iomap: reset per-iter state on non-error iter advances

iomap_iter_advance() zeroes the processed and mapping fields on
every non-error iteration except for the last expected iteration
(i.e. return 0 expected to terminate the iteration loop). This
appears to be circumstantial as nothing currently relies on these
fields after the final iteration.

Therefore to better faciliate iomap_iter reuse in subsequent
patches, update iomap_iter_advance() to always reset per-iteration
state on successful completion.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20241115200155.593665-2-bfoster@redhat.com
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Brian Foster

fs/iomap/iter.c

@@ -22,26 +22,25 @@
 static inline int iomap_iter_advance(struct iomap_iter *iter)
 {
 	bool stale = iter->iomap.flags & IOMAP_F_STALE;
+	int ret = 1;
 
 	/* handle the previous iteration (if any) */
 	if (iter->iomap.length) {
 		if (iter->processed < 0)
 			return iter->processed;
-		if (!iter->processed && !stale)
-			return 0;
 		if (WARN_ON_ONCE(iter->processed > iomap_length(iter)))
 			return -EIO;
 		iter->pos += iter->processed;
 		iter->len -= iter->processed;
-		if (!iter->len)
-			return 0;
+		if (!iter->len || (!iter->processed && !stale))
+			ret = 0;
 	}
 
-	/* clear the state for the next iteration */
+	/* clear the per iteration state */
 	iter->processed = 0;
 	memset(&iter->iomap, 0, sizeof(iter->iomap));
 	memset(&iter->srcmap, 0, sizeof(iter->srcmap));
-	return 1;
+	return ret;
 }
 
 static inline void iomap_iter_done(struct iomap_iter *iter)