filesystem-dax: convert to dax_direct_access()

Now that a dax_device is plumbed through all dax-capable drivers we can
switch from block_device_operations to dax_operations for invoking
->direct_access.

This also lets us kill off some usages of struct blk_dax_ctl on the way
to its eventual removal.
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

fs/iomap.c

@@ -360,7 +360,8 @@ static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
 	sector_t sector = iomap->blkno +
 		(((pos & ~(PAGE_SIZE - 1)) - iomap->offset) >> 9);
 
-	return __dax_zero_page_range(iomap->bdev, sector, offset, bytes);
+	return __dax_zero_page_range(iomap->bdev, iomap->dax_dev, sector,
+			offset, bytes);
 }
 
 static loff_t

include/linux/dax.h

@@ -70,11 +70,13 @@ void dax_wake_mapping_entry_waiter(struct address_space *mapping,
 		pgoff_t index, void *entry, bool wake_all);
 
 #ifdef CONFIG_FS_DAX
-int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
+int __dax_zero_page_range(struct block_device *bdev,
+		struct dax_device *dax_dev, sector_t sector,
 		unsigned int offset, unsigned int length);
 #else
 static inline int __dax_zero_page_range(struct block_device *bdev,
-		sector_t sector, unsigned int offset, unsigned int length)
+		struct dax_device *dax_dev, sector_t sector,
+		unsigned int offset, unsigned int length)
 {
 	return -ENXIO;
 }