dax: advance the iomap_iter on unshare range

Advance the iter and return 0 or an error code for success or
failure.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20250224144757.237706-8-bfoster@redhat.com
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Brian Foster

fs/dax.c

@@ -1266,11 +1266,11 @@ static s64 dax_unshare_iter(struct iomap_iter *iter)
 	u64 copy_len = iomap_length(iter);
 	u32 mod;
 	int id = 0;
-	s64 ret = 0;
+	s64 ret = iomap_length(iter);
 	void *daddr = NULL, *saddr = NULL;
 
 	if (!iomap_want_unshare_iter(iter))
-		return iomap_length(iter);
+		return iomap_iter_advance(iter, &ret);
 
 	/*
 	 * Extend the file range to be aligned to fsblock/pagesize, because
@@ -1307,7 +1307,9 @@ static s64 dax_unshare_iter(struct iomap_iter *iter)
 
 out_unlock:
 	dax_read_unlock(id);
-	return dax_mem2blk_err(ret);
+	if (ret < 0)
+		return dax_mem2blk_err(ret);
+	return iomap_iter_advance(iter, &ret);
 }
 
 int dax_file_unshare(struct inode *inode, loff_t pos, loff_t len,