iomap: advance the iter directly on zero range

Modify zero range to advance the iter directly. Replace the local pos
and length calculations with direct advances and loop based on iter
state instead.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20250207143253.314068-11-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/buffered-io.c

@@ -1341,17 +1341,16 @@ static inline int iomap_zero_iter_flush_and_stale(struct iomap_iter *i)
 
 static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 {
-	loff_t pos = iter->pos;
-	loff_t length = iomap_length(iter);
-	loff_t written = 0;
+	u64 bytes = iomap_length(iter);
+	int status;
 
 	do {
 		struct folio *folio;
-		int status;
 		size_t offset;
-		size_t bytes = min_t(u64, SIZE_MAX, length);
+		loff_t pos = iter->pos;
 		bool ret;
 
+		bytes = min_t(u64, SIZE_MAX, bytes);
 		status = iomap_write_begin(iter, pos, bytes, &folio);
 		if (status)
 			return status;
@@ -1372,14 +1371,14 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
 		if (WARN_ON_ONCE(!ret))
 			return -EIO;
 
-		pos += bytes;
-		length -= bytes;
-		written += bytes;
-	} while (length > 0);
+		status = iomap_iter_advance(iter, &bytes);
+		if (status)
+			break;
+	} while (bytes > 0);
 
 	if (did_zero)
 		*did_zero = true;
-	return written;
+	return status;
 }
 
 int
@@ -1433,11 +1432,14 @@ iomap_zero_range(struct inode *inode, loff_t pos, loff_t len, bool *did_zero,
 
 		if (srcmap->type == IOMAP_HOLE ||
 		    srcmap->type == IOMAP_UNWRITTEN) {
-			loff_t proc = iomap_length(&iter);
+			s64 proc;
 
 			if (range_dirty) {
 				range_dirty = false;
 				proc = iomap_zero_iter_flush_and_stale(&iter);
+			} else {
+				u64 length = iomap_length(&iter);
+				proc = iomap_iter_advance(&iter, &length);
 			}
 			iter.processed = proc;
 			continue;