qemu-coroutine-sleep: introduce qemu_co_sleep_wake

Introduce a function to gracefully wake a coroutine sleeping in
qemu_co_sleep_ns().

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20191009084158.15614-2-vsementsov@virtuozzo.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

include/qemu/coroutine.h

@@ -273,10 +273,29 @@ void qemu_co_rwlock_wrlock(CoRwlock *lock);
  */
 void qemu_co_rwlock_unlock(CoRwlock *lock);
 
+typedef struct QemuCoSleepState QemuCoSleepState;
+
+/**
+ * Yield the coroutine for a given duration. During this yield, @sleep_state
+ * (if not NULL) is set to an opaque pointer, which may be used for
+ * qemu_co_sleep_wake(). Be careful, the pointer is set back to zero when the
+ * timer fires. Don't save the obtained value to other variables and don't call
+ * qemu_co_sleep_wake from another aio context.
+ */
+void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
+                                            QemuCoSleepState **sleep_state);
+static inline void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
+{
+    qemu_co_sleep_ns_wakeable(type, ns, NULL);
+}
+
 /**
- * Yield the coroutine for a given duration
+ * Wake a coroutine if it is sleeping in qemu_co_sleep_ns. The timer will be
+ * deleted. @sleep_state must be the variable whose address was given to
+ * qemu_co_sleep_ns() and should be checked to be non-NULL before calling
+ * qemu_co_sleep_wake().
  */
-void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns);
+void qemu_co_sleep_wake(QemuCoSleepState *sleep_state);
 
 /**
  * Yield until a file descriptor becomes readable

util/qemu-coroutine-sleep.c

@@ -17,31 +17,56 @@
 #include "qemu/timer.h"
 #include "block/aio.h"
 
-static void co_sleep_cb(void *opaque)
-{
-    Coroutine *co = opaque;
+static const char *qemu_co_sleep_ns__scheduled = "qemu_co_sleep_ns";
+
+struct QemuCoSleepState {
+    Coroutine *co;
+    QEMUTimer *ts;
+    QemuCoSleepState **user_state_pointer;
+};
 
+void qemu_co_sleep_wake(QemuCoSleepState *sleep_state)
+{
     /* Write of schedule protected by barrier write in aio_co_schedule */
-    atomic_set(&co->scheduled, NULL);
-    aio_co_wake(co);
+    const char *scheduled = atomic_cmpxchg(&sleep_state->co->scheduled,
+                                           qemu_co_sleep_ns__scheduled, NULL);
+
+    assert(scheduled == qemu_co_sleep_ns__scheduled);
+    if (sleep_state->user_state_pointer) {
+        *sleep_state->user_state_pointer = NULL;
+    }
+    timer_del(sleep_state->ts);
+    aio_co_wake(sleep_state->co);
 }
 
-void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
+static void co_sleep_cb(void *opaque)
+{
+    qemu_co_sleep_wake(opaque);
+}
+
+void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
+                                            QemuCoSleepState **sleep_state)
 {
     AioContext *ctx = qemu_get_current_aio_context();
-    QEMUTimer *ts;
-    Coroutine *co = qemu_coroutine_self();
+    QemuCoSleepState state = {
+        .co = qemu_coroutine_self(),
+        .ts = aio_timer_new(ctx, type, SCALE_NS, co_sleep_cb, &state),
+        .user_state_pointer = sleep_state,
+    };
 
-    const char *scheduled = atomic_cmpxchg(&co->scheduled, NULL, __func__);
+    const char *scheduled = atomic_cmpxchg(&state.co->scheduled, NULL,
+                                           qemu_co_sleep_ns__scheduled);
     if (scheduled) {
         fprintf(stderr,
                 "%s: Co-routine was already scheduled in '%s'\n",
                 __func__, scheduled);
         abort();
     }
-    ts = aio_timer_new(ctx, type, SCALE_NS, co_sleep_cb, co);
-    timer_mod(ts, qemu_clock_get_ns(type) + ns);
+
+    if (sleep_state) {
+        *sleep_state = &state;
+    }
+    timer_mod(state.ts, qemu_clock_get_ns(type) + ns);
     qemu_coroutine_yield();
-    timer_del(ts);
-    timer_free(ts);
+    timer_free(state.ts);
 }