sensor: Expose max id of sensor device through hw.sensors.dev_idmax

There could be so many sensor devices that MAXSENSORDEVICES is far
from enough, e.g. coretemp.

sys/kern/kern_sensors.c

@@ -36,7 +36,8 @@
 
 #include <sys/mplock2.h>
 
-static TAILQ_HEAD(, ksensordev) sensordev_list =
+static int		sensordev_idmax;
+static TAILQ_HEAD(sensordev_list, ksensordev) sensordev_list =
     TAILQ_HEAD_INITIALIZER(sensordev_list);
 
 static struct ksensordev *sensordev_get(int);
@@ -94,6 +95,9 @@ sensordev_install(struct ksensordev *sensdev)
 		TAILQ_INSERT_AFTER(&sensordev_list, after, sensdev, list);
 	}
 
+	/* Save max sensor device id */
+	sensordev_idmax = TAILQ_LAST(&sensordev_list, sensordev_list)->num + 1;
+
 	/* Install sysctl node for this sensor device */
 	sensordev_sysctl_install(sensdev);
 
@@ -145,10 +149,19 @@ sensor_attach(struct ksensordev *sensdev, struct ksensor *sens)
 void
 sensordev_deinstall(struct ksensordev *sensdev)
 {
+	struct ksensordev *last;
+
 	SYSCTL_XLOCK();
 
 	TAILQ_REMOVE(&sensordev_list, sensdev, list);
 
+	/* Adjust max sensor device id */
+	last = TAILQ_LAST(&sensordev_list, sensordev_list);
+	if (last != NULL)
+		sensordev_idmax = last->num + 1;
+	else
+		sensordev_idmax = 0;
+
 	/*
 	 * Deinstall sensor device's sysctl node; this also
 	 * removes all attached sensors' sysctl nodes.
@@ -322,6 +335,9 @@ SYSCTL_NODE(_hw, OID_AUTO, sensors, CTLFLAG_RD, NULL,
 SYSCTL_NODE(_hw, HW_SENSORS, _sensors, CTLFLAG_RD, sysctl_sensors_handler,
     "Hardware Sensors XP MIB interface");
 
+SYSCTL_INT(_hw_sensors, OID_AUTO, dev_idmax, CTLFLAG_RD,
+    &sensordev_idmax, 0, "Max sensor device id");
+
 static void
 sensordev_sysctl_install(struct ksensordev *sensdev)
 {

usr.bin/systat/sensors.c

@@ -67,8 +67,15 @@ void
 fetchsensors(void)
 {
 	enum sensor_type type;
-	size_t		 slen, sdlen;
-	int		 mib[5], dev, numt;
+	size_t		 slen, sdlen, idmax_len;
+	int		 mib[5], dev, numt, idmax;
+	int		 maxsensordevices;
+
+	maxsensordevices = MAXSENSORDEVICES;
+	idmax_len = sizeof(idmax);
+	if (sysctlbyname("hw.sensors.dev_idmax", &idmax, &idmax_len,
+	    NULL, 0) == 0)
+		maxsensordevices = idmax;
 
 	mib[0] = CTL_HW;
 	mib[1] = HW_SENSORS;
@@ -81,7 +88,7 @@ fetchsensors(void)
 	wmove(wnd, row, 0);
 	wclrtobot(wnd);
 
-	for (dev = 0; dev < MAXSENSORDEVICES; dev++) {
+	for (dev = 0; dev < maxsensordevices; dev++) {
 		mib[2] = dev;
 		if (sysctl(mib, 3, &sensordev, &sdlen, NULL, 0) == -1) {
 			if (errno != ENOENT)