move aio queue allocation from io thread to submitting thread

since commit c9f415d7ea2dace5bf77f6518b6afc36bb7a5732, it has been
possible that the allocator is application-provided code, which cannot
necessarily run safely on io thread stacks, and which should not be
able to see the existence of io threads, since they are an
implementation detail.

instead of having the io thread request and possibly allocate its
queue (and the map structures leading to it), make the submitting
thread responsible for this, and pass the queue pointer into the io
thread via its args structure. this eliminates the only early error
case in io threads, making it no longer necessary to pass an error
status back to the submitting thread via the args structure.

src/aio/aio.c

@@ -41,13 +41,6 @@
  * blocked permanently.
  */
 
-struct aio_args {
-	struct aiocb *cb;
-	int op;
-	int err;
-	sem_t sem;
-};
-
 struct aio_thread {
 	pthread_t td;
 	struct aiocb *cb;
@@ -65,6 +58,13 @@ struct aio_queue {
 	struct aio_thread *head;
 };
 
+struct aio_args {
+	struct aiocb *cb;
+	struct aio_queue *q;
+	int op;
+	sem_t sem;
+};
+
 static pthread_rwlock_t maplock = PTHREAD_RWLOCK_INITIALIZER;
 static struct aio_queue *****map;
 static volatile int aio_fd_cnt;
@@ -196,12 +196,11 @@ static void *io_thread_func(void *ctx)
 	size_t len = cb->aio_nbytes;
 	off_t off = cb->aio_offset;
 
-	struct aio_queue *q = __aio_get_queue(fd, 1);
+	struct aio_queue *q = args->q;
 	ssize_t ret;
 
-	args->err = q ? 0 : EAGAIN;
+	pthread_mutex_lock(&q->lock);
 	sem_post(&args->sem);
-	if (!q) return 0;
 
 	at.op = op;
 	at.running = 1;
@@ -213,7 +212,6 @@ static void *io_thread_func(void *ctx)
 	at.prev = 0;
 	if ((at.next = q->head)) at.next->prev = &at;
 	q->head = &at;
-	q->ref++;
 
 	if (!q->init) {
 		int seekable = lseek(fd, 0, SEEK_CUR) >= 0;
@@ -272,9 +270,18 @@ static int submit(struct aiocb *cb, int op)
 	pthread_attr_t a;
 	sigset_t allmask, origmask;
 	pthread_t td;
-	struct aio_args args = { .cb = cb, .op = op };
+	struct aio_queue *q = __aio_get_queue(cb->aio_fildes, 1);
+	struct aio_args args = { .cb = cb, .op = op, .q = q };
 	sem_init(&args.sem, 0, 0);
 
+	if (!q) {
+		if (cb->aio_fildes < 0) errno = EBADF;
+		else errno = EAGAIN;
+		return -1;
+	}
+	q->ref++;
+	pthread_mutex_unlock(&q->lock);
+
 	if (cb->aio_sigevent.sigev_notify == SIGEV_THREAD) {
 		if (cb->aio_sigevent.sigev_notify_attributes)
 			a = *cb->aio_sigevent.sigev_notify_attributes;
@@ -291,6 +298,8 @@ static int submit(struct aiocb *cb, int op)
 	pthread_sigmask(SIG_BLOCK, &allmask, &origmask);
 	cb->__err = EINPROGRESS;
 	if (pthread_create(&td, &a, io_thread_func, &args)) {
+		pthread_mutex_lock(&q->lock);
+		__aio_unref_queue(q);
 		errno = EAGAIN;
 		ret = -1;
 	}
@@ -298,10 +307,6 @@ static int submit(struct aiocb *cb, int op)
 
 	if (!ret) {
 		while (sem_wait(&args.sem));
-		if (args.err) {
-			errno = args.err;
-			ret = -1;
-		}
 	}
 
 	return ret;