[PATCH RFC 1/4] dev_dax_iomap: Add add_dax_ops() func for fs-dax to provide dax holder_ops

["John Groves" <john@jagalactic.com>]

From: John Groves <john@groves.net>

This is clearly not the right way to set the holder_ops; where &
how should this be done?
---
 drivers/dax/super.c | 16 ++++++++++++++++
 include/linux/dax.h |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 0da9232ea175..3d4e205c1854 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -467,6 +467,22 @@ struct dax_device *alloc_dax(void *private, const struct dax_operations *ops)
 }
 EXPORT_SYMBOL_GPL(alloc_dax);
 
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+/* famfs calls this to add the holder_ops. There is probably a more elegant approach */
+int add_dax_ops(
+	struct dax_device           *dax_dev,
+	const struct dax_holder_operations *hops)
+{
+	/* dax_dev->ops should have been populated by devm_create_dev_dax() */
+	WARN_ON(!dax_dev->ops);
+
+	/* Use cmpxchg? */
+	dax_dev->holder_ops = hops;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(add_dax_ops);
+#endif /* DEV_DAX_IOMAP */
+
 void put_dax(struct dax_device *dax_dev)
 {
 	if (!dax_dev)
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b463502b16e1..31b68667b3cb 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -57,6 +57,11 @@ struct dax_holder_operations {
 
 #if IS_ENABLED(CONFIG_DAX)
 struct dax_device *alloc_dax(void *private, const struct dax_operations *ops);
+
+#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP)
+int add_dax_ops(struct dax_device *dax_dev,
+		const struct dax_holder_operations *hops);
+#endif
 void *dax_holder(struct dax_device *dax_dev);
 void put_dax(struct dax_device *dax_dev);
 void kill_dax(struct dax_device *dax_dev);
-- 
2.40.1