add support for $ibm_thinklight

Some IBM/Lenovo models come with a light on the top edge of the
display to illuminate the keyboard. This either reports 'on', 'off'
or 'unknown'.

doc/variables.xml

@@ -1676,6 +1676,16 @@
         Sensor 0 is on the CPU, 3 is on the GPU. 
         <para /></listitem>
     </varlistentry>
+    <varlistentry>
+        <term>
+            <command>
+                <option>ibm_thinklight</option>
+            </command>
+        </term>
+        <listitem>If running the IBM ACPI, displays the status of your
+            ThinkLight™. Value is either 'on', 'off' or 'unknown'.
+            <para /></listitem>
+    </varlistentry>
     <varlistentry>
         <term>
             <command>

src/core.cc

@@ -509,6 +509,8 @@ struct text_object *construct_text_object(char *s, const char *arg,
 		obj->callbacks.print = &get_ibm_acpi_volume;
 	END OBJ(ibm_brightness, 0)
 		obj->callbacks.print = &get_ibm_acpi_brightness;
+	END OBJ(ibm_thinklight, 0)
+		obj->callbacks.print = &get_ibm_acpi_thinklight;
 #endif
 	/* information from sony_laptop kernel module
 	 * /sys/devices/platform/sony-laptop */

src/ibm.cc

@@ -261,6 +261,50 @@ void get_ibm_acpi_brightness(struct text_object *obj, char *p, int p_max_size)
 	snprintf(p, p_max_size, "%d", brightness);
 }
 
+/* get ThinkLight status on IBM/Lenovo laptops running the ibm acpi.
+ * /proc/acpi/ibm/light looks like this (2 lines):
+status:         off
+commands:       on, off
+ * http://ibm-acpi.sourceforge.net/README reports that it's also possible to
+ * get "unknown" for a few models that do not make the status available.
+ * Lluis Esquerda (eskerda@gmail.com) */
+
+void get_ibm_acpi_thinklight(struct text_object *obj, char *p, int p_max_size)
+{
+	FILE *fp;
+	char thinklight[8];
+	char filename[128];
+
+	(void)obj;
+
+	if (!p || p_max_size <= 0) {
+		return;
+	}
+
+	snprintf(filename, 127, "%s/light", IBM_ACPI_DIR);
+
+	fp = fopen(filename, "r");
+	if (fp != NULL) {
+		while (!feof(fp)) {
+			char line[256];
+
+			if (fgets(line, 255, fp) == NULL) {
+				break;
+			}
+			if (sscanf(line, "status: %s", thinklight)) {
+				break;
+			}
+		}
+	} else {
+		CRIT_ERR(NULL, NULL, "can't open '%s': %s\nYou are not using the IBM "
+			"ACPI. Remove ibm* from your " PACKAGE_NAME" config file.",
+			filename, strerror(errno));
+	}
+
+	fclose(fp);
+	snprintf(p, p_max_size, "%s", thinklight);
+}
+
 void parse_ibm_temps_arg(struct text_object *obj, const char *arg)
 {
 	if (!isdigit(arg[0]) || strlen(arg) > 1 || atoi(&arg[0]) >= 8) {

src/ibm.h

@@ -30,6 +30,7 @@ void get_ibm_acpi_fan(struct text_object *, char *, int);
 int get_ibm_acpi_temps(void);
 void get_ibm_acpi_volume(struct text_object *, char *, int);
 void get_ibm_acpi_brightness(struct text_object *, char *, int);
+void get_ibm_acpi_thinklight(struct text_object *, char *, int);
 
 void parse_ibm_temps_arg(struct text_object *, const char *);
 void print_ibm_temps(struct text_object *, char *, int);