dm: add infrastructure for DAX support

Change mapped device to implement direct_access function,
dm_blk_direct_access(), which calls a target direct_access function.
'struct target_type' is extended to have target direct_access interface.
This function limits direct accessible size to the dm_target's limit
with max_io_len().

Add dm_table_supports_dax() to iterate all targets and associated block
devices to check for DAX support.  To add DAX support to a DM target the
target must only implement the direct_access function.

Add a new dm type, DM_TYPE_DAX_BIO_BASED, which indicates that mapped
device supports DAX and is bio based.  This new type is used to assure
that all target devices have DAX support and remain that way after
QUEUE_FLAG_DAX is set in mapped device.

At initial table load, QUEUE_FLAG_DAX is set to mapped device when setting
DM_TYPE_DAX_BIO_BASED to the type.  Any subsequent table load to the
mapped device must have the same type, or else it fails per the check in
table_load().

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 2ce339212b6e..b0db857f334b 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -26,6 +26,7 @@ struct bio_vec;
 #define DM_TYPE_BIO_BASED		1
 #define DM_TYPE_REQUEST_BASED		2
 #define DM_TYPE_MQ_REQUEST_BASED	3
+#define DM_TYPE_DAX_BIO_BASED		4
 
 typedef enum { STATUSTYPE_INFO, STATUSTYPE_TABLE } status_type_t;
 
@@ -124,6 +125,14 @@ typedef void (*dm_io_hints_fn) (struct dm_target *ti,
  */
 typedef int (*dm_busy_fn) (struct dm_target *ti);
 
+/*
+ * Returns:
+ *  < 0 : error
+ * >= 0 : the number of bytes accessible at the address
+ */
+typedef long (*dm_direct_access_fn) (struct dm_target *ti, sector_t sector,
+				     void __pmem **kaddr, pfn_t *pfn, long size);
+
 void dm_error(const char *message);
 
 struct dm_dev {
@@ -170,6 +179,7 @@ struct target_type {
 	dm_busy_fn busy;
 	dm_iterate_devices_fn iterate_devices;
 	dm_io_hints_fn io_hints;
+	dm_direct_access_fn direct_access;
 
 	/* For internal device-mapper use. */
 	struct list_head list;