iomap: move the direct IO code into a separate file

Move the direct IO code into a separate file so that we can group
related functions in a single file instead of having a single enormous
source file.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

include/linux/iomap.h

@@ -7,6 +7,7 @@
 #include <linux/mm.h>
 #include <linux/types.h>
 #include <linux/mm_types.h>
+#include <linux/blkdev.h>
 
 struct address_space;
 struct fiemap_extent_info;
@@ -69,6 +70,12 @@ struct iomap {
 	const struct iomap_page_ops *page_ops;
 };
 
+static inline sector_t
+iomap_sector(struct iomap *iomap, loff_t pos)
+{
+	return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
+}
+
 /*
  * When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
  * and page_done will be called for each page written to.  This only applies to