[PATCH V4 17/19] famfs_fuse: Add DAX address_space_operations with noop_dirty_folio

[John Groves <John@Groves.net>]

From: John Groves <John@Groves.net>

Famfs is memory-backed; there is no place to write back to, and no
reason to mark pages dirty at all.

Signed-off-by: John Groves <john@groves.net>
---
 fs/fuse/famfs.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
index ee3526175b6b..f98e358ea489 100644
--- a/fs/fuse/famfs.c
+++ b/fs/fuse/famfs.c
@@ -14,6 +14,7 @@
 #include <linux/mm.h>
 #include <linux/dax.h>
 #include <linux/iomap.h>
+#include <linux/pagemap.h>
 #include <linux/path.h>
 #include <linux/namei.h>
 #include <linux/string.h>
@@ -39,6 +40,15 @@ static const struct dax_holder_operations famfs_fuse_dax_holder_ops = {
 	.notify_failure		= famfs_dax_notify_failure,
 };
 
+/*
+ * DAX address_space_operations for famfs.
+ * famfs doesn't need dirty tracking - writes go directly to
+ * memory with no writeback required.
+ */
+static const struct address_space_operations famfs_dax_aops = {
+	.dirty_folio	= noop_dirty_folio,
+};
+
 /*****************************************************************************/
 
 /*
@@ -625,6 +635,7 @@ famfs_file_init_dax(
 		}
 		i_size_write(inode, meta->file_size);
 		inode->i_flags |= S_DAX;
+		inode->i_data.a_ops = &famfs_dax_aops;
 	}
  unlock_out:
 	inode_unlock(inode);
-- 
2.52.0