coroutine-sleep: replace QemuCoSleepState pointer with struct in the API

Right now, users of qemu_co_sleep_ns_wakeable are simply passing
a pointer to QemuCoSleepState by reference to the function.  But
QemuCoSleepState really is just a Coroutine*; making the
content of the struct public is just as efficient and lets us
skip the user_state_pointer indirection.

Since the usage is changed, take the occasion to rename the
struct to QemuCoSleep.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210517100548.28806-6-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/block-copy.c

@@ -50,7 +50,7 @@ typedef struct BlockCopyCallState {
     /* State */
     int ret;
     bool finished;
-    QemuCoSleepState *sleep_state;
+    QemuCoSleep sleep;
     bool cancelled;
 
     /* OUT parameters */
@@ -625,8 +625,8 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
                 if (ns > 0) {
                     block_copy_task_end(task, -EAGAIN);
                     g_free(task);
-                    qemu_co_sleep_ns_wakeable(QEMU_CLOCK_REALTIME, ns,
-                                              &call_state->sleep_state);
+                    qemu_co_sleep_ns_wakeable(&call_state->sleep,
+                                              QEMU_CLOCK_REALTIME, ns);
                     continue;
                 }
             }
@@ -674,7 +674,7 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
 
 void block_copy_kick(BlockCopyCallState *call_state)
 {
-    qemu_co_sleep_wake(call_state->sleep_state);
+    qemu_co_sleep_wake(&call_state->sleep);
 }
 
 /*

block/nbd.c

@@ -116,7 +116,7 @@ typedef struct BDRVNBDState {
     CoQueue free_sema;
     Coroutine *connection_co;
     Coroutine *teardown_co;
-    QemuCoSleepState *connection_co_sleep_ns_state;
+    QemuCoSleep reconnect_sleep;
     bool drained;
     bool wait_drained_end;
     int in_flight;
@@ -289,7 +289,7 @@ static void coroutine_fn nbd_client_co_drain_begin(BlockDriverState *bs)
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     s->drained = true;
-    qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
+    qemu_co_sleep_wake(&s->reconnect_sleep);
 
     nbd_co_establish_connection_cancel(bs, false);
 
@@ -328,7 +328,7 @@ static void nbd_teardown_connection(BlockDriverState *bs)
 
     s->state = NBD_CLIENT_QUIT;
     if (s->connection_co) {
-        qemu_co_sleep_wake(s->connection_co_sleep_ns_state);
+        qemu_co_sleep_wake(&s->reconnect_sleep);
         nbd_co_establish_connection_cancel(bs, true);
     }
     if (qemu_in_coroutine()) {
@@ -685,8 +685,8 @@ static coroutine_fn void nbd_co_reconnect_loop(BDRVNBDState *s)
             }
             bdrv_inc_in_flight(s->bs);
         } else {
-            qemu_co_sleep_ns_wakeable(QEMU_CLOCK_REALTIME, timeout,
-                                      &s->connection_co_sleep_ns_state);
+            qemu_co_sleep_ns_wakeable(&s->reconnect_sleep,
+                                      QEMU_CLOCK_REALTIME, timeout);
             if (s->drained) {
                 continue;
             }

include/qemu/coroutine.h

@@ -291,21 +291,22 @@ void qemu_co_rwlock_wrlock(CoRwlock *lock);
  */
 void qemu_co_rwlock_unlock(CoRwlock *lock);
 
-typedef struct QemuCoSleepState QemuCoSleepState;
+typedef struct QemuCoSleep {
+    Coroutine *to_wake;
+} QemuCoSleep;
 
 /**
- * Yield the coroutine for a given duration. During this yield, @sleep_state
- * 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.
+ * Yield the coroutine for a given duration. Initializes @w so that,
+ * during this yield, it can be passed to qemu_co_sleep_wake() to
+ * terminate the sleep.
  */
-void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
-                                            QemuCoSleepState **sleep_state);
+void coroutine_fn qemu_co_sleep_ns_wakeable(QemuCoSleep *w,
+                                            QEMUClockType type, int64_t ns);
+
 static inline void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
 {
-    QemuCoSleepState *unused = NULL;
-    qemu_co_sleep_ns_wakeable(type, ns, &unused);
+    QemuCoSleep w = { 0 };
+    qemu_co_sleep_ns_wakeable(&w, type, ns);
 }
 
 /**
@@ -314,7 +315,7 @@ static inline void coroutine_fn qemu_co_sleep_ns(QEMUClockType type, int64_t ns)
  * qemu_co_sleep_ns() and should be checked to be non-NULL before calling
  * qemu_co_sleep_wake().
  */
-void qemu_co_sleep_wake(QemuCoSleepState *sleep_state);
+void qemu_co_sleep_wake(QemuCoSleep *w);
 
 /**
  * Yield until a file descriptor becomes readable

util/qemu-coroutine-sleep.c

@@ -19,55 +19,50 @@
 
 static const char *qemu_co_sleep_ns__scheduled = "qemu_co_sleep_ns";
 
-struct QemuCoSleepState {
+void qemu_co_sleep_wake(QemuCoSleep *w)
+{
     Coroutine *co;
-    QemuCoSleepState **user_state_pointer;
-};
 
-void qemu_co_sleep_wake(QemuCoSleepState *sleep_state)
-{
-    if (sleep_state) {
+    co = w->to_wake;
+    w->to_wake = NULL;
+    if (co) {
         /* Write of schedule protected by barrier write in aio_co_schedule */
-        const char *scheduled = qatomic_cmpxchg(&sleep_state->co->scheduled,
+        const char *scheduled = qatomic_cmpxchg(&co->scheduled,
                                                 qemu_co_sleep_ns__scheduled, NULL);
 
         assert(scheduled == qemu_co_sleep_ns__scheduled);
-        *sleep_state->user_state_pointer = NULL;
-        aio_co_wake(sleep_state->co);
+        aio_co_wake(co);
     }
 }
 
 static void co_sleep_cb(void *opaque)
 {
-    QemuCoSleepState **sleep_state = opaque;
-    qemu_co_sleep_wake(*sleep_state);
+    QemuCoSleep *w = opaque;
+    qemu_co_sleep_wake(w);
 }
 
-void coroutine_fn qemu_co_sleep_ns_wakeable(QEMUClockType type, int64_t ns,
-                                            QemuCoSleepState **sleep_state)
+void coroutine_fn qemu_co_sleep_ns_wakeable(QemuCoSleep *w,
+                                            QEMUClockType type, int64_t ns)
 {
+    Coroutine *co = qemu_coroutine_self();
     AioContext *ctx = qemu_get_current_aio_context();
     QEMUTimer ts;
-    QemuCoSleepState state = {
-        .co = qemu_coroutine_self(),
-        .user_state_pointer = sleep_state,
-    };
 
-    const char *scheduled = qatomic_cmpxchg(&state.co->scheduled, NULL,
-                                           qemu_co_sleep_ns__scheduled);
+    const char *scheduled = qatomic_cmpxchg(&co->scheduled, NULL,
+                                            qemu_co_sleep_ns__scheduled);
     if (scheduled) {
         fprintf(stderr,
                 "%s: Co-routine was already scheduled in '%s'\n",
                 __func__, scheduled);
         abort();
     }
 
-    aio_timer_init(ctx, &ts, type, SCALE_NS, co_sleep_cb, sleep_state);
-    *sleep_state = &state;
+    w->to_wake = co;
+    aio_timer_init(ctx, &ts, type, SCALE_NS, co_sleep_cb, w),
     timer_mod(&ts, qemu_clock_get_ns(type) + ns);
     qemu_coroutine_yield();
     timer_del(&ts);
 
-    /* qemu_co_sleep_wake clears *sleep_state before resuming this coroutine.  */
-    assert(*sleep_state == NULL);
+    /* w->to_wake is cleared before resuming this coroutine.  */
+    assert(w->to_wake == NULL);
 }