slstatus: add cpu_iowait

This commit introduces the cpu_iowait item, this is the percentage
of cpu time spent waiting on disks. High numbers typically indicate
that your system is not responsive due to disk IO.
This commit also avoid sleeping inside the cpu_perc and cpu_iowait
functions: waiting in either one implies lost info for the other.

Signed-off-by: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>

config.def.h

@@ -16,6 +16,7 @@ static const char unknown_str[] = "n/a";
  * battery_power        battery power usage             battery name
  * battery_state        battery charging state          battery name
  * cpu_perc             cpu usage in percent            NULL
+ * cpu_iowait           cpu iowait in percent           NULL
  * cpu_freq             cpu frequency in MHz            NULL
  * datetime             date and time                   format string
  * disk_free            free disk space in GB           mountpoint path

slstatus.c

@@ -40,6 +40,7 @@ static const char *battery_power(const char *bat);
 static const char *battery_state(const char *bat);
 static const char *cpu_freq(void);
 static const char *cpu_perc(void);
+static const char *cpu_iowait(void);
 static const char *datetime(const char *fmt);
 static const char *disk_free(const char *mnt);
 static const char *disk_perc(const char *mnt);
@@ -177,26 +178,47 @@ cpu_freq(void)
 static const char *
 cpu_perc(void)
 {
-	struct timespec delay;
 	int perc;
-	long double a[4], b[4];
+	static long double a[7];
+	static int valid;
+	long double b[7];
 
-	if (pscanf("/proc/stat", "%*s %Lf %Lf %Lf %Lf", &a[0], &a[1], &a[2],
-	           &a[3]) != 4) {
+	memcpy(b, a, sizeof(b));
+	if (pscanf("/proc/stat", "%*s %Lf %Lf %Lf %Lf %Lf %Lf %Lf", &a[0], &a[1], &a[2],
+	           &a[3], &a[4], &a[5], &a[6]) != 7) {
 		return unknown_str;
 	}
+	if (!valid) {
+		valid = 1;
+		return unknown_str;
+	}
+
+	perc = 100 * ((b[0]+b[1]+b[2]+b[5]+b[6]) - (a[0]+a[1]+a[2]+a[5]+a[6])) /
+	       ((b[0]+b[1]+b[2]+b[3]+b[4]+b[5]+b[6]) - (a[0]+a[1]+a[2]+a[3]+a[4]+a[5]+a[6]));
 
-	delay.tv_sec = (interval / 2) / 1000;
-	delay.tv_nsec = ((interval / 2) % 1000) * 1000000;
-	nanosleep(&delay, NULL);
+	return bprintf("%d", perc);
+}
 
-	if (pscanf("/proc/stat", "%*s %Lf %Lf %Lf %Lf", &b[0], &b[1], &b[2],
-	           &b[3]) != 4) {
+static const char *
+cpu_iowait(void)
+{
+	int perc;
+	static int valid;
+	static long double a[7];
+	long double b[7];
+
+	memcpy(b, a, sizeof(b));
+	if (pscanf("/proc/stat", "%*s %Lf %Lf %Lf %Lf %Lf %Lf %Lf", &a[0], &a[1], &a[2],
+	           &a[3], &a[4], &a[5], &a[6]) != 7) {
+		return unknown_str;
+	}
+	if (!valid) {
+		valid = 1;
 		return unknown_str;
 	}
 
-	perc = 100 * ((b[0]+b[1]+b[2]) - (a[0]+a[1]+a[2])) /
-	       ((b[0]+b[1]+b[2]+b[3]) - (a[0]+a[1]+a[2]+a[3]));
+	perc = 100 * ((b[4]) - (a[4])) /
+	       ((b[0]+b[1]+b[2]+b[3]+b[4]+b[5]+b[6]) - (a[0]+a[1]+a[2]+a[3]+a[4]+a[5]+a[6]));
 
 	return bprintf("%d", perc);
 }