[PATCH 1/2] iomap: add iomap_writepages_unbound() to write beyond EOF

[Andrey Albershteyn <aalbersh@xxxxxxxxxx>]

From: Andrey Albershteyn <aalbersh@xxxxxxxxxx>

Add iomap_writepages_unbound() without limit in form of EOF. XFS
will use this to writeback extended attributes (fs-verity Merkle
tree) in range far beyond EOF.

Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 55 ++++++++++++++++++++++++++++++++----------
 include/linux/iomap.h  |  4 +++
 2 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 955f19e27e47..61ec924c5b80 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -979,13 +979,13 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
 		 * unlock and release the folio.
 		 */
 		old_size = iter->inode->i_size;
-		if (pos + written > old_size) {
+		if (!(iter->flags & IOMAP_NOSIZE) && (pos + written > old_size)) {
 			i_size_write(iter->inode, pos + written);
 			iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
 		}
 		__iomap_put_folio(iter, pos, written, folio);
 
-		if (old_size < pos)
+		if (!(iter->flags & IOMAP_NOSIZE) && (old_size < pos))
 			pagecache_isize_extended(iter->inode, old_size, pos);
 
 		cond_resched();
@@ -1918,18 +1918,10 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	int error = 0;
 	u32 rlen;
 
-	WARN_ON_ONCE(!folio_test_locked(folio));
-	WARN_ON_ONCE(folio_test_dirty(folio));
-	WARN_ON_ONCE(folio_test_writeback(folio));
-
-	trace_iomap_writepage(inode, pos, folio_size(folio));
-
-	if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
-		folio_unlock(folio);
-		return 0;
-	}
 	WARN_ON_ONCE(end_pos <= pos);
 
+	trace_iomap_writepage(inode, pos, folio_size(folio));
+
 	if (i_blocks_per_folio(inode, folio) > 1) {
 		if (!ifs) {
 			ifs = ifs_alloc(inode, folio, 0);
@@ -1992,6 +1984,23 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	return error;
 }
 
+/* Map pages bound by EOF */
+static int iomap_writepage_map_eof(struct iomap_writepage_ctx *wpc,
+		struct writeback_control *wbc, struct folio *folio)
+{
+	int error;
+	struct inode *inode = folio->mapping->host;
+	u64 end_pos = folio_pos(folio) + folio_size(folio);
+
+	if (!iomap_writepage_handle_eof(folio, inode, &end_pos)) {
+		folio_unlock(folio);
+		return 0;
+	}
+
+	error = iomap_writepage_map(wpc, wbc, folio);
+	return error;
+}
+
 int
 iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
 		struct iomap_writepage_ctx *wpc,
@@ -2008,12 +2017,32 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
 			PF_MEMALLOC))
 		return -EIO;
 
+	wpc->ops = ops;
+	while ((folio = writeback_iter(mapping, wbc, folio, &error))) {
+		WARN_ON_ONCE(!folio_test_locked(folio));
+		WARN_ON_ONCE(folio_test_dirty(folio));
+		WARN_ON_ONCE(folio_test_writeback(folio));
+
+		error = iomap_writepage_map_eof(wpc, wbc, folio);
+	}
+	return iomap_submit_ioend(wpc, error);
+}
+EXPORT_SYMBOL_GPL(iomap_writepages);
+
+int
+iomap_writepages_unbound(struct address_space *mapping, struct writeback_control *wbc,
+		struct iomap_writepage_ctx *wpc,
+		const struct iomap_writeback_ops *ops)
+{
+	struct folio *folio = NULL;
+	int error;
+
 	wpc->ops = ops;
 	while ((folio = writeback_iter(mapping, wbc, folio, &error)))
 		error = iomap_writepage_map(wpc, wbc, folio);
 	return iomap_submit_ioend(wpc, error);
 }
-EXPORT_SYMBOL_GPL(iomap_writepages);
+EXPORT_SYMBOL_GPL(iomap_writepages_unbound);
 
 static int __init iomap_buffered_init(void)
 {
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 5675af6b740c..3bfd3035ac28 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -181,6 +181,7 @@ struct iomap_folio_ops {
 #define IOMAP_DAX		(1 << 8) /* DAX mapping */
 #else
 #define IOMAP_DAX		0
+#define IOMAP_NOSIZE		(1 << 9) /* Don't update in-memory inode size*/
 #endif /* CONFIG_FS_DAX */
 #define IOMAP_ATOMIC		(1 << 9)
 
@@ -390,6 +391,9 @@ void iomap_sort_ioends(struct list_head *ioend_list);
 int iomap_writepages(struct address_space *mapping,
 		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
 		const struct iomap_writeback_ops *ops);
+int iomap_writepages_unbound(struct address_space *mapping,
+		struct writeback_control *wbc, struct iomap_writepage_ctx *wpc,
+		const struct iomap_writeback_ops *ops);
 
 /*
  * Flags for direct I/O ->end_io:
-- 
2.47.0