fsdax: output address in dax_iomap_pfn() and rename it

Add address output in dax_iomap_pfn() in order to perform a memcpy() in
CoW case.  Since this function both output address and pfn, rename it to
dax_iomap_direct_access().

[ruansy.fnst@fujitsu.com: initialize `rc', per Dan]
  Link: https://lore.kernel.org/linux-fsdevel/Yp8FUZnO64Qvyx5G@kili/
  Link: https://lkml.kernel.org/r/20220607143837.161174-1-ruansy.fnst@fujitsu.com
Link: https://lkml.kernel.org/r/20220603053738.1218681-9-ruansy.fnst@fujitsu.comSigned-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.wiliams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.com>
Cc: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/dax.c

@@ -1026,20 +1026,22 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 }
 EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
 
-static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
-			 pfn_t *pfnp)
+static int dax_iomap_direct_access(const struct iomap *iomap, loff_t pos,
+		size_t size, void **kaddr, pfn_t *pfnp)
 {
 	pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
-	int id, rc;
+	int id, rc = 0;
 	long length;
 
 	id = dax_read_lock();
 	length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
-				   DAX_ACCESS, NULL, pfnp);
+				   DAX_ACCESS, kaddr, pfnp);
 	if (length < 0) {
 		rc = length;
 		goto out;
 	}
+	if (!pfnp)
+		goto out_check_addr;
 	rc = -EINVAL;
 	if (PFN_PHYS(length) < size)
 		goto out;
@@ -1049,6 +1051,12 @@ static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
 	if (length > 1 && !pfn_t_devmap(*pfnp))
 		goto out;
 	rc = 0;
+
+out_check_addr:
+	if (!kaddr)
+		goto out;
+	if (!*kaddr)
+		rc = -EFAULT;
 out:
 	dax_read_unlock(id);
 	return rc;
@@ -1456,7 +1464,7 @@ static vm_fault_t dax_fault_iter(struct vm_fault *vmf,
 		return pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
 	}
 
-	err = dax_iomap_pfn(&iter->iomap, pos, size, &pfn);
+	err = dax_iomap_direct_access(&iter->iomap, pos, size, NULL, &pfn);
 	if (err)
 		return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);