[PATCH 2/4] iomap: refactor an iomap_revalidate() helper

[Brian Foster <bfoster@redhat.com>]

The buffered write path revalidates the mapping on each folio lock
cycle. If the mapping has changed since the last lookup, the mapping
is marked stale and the operation must break back out into the
lookup path to update the mapping.

The zero range path will need to do something similar for correct
handling of dirty folios over unwritten ranges. Factor out the
validation callback into a new helper that marks the mapping stale
on failure.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/iomap/buffered-io.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index d46558990279..a9425170df72 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -756,6 +756,22 @@ static void __iomap_put_folio(struct iomap_iter *iter, loff_t pos, size_t ret,
 	}
 }
 
+/*
+ * Check whether the current mapping of the iter is still valid. If not, mark
+ * the mapping stale.
+ */
+static inline bool iomap_revalidate(struct iomap_iter *iter)
+{
+	const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;
+	bool iomap_valid = true;
+
+	if (folio_ops && folio_ops->iomap_valid)
+		iomap_valid = folio_ops->iomap_valid(iter->inode, &iter->iomap);
+	if (!iomap_valid)
+		iter->iomap.flags |= IOMAP_F_STALE;
+	return iomap_valid;
+}
+
 static int iomap_write_begin_inline(const struct iomap_iter *iter,
 		struct folio *folio)
 {
@@ -768,7 +784,6 @@ static int iomap_write_begin_inline(const struct iomap_iter *iter,
 static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 		size_t len, struct folio **foliop)
 {
-	const struct iomap_folio_ops *folio_ops = iter->iomap.folio_ops;
 	const struct iomap *srcmap = iomap_iter_srcmap(iter);
 	struct folio *folio;
 	int status = 0;
@@ -797,15 +812,8 @@ static int iomap_write_begin(struct iomap_iter *iter, loff_t pos,
 	 * could do the wrong thing here (zero a page range incorrectly or fail
 	 * to zero) and corrupt data.
 	 */
-	if (folio_ops && folio_ops->iomap_valid) {
-		bool iomap_valid = folio_ops->iomap_valid(iter->inode,
-							 &iter->iomap);
-		if (!iomap_valid) {
-			iter->iomap.flags |= IOMAP_F_STALE;
-			status = 0;
-			goto out_unlock;
-		}
-	}
+	if (!iomap_revalidate(iter))
+		goto out_unlock;
 
 	if (pos + len > folio_pos(folio) + folio_size(folio))
 		len = folio_pos(folio) + folio_size(folio) - pos;
-- 
2.45.0