fs/dax: Remove unused size parameter

Passing size to copy_user_dax implies it can copy variable sizes of data
when in fact it calls copy_user_page() which is exactly a page.

We are safe because the only caller uses PAGE_SIZE anyway so just remove
the variable for clarity.

While we are at it change copy_user_dax() to copy_cow_page_dax() to make
it clear it is a singleton helper for this one case not implementing
what dax_iomap_actor() does.

Link: https://lore.kernel.org/r/20200717072056.73134-11-ira.weiny@intel.comReviewed-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

fs/dax.c

@@ -680,21 +680,20 @@ int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
 	return __dax_invalidate_entry(mapping, index, false);
 }
 
-static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
-		sector_t sector, size_t size, struct page *to,
-		unsigned long vaddr)
+static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_dev,
+			     sector_t sector, struct page *to, unsigned long vaddr)
 {
 	void *vto, *kaddr;
 	pgoff_t pgoff;
 	long rc;
 	int id;
 
-	rc = bdev_dax_pgoff(bdev, sector, size, &pgoff);
+	rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
 	if (rc)
 		return rc;
 
 	id = dax_read_lock();
-	rc = dax_direct_access(dax_dev, pgoff, PHYS_PFN(size), &kaddr, NULL);
+	rc = dax_direct_access(dax_dev, pgoff, PHYS_PFN(PAGE_SIZE), &kaddr, NULL);
 	if (rc < 0) {
 		dax_read_unlock(id);
 		return rc;
@@ -1305,8 +1304,8 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 			clear_user_highpage(vmf->cow_page, vaddr);
 			break;
 		case IOMAP_MAPPED:
-			error = copy_user_dax(iomap.bdev, iomap.dax_dev,
-					sector, PAGE_SIZE, vmf->cow_page, vaddr);
+			error = copy_cow_page_dax(iomap.bdev, iomap.dax_dev,
+						  sector, vmf->cow_page, vaddr);
 			break;
 		default:
 			WARN_ON_ONCE(1);