WIP : Do more syncing when kstat.zfs.darwin.tunable.use_system_sync != 0

module/os/macos/spl/spl-taskq.c

@@ -1684,7 +1684,10 @@ taskq_empty(taskq_t *tq)
 int
 taskq_empty_ent(taskq_ent_t *t)
 {
-	return (IS_EMPTY(*t));
+	if (t->tqent_prev == NULL && t->tqent_next == NULL)
+		return (TRUE);
+	else
+		return (IS_EMPTY(*t));
 }
 
 /*

module/os/macos/zfs/ldi_iokit.cpp

@@ -423,17 +423,19 @@ handle_sync_iokit(struct ldi_handle *lhp)
 
 #if defined(MAC_OS_X_VERSION_10_11) &&        \
 	(MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_11)
+	/* from module/os/macos/zfs/zfs_vfsops.c */
+	extern uint64_t zfs_vfs_sync_paranoia;
 	/* Issue device sync */
-	if (LH_MEDIA(lhp)->synchronize(LH_CLIENT(lhp), 0, 0, kIOStorageSynchronizeOptionBarrier) !=
-	    kIOReturnSuccess) {
-		printf("%s %s\n", __func__,
-		    "IOMedia synchronizeCache (with write barrier) failed\n");
-		if (LH_MEDIA(lhp)->synchronize(LH_CLIENT(lhp), 0, 0, 0) !=
-		    kIOReturnSuccess) {
-			printf("%s %s\n", __func__,
-			    "IOMedia synchronizeCache (standard) failed\n");
-			return (ENOTSUP);
-		}
+	IOStorageSynchronizeOptions synctype = (zfs_vfs_sync_paranoia != 0)
+	    ? kIOStorageSynchronizeOptionNone
+	    : kIOStorageSynchronizeOptionBarrier;
+	IOReturn ret = LH_MEDIA(lhp)->synchronize(LH_CLIENT(lhp),
+	    0, 0, synctype);
+	if (ret !=  kIOReturnSuccess) {
+		printf("%s %s %d %s\n", __func__,
+		    "IOMedia synchronizeCache (with write barrier) failed",
+		    ret, "(see IOReturn.h)\n");
+		return (ENOTSUP);
 	}
 #else
 	/* Issue device sync */

module/os/macos/zfs/vdev_disk.c

@@ -53,6 +53,8 @@ static void vdev_disk_close(vdev_t *);
 
 extern unsigned int spl_split_stack_below;
 
+extern uint64_t zfs_vfs_sync_paranoia;
+
 typedef struct vdev_disk_ldi_cb {
 	list_node_t		lcb_next;
 	ldi_callback_id_t	lcb_id;
@@ -517,10 +519,13 @@ vdev_disk_io_strategy(void *arg)
 	switch (zio->io_type) {
 
 	case ZIO_TYPE_WRITE:
-		if (zio->io_priority == ZIO_PRIORITY_SYNC_WRITE)
+		if (zio->io_priority == ZIO_PRIORITY_SYNC_WRITE) {
 			flags = B_WRITE;
-		else
+			if (zfs_vfs_sync_paranoia != 0)
+				flags |= B_FUA;
+		} else {
 			flags = B_WRITE | B_ASYNC;
+		}
 
 		bp->b_un.b_addr =
 		    abd_borrow_buf_copy(zio->io_abd, zio->io_size);

module/os/macos/zfs/zfs_vfsops.c

@@ -129,7 +129,7 @@ zfs_is_readonly(zfsvfs_t *zfsvfs)
  * syncs. (As per illumos) Unfortunately, we can not tell the difference
  * of when users run "sync" by hand. Sync is called on umount though.
  */
-uint64_t zfs_vfs_sync_paranoia = 0;
+uint64_t zfs_vfs_sync_paranoia = 1;
 
 int
 zfs_vfs_sync(struct mount *vfsp, __unused int waitfor,

tests/zfs-tests/cmd/librt/mach_gettime.c

@@ -12,6 +12,8 @@
 #include <mach/clock.h>
 #include <mach/mach_time.h>
 
+void gettime_dummy(void);
+
 extern int
 clock_gettime(clock_id_t clock_id, struct timespec *tp);