dm: allow targets to return output from messages they are sent

Could be useful for a target to return stats or other information.
If a target does DMEMIT() anything to @result from its .message method
then it must return 1 to the caller.
Signed-off-By: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-cache-target.c

@@ -3387,7 +3387,8 @@ static int process_invalidate_cblocks_message(struct cache *cache, unsigned coun
  *
  * The key migration_threshold is supported by the cache target core.
  */
-static int cache_message(struct dm_target *ti, unsigned argc, char **argv)
+static int cache_message(struct dm_target *ti, unsigned argc, char **argv,
+			 char *result, unsigned maxlen)
 {
 	struct cache *cache = ti->private;
 

drivers/md/dm-crypt.c

@@ -2942,7 +2942,8 @@ static void crypt_resume(struct dm_target *ti)
  *	key set <key>
  *	key wipe
  */
-static int crypt_message(struct dm_target *ti, unsigned argc, char **argv)
+static int crypt_message(struct dm_target *ti, unsigned argc, char **argv,
+			 char *result, unsigned maxlen)
 {
 	struct crypt_config *cc = ti->private;
 	int key_size, ret = -EINVAL;

drivers/md/dm-era-target.c

@@ -1635,7 +1635,8 @@ static void era_status(struct dm_target *ti, status_type_t type,
 	DMEMIT("Error");
 }
 
-static int era_message(struct dm_target *ti, unsigned argc, char **argv)
+static int era_message(struct dm_target *ti, unsigned argc, char **argv,
+		       char *result, unsigned maxlen)
 {
 	struct era *era = ti->private;
 

drivers/md/dm-ioctl.c

@@ -1595,7 +1595,7 @@ static int target_message(struct file *filp, struct dm_ioctl *param, size_t para
 		DMWARN("Target message sector outside device.");
 		r = -EINVAL;
 	} else if (ti->type->message)
-		r = ti->type->message(ti, argc, argv);
+		r = ti->type->message(ti, argc, argv, result, maxlen);
 	else {
 		DMWARN("Target type does not support messages");
 		r = -EINVAL;

drivers/md/dm-log-writes.c

@@ -887,7 +887,8 @@ static int log_writes_iterate_devices(struct dm_target *ti,
  * Messages supported:
  *   mark <mark data> - specify the marked data.
  */
-static int log_writes_message(struct dm_target *ti, unsigned argc, char **argv)
+static int log_writes_message(struct dm_target *ti, unsigned argc, char **argv,
+			      char *result, unsigned maxlen)
 {
 	int r = -EINVAL;
 	struct log_writes_c *lc = ti->private;

drivers/md/dm-mpath.c

@@ -1811,7 +1811,8 @@ static void multipath_status(struct dm_target *ti, status_type_t type,
 	spin_unlock_irqrestore(&m->lock, flags);
 }
 
-static int multipath_message(struct dm_target *ti, unsigned argc, char **argv)
+static int multipath_message(struct dm_target *ti, unsigned argc, char **argv,
+			     char *result, unsigned maxlen)
 {
 	int r = -EINVAL;
 	struct dm_dev *dev;

drivers/md/dm-raid.c

@@ -3663,7 +3663,8 @@ static void raid_status(struct dm_target *ti, status_type_t type,
 	}
 }
 
-static int raid_message(struct dm_target *ti, unsigned int argc, char **argv)
+static int raid_message(struct dm_target *ti, unsigned int argc, char **argv,
+			char *result, unsigned maxlen)
 {
 	struct raid_set *rs = ti->private;
 	struct mddev *mddev = &rs->md;

drivers/md/dm-switch.c

@@ -466,7 +466,8 @@ static int process_set_region_mappings(struct switch_ctx *sctx,
  *
  * Only set_region_mappings is supported.
  */
-static int switch_message(struct dm_target *ti, unsigned argc, char **argv)
+static int switch_message(struct dm_target *ti, unsigned argc, char **argv,
+			  char *result, unsigned maxlen)
 {
 	static DEFINE_MUTEX(message_mutex);
 

drivers/md/dm-thin.c

@@ -3705,7 +3705,8 @@ static int process_release_metadata_snap_mesg(unsigned argc, char **argv, struct
  *   reserve_metadata_snap
  *   release_metadata_snap
  */
-static int pool_message(struct dm_target *ti, unsigned argc, char **argv)
+static int pool_message(struct dm_target *ti, unsigned argc, char **argv,
+			char *result, unsigned maxlen)
 {
 	int r = -EINVAL;
 	struct pool_c *pt = ti->private;

include/linux/device-mapper.h

@@ -87,7 +87,8 @@ typedef void (*dm_resume_fn) (struct dm_target *ti);
 typedef void (*dm_status_fn) (struct dm_target *ti, status_type_t status_type,
 			      unsigned status_flags, char *result, unsigned maxlen);
 
-typedef int (*dm_message_fn) (struct dm_target *ti, unsigned argc, char **argv);
+typedef int (*dm_message_fn) (struct dm_target *ti, unsigned argc, char **argv,
+			      char *result, unsigned maxlen);
 
 typedef int (*dm_prepare_ioctl_fn) (struct dm_target *ti,
 			    struct block_device **bdev, fmode_t *mode);

include/uapi/linux/dm-ioctl.h

@@ -270,9 +270,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY	_IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR	4
-#define DM_VERSION_MINOR	37
+#define DM_VERSION_MINOR	38
 #define DM_VERSION_PATCHLEVEL	0
-#define DM_VERSION_EXTRA	"-ioctl (2017-09-20)"
+#define DM_VERSION_EXTRA	"-ioctl (2018-02-28)"
 
 /* Status bits */
 #define DM_READONLY_FLAG	(1 << 0) /* In/Out */