
-	while ((c = getopt_long (argc, argv, "?hvVDarsuwAJSF", longopts, NULL))
+	while ((c = getopt_long (argc, argv, "?hvVDarsuwAJSFf:", longopts, NULL))
 	       != -1) {
 		switch (c) {
 		case 'D':
@@ -1379,6 +1381,9 @@ main(int argc, char **argv) {
 		case 137:
 			epoch_option = atoi(optarg);	/* --epoch */
 			break;
+		case 'f':
+			rtc_dev_name = optarg;		/* --rtc */
+			break;
 		case 'v':				/* --version */
 		case 'V':
 			out_version();
diff --git a/hwclock/rtc.c b/hwclock/rtc.c
index 3876da93a..33be42bbe 100644
--- a/hwclock/rtc.c
+++ b/hwclock/rtc.c
@@ -82,30 +82,47 @@ struct linux_rtc_time {
 #define RTC_EPOCH_SET	_IOW('p', 0x0e, unsigned long)	 /* Set epoch */
 #endif
 
+/* /dev/rtc is conventionally chardev 10/135
+ * ia64 uses /dev/efirtc, chardev 10/136
+ * devfs (obsolete) used /dev/misc/... for miscdev
+ * new RTC framework + udev uses dynamic major and /dev/rtc0.../dev/rtcN
+ * ... so we need an overridable default
+ */
 
-/* ia64 uses /dev/efirtc (char 10,136) */
-/* devfs uses /dev/misc/rtc */
-#ifdef __ia64__
-#define RTC_DEVN	"efirtc"
-#else
-#define RTC_DEVN	"rtc"
-#endif
-
-static char *rtc_dev_name;
+/* default or user defined dev (by hwclock --rtc=<path>) */
+char *rtc_dev_name;
 
 static int
 open_rtc(void) {
-	int rtc_fd;
-
-	rtc_dev_name = "/dev/" RTC_DEVN;
-	rtc_fd = open(rtc_dev_name, O_RDONLY);
-	if (rtc_fd < 0 && errno == ENOENT) {
-		rtc_dev_name = "/dev/misc/" RTC_DEVN;
-		rtc_fd = open(rtc_dev_name, O_RDONLY);
-		if (rtc_fd < 0 && errno == ENOENT)
-			rtc_dev_name = "/dev/" RTC_DEVN;
-	}
-	return rtc_fd;
+	char *fls[] = {
+#ifdef __ia64__
+		"/dev/efirtc",
+		"/dev/misc/efirtc",
+#endif
+		"/dev/rtc",
+		"/dev/rtc0",
+		"/dev/misc/rtc",
+		NULL
+	};
+	char **p = fls;
+	char *fname = rtc_dev_name ? : *p;
+
+	do {
+		int fd = open(fname, O_RDONLY);
+
+		if (fd < 0 && errno == ENOENT) {
+			if (fname == rtc_dev_name)
+				break;
+			fname = *++p;
+		} else {
+			rtc_dev_name = *p;
+			return fd;
+		}
+	} while(fname);
+
+	if (!rtc_dev_name)
+		rtc_dev_name = *fls;
+	return -1;
 }
 
 static int
@@ -346,7 +363,7 @@ get_permissions_rtc(void) {
 }
 
 static struct clock_ops rtc = {
-	"/dev/" RTC_DEVN " interface to clock",
+	"/dev interface to clock",
 	get_permissions_rtc,
 	read_hardware_clock_rtc,
 	set_hardware_clock_rtc,