dm table: add immutable feature

Introduce DM_TARGET_IMMUTABLE to indicate that the target type cannot be mixed
with any other target type, and once loaded into a device, it cannot be
replaced with a table containing a different type.

The thin provisioning pool device will use this.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2fe3017ba97..9836324e211 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -140,6 +140,8 @@ struct mapped_device {
 	/* Protect queue and type against concurrent access. */
 	struct mutex type_lock;
 
+	struct target_type *immutable_target_type;
+
 	struct gendisk *disk;
 	char name[16];
 
@@ -2096,6 +2098,8 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
 	write_lock_irqsave(&md->map_lock, flags);
 	old_map = md->map;
 	md->map = t;
+	md->immutable_target_type = dm_table_get_immutable_target_type(t);
+
 	dm_table_set_restrictions(t, q, limits);
 	if (merge_is_optional)
 		set_bit(DMF_MERGE_IS_OPTIONAL, &md->flags);
@@ -2166,6 +2170,11 @@ unsigned dm_get_md_type(struct mapped_device *md)
 	return md->type;
 }
 
+struct target_type *dm_get_immutable_target_type(struct mapped_device *md)
+{
+	return md->immutable_target_type;
+}
+
 /*
  * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
  */