getloadavg() interface

lib/posix/Makefile

@@ -100,6 +100,7 @@ libc_OBJECTS	= \
 	_readlink.o \
 	_symlink.o \
 	usleep.o \
+	getloadavg.o
 
 include ../Makefile.inc
 

lib/posix/getloadavg.c

@@ -0,0 +1,56 @@
+
+#include <sys/types.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <lib.h>
+
+/* Retrieve system load average information. */
+int getloadavg(double *loadavg, int nelem)
+{
+  struct loadinfo loadinfo;
+  int h, p, unfilled_ticks;
+#define PERIODS 3
+  int minutes[3] = { 1, 5, 15 };
+  if(nelem < 1) {
+	errno = ENOSPC;
+	return -1;
+  }
+
+  if(getsysinfo(PM_PROC_NR, SI_LOADINFO, &loadinfo) < 0)
+	return -1;
+  if(nelem > PERIODS)
+	nelem = PERIODS;
+
+  /* How many ticks are missing from the newest-filled slot? */
+#define TICKSPERSLOT (_LOAD_UNIT_SECS * HZ)
+  unfilled_ticks = TICKSPERSLOT - (loadinfo.last_clock % TICKSPERSLOT);
+
+  for(p = 0; p < nelem; p++) {
+    int h, offset, slots;
+    double l = 0.0;
+    int latest = loadinfo.proc_last_slot;
+    slots = minutes[p] * 60 / _LOAD_UNIT_SECS;
+
+    /* Add up the total number of process ticks for this number
+     * of minutes (minutes[p]). Start with the newest slot, which
+     * is latest, and count back for the number of slots that 
+     * correspond to the right number of minutes. Take wraparound
+     * into account by calculating the index modulo _LOAD_HISTORY,
+     * which is the number of slots of history kept.
+     */
+    for(h = 0; h < slots; h++) {
+       int slot;
+       slot = (latest - h + _LOAD_HISTORY) % _LOAD_HISTORY;
+       l += (double) loadinfo.proc_load_history[slot];
+    }
+
+    /* The load average over this number of minutes is the number of
+     * process-ticks divided by the number of ticks, not counting the
+     * number of ticks the last slot hasn't been around yet.
+     */
+    loadavg[p] = l / (slots * TICKSPERSLOT - unfilled_ticks);
+  }
+
+  return nelem;
+}
+