fsdax: add dax_iomap_cow_copy() for dax zero

Punch hole on a reflinked file needs dax_iomap_cow_copy() too.  Otherwise,
data in not aligned area will be not correct.  So, add the CoW operation
for not aligned case in dax_memzero().

Link: https://lkml.kernel.org/r/20220603053738.1218681-12-ruansy.fnst@fujitsu.comSigned-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.wiliams@intel.com>
Cc: Dan Williams <dan.j.williams@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

@@ -1221,17 +1221,28 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
 }
 #endif /* CONFIG_FS_DAX_PMD */
 
-static int dax_memzero(struct dax_device *dax_dev, pgoff_t pgoff,
-		unsigned int offset, size_t size)
+static int dax_memzero(struct iomap_iter *iter, loff_t pos, size_t size)
 {
+	const struct iomap *iomap = &iter->iomap;
+	const struct iomap *srcmap = iomap_iter_srcmap(iter);
+	unsigned offset = offset_in_page(pos);
+	pgoff_t pgoff = dax_iomap_pgoff(iomap, pos);
 	void *kaddr;
 	long ret;
 
-	ret = dax_direct_access(dax_dev, pgoff, 1, DAX_ACCESS, &kaddr, NULL);
-	if (ret > 0) {
-		memset(kaddr + offset, 0, size);
-		dax_flush(dax_dev, kaddr + offset, size);
-	}
+	ret = dax_direct_access(iomap->dax_dev, pgoff, 1, DAX_ACCESS, &kaddr,
+				NULL);
+	if (ret < 0)
+		return ret;
+	memset(kaddr + offset, 0, size);
+	if (srcmap->addr != iomap->addr) {
+		ret = dax_iomap_cow_copy(pos, size, PAGE_SIZE, srcmap,
+					 kaddr);
+		if (ret < 0)
+			return ret;
+		dax_flush(iomap->dax_dev, kaddr, PAGE_SIZE);
+	} else
+		dax_flush(iomap->dax_dev, kaddr + offset, size);
 	return ret;
 }
 
@@ -1258,7 +1269,7 @@ static s64 dax_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		if (IS_ALIGNED(pos, PAGE_SIZE) && size == PAGE_SIZE)
 			rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
 		else
-			rc = dax_memzero(iomap->dax_dev, pgoff, offset, size);
+			rc = dax_memzero(iter, pos, size);
 		dax_read_unlock(id);
 
 		if (rc < 0)