dm log: add flush callback fn

Introduce a callback pointer from the log to dm-raid1 layer.

Before some region is set as "in-sync", we need to flush hardware cache on
all the disks. But the log module doesn't have access to the mirror_set
structure. So it will use this callback.

So far the callback is unused, it will be used in further patches.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-log.c

@@ -146,6 +146,7 @@ EXPORT_SYMBOL(dm_dirty_log_type_unregister);
 
 struct dm_dirty_log *dm_dirty_log_create(const char *type_name,
 			struct dm_target *ti,
+			int (*flush_callback_fn)(struct dm_target *ti),
 			unsigned int argc, char **argv)
 {
 	struct dm_dirty_log_type *type;
@@ -161,6 +162,7 @@ struct dm_dirty_log *dm_dirty_log_create(const char *type_name,
 		return NULL;
 	}
 
+	log->flush_callback_fn = flush_callback_fn;
 	log->type = type;
 	if (type->ctr(log, ti, argc, argv)) {
 		kfree(log);

drivers/md/dm-raid1.c

@@ -896,7 +896,7 @@ static struct dm_dirty_log *create_dirty_log(struct dm_target *ti,
 		return NULL;
 	}
 
-	dl = dm_dirty_log_create(argv[0], ti, param_count, argv + 2);
+	dl = dm_dirty_log_create(argv[0], ti, NULL, param_count, argv + 2);
 	if (!dl) {
 		ti->error = "Error creating mirror dirty log";
 		return NULL;

include/linux/dm-dirty-log.h

@@ -21,6 +21,7 @@ struct dm_dirty_log_type;
 
 struct dm_dirty_log {
 	struct dm_dirty_log_type *type;
+	int (*flush_callback_fn)(struct dm_target *ti);
 	void *context;
 };
 
@@ -137,6 +138,7 @@ int dm_dirty_log_type_unregister(struct dm_dirty_log_type *type);
  */
 struct dm_dirty_log *dm_dirty_log_create(const char *type_name,
 			struct dm_target *ti,
+			int (*flush_callback_fn)(struct dm_target *ti),
 			unsigned argc, char **argv);
 void dm_dirty_log_destroy(struct dm_dirty_log *log);