iomap: lift error code check out of iomap_iter_advance()

The error code is only used to check whether iomap_iter() should
terminate due to an error returned in iter.processed. Lift the check
out of iomap_iter_advance() in preparation to make it more generic.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20250207143253.314068-5-bfoster@redhat.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Brian Foster

fs/iomap/iter.c

@@ -30,8 +30,6 @@ static inline int iomap_iter_advance(struct iomap_iter *iter, s64 count)
 	bool stale = iter->iomap.flags & IOMAP_F_STALE;
 	int ret = 1;
 
-	if (count < 0)
-		return count;
 	if (WARN_ON_ONCE(count > iomap_length(iter)))
 		return -EIO;
 	iter->pos += count;
@@ -71,6 +69,7 @@ static inline void iomap_iter_done(struct iomap_iter *iter)
  */
 int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 {
+	s64 processed;
 	int ret;
 
 	trace_iomap_iter(iter, ops, _RET_IP_);
@@ -86,8 +85,14 @@ int iomap_iter(struct iomap_iter *iter, const struct iomap_ops *ops)
 			return ret;
 	}
 
+	processed = iter->processed;
+	if (processed < 0) {
+		iomap_iter_reset_iomap(iter);
+		return processed;
+	}
+
 	/* advance and clear state from the previous iteration */
-	ret = iomap_iter_advance(iter, iter->processed);
+	ret = iomap_iter_advance(iter, processed);
 	iomap_iter_reset_iomap(iter);
 	if (ret <= 0)
 		return ret;