aio / timers: add qemu-timer.c utility functions

Add utility functions to qemu-timer.c for nanosecond timing.

Add qemu_clock_deadline_ns to calculate deadlines to
nanosecond accuracy.

Add utility function qemu_soonest_timeout to calculate soonest deadline.

Add qemu_timeout_ns_to_ms to convert a timeout in nanoseconds back to
milliseconds for when ppoll is not used.

Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

include/qemu/timer.h

@@ -40,6 +40,29 @@ int64_t qemu_get_clock_ns(QEMUClock *clock);
 int64_t qemu_clock_has_timers(QEMUClock *clock);
 int64_t qemu_clock_expired(QEMUClock *clock);
 int64_t qemu_clock_deadline(QEMUClock *clock);
+
+/**
+ * qemu_clock_deadline_ns:
+ * @clock: the clock to operate on
+ *
+ * Calculate the timeout of the earliest expiring timer
+ * in nanoseconds, or -1 if no timer is set to expire.
+ *
+ * Returns: time until expiry in nanoseconds or -1
+ */
+int64_t qemu_clock_deadline_ns(QEMUClock *clock);
+
+/**
+ * qemu_timeout_ns_to_ms:
+ * @ns: nanosecond timeout value
+ *
+ * Convert a nanosecond timeout value (or -1) to
+ * a millisecond value (or -1), always rounding up.
+ *
+ * Returns: millisecond timeout value
+ */
+int qemu_timeout_ns_to_ms(int64_t ns);
+
 void qemu_clock_enable(QEMUClock *clock, bool enabled);
 void qemu_clock_warp(QEMUClock *clock);
 
@@ -67,6 +90,25 @@ int64_t cpu_get_ticks(void);
 void cpu_enable_ticks(void);
 void cpu_disable_ticks(void);
 
+/**
+ * qemu_soonest_timeout:
+ * @timeout1: first timeout in nanoseconds (or -1 for infinite)
+ * @timeout2: second timeout in nanoseconds (or -1 for infinite)
+ *
+ * Calculates the soonest of two timeout values. -1 means infinite, which
+ * is later than any other value.
+ *
+ * Returns: soonest timeout value in nanoseconds (or -1 for infinite)
+ */
+static inline int64_t qemu_soonest_timeout(int64_t timeout1, int64_t timeout2)
+{
+    /* we can abuse the fact that -1 (which means infinite) is a maximal
+     * value when cast to unsigned. As this is disgusting, it's kept in
+     * one inline function.
+     */
+    return ((uint64_t) timeout1 < (uint64_t) timeout2) ? timeout1 : timeout2;
+}
+
 static inline QEMUTimer *qemu_new_timer_ns(QEMUClock *clock, QEMUTimerCB *cb,
                                            void *opaque)
 {

qemu-timer.c

@@ -273,6 +273,56 @@ int64_t qemu_clock_deadline(QEMUClock *clock)
     return delta;
 }
 
+/*
+ * As above, but return -1 for no deadline, and do not cap to 2^32
+ * as we know the result is always positive.
+ */
+
+int64_t qemu_clock_deadline_ns(QEMUClock *clock)
+{
+    int64_t delta;
+
+    if (!clock->enabled || !clock->active_timers) {
+        return -1;
+    }
+
+    delta = clock->active_timers->expire_time - qemu_get_clock_ns(clock);
+
+    if (delta <= 0) {
+        return 0;
+    }
+
+    return delta;
+}
+
+/* Transition function to convert a nanosecond timeout to ms
+ * This is used where a system does not support ppoll
+ */
+int qemu_timeout_ns_to_ms(int64_t ns)
+{
+    int64_t ms;
+    if (ns < 0) {
+        return -1;
+    }
+
+    if (!ns) {
+        return 0;
+    }
+
+    /* Always round up, because it's better to wait too long than to wait too
+     * little and effectively busy-wait
+     */
+    ms = (ns + SCALE_MS - 1) / SCALE_MS;
+
+    /* To avoid overflow problems, limit this to 2^31, i.e. approx 25 days */
+    if (ms > (int64_t) INT32_MAX) {
+        ms = INT32_MAX;
+    }
+
+    return (int) ms;
+}
+
+
 QEMUTimer *qemu_new_timer(QEMUClock *clock, int scale,
                           QEMUTimerCB *cb, void *opaque)
 {