+#include <signal.h>
+#include <errno.h>
+#include "user_util.h"
+#include "kern_util.h"
+#include "user.h"
+#include "process.h"
+#include "kern_constants.h"
+#include "os.h"
+
+/* XXX This really needs to be declared and initialized in a kernel file since
+ * it's in <linux/time.h>
+ */
+extern struct timespec wall_to_monotonic;
+
+static void set_interval(int timer_type)
+{
+ int usec = 1000000/hz();
+ struct itimerval interval = ((struct itimerval) { { 0, usec },
+ { 0, usec } });
+
+ if(setitimer(timer_type, &interval, NULL) == -1)
+ panic("setitimer failed - errno = %d\n", errno);
+}
+
+void enable_timer(void)
+{
+ set_interval(ITIMER_VIRTUAL);
+}
+
+void disable_timer(void)
+{
+ struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
+ if((setitimer(ITIMER_VIRTUAL, &disable, NULL) < 0) ||
+ (setitimer(ITIMER_REAL, &disable, NULL) < 0))
+ printk("disnable_timer - setitimer failed, errno = %d\n",
+ errno);
+ /* If there are signals already queued, after unblocking ignore them */
+ set_handler(SIGALRM, SIG_IGN, 0, -1);
+ set_handler(SIGVTALRM, SIG_IGN, 0, -1);
+}
+
+void switch_timers(int to_real)
+{
+ struct itimerval disable = ((struct itimerval) { { 0, 0 }, { 0, 0 }});
+ struct itimerval enable = ((struct itimerval) { { 0, 1000000/hz() },
+ { 0, 1000000/hz() }});
+ int old, new;
+
+ if(to_real){
+ old = ITIMER_VIRTUAL;
+ new = ITIMER_REAL;
+ }
+ else {
+ old = ITIMER_REAL;
+ new = ITIMER_VIRTUAL;
+ }