dax: introduce dax_operations

Track a set of dax_operations per dax_device that can be set at
alloc_dax() time. These operations will be used to stop the abuse of
block_device_operations for communicating dax capabilities to
filesystems. It will also be used to replace the "pmem api" and move
pmem-specific cache maintenance, and other dax-driver-specific
filesystem-dax operations, to dax device methods. In particular this
allows us to stop abusing __copy_user_nocache(), via memcpy_to_pmem(),
with a driver specific replacement.

This is a standalone introduction of the operations. Follow on patches
convert each dax-driver and teach fs/dax.c to use ->direct_access() from
dax_operations instead of block_device_operations.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/dax/dax.h b/drivers/dax/dax.h
index 246a24d68d4c..617bbc24be2b 100644
--- a/drivers/dax/dax.h
+++ b/drivers/dax/dax.h
@@ -13,7 +13,9 @@
 #ifndef __DAX_H__
 #define __DAX_H__
 struct dax_device;
-struct dax_device *alloc_dax(void *private, const char *host);
+struct dax_operations;
+struct dax_device *alloc_dax(void *private, const char *host,
+                const struct dax_operations *ops);
 void put_dax(struct dax_device *dax_dev);
 bool dax_alive(struct dax_device *dax_dev);
 void kill_dax(struct dax_device *dax_dev);