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, 11 insertions, 0 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 2e9a3ca37bdd..31c2dc25886d 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1215,6 +1215,7 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
         struct hash_cell *hc;
         struct dm_table *t;
         struct mapped_device *md;
+        struct target_type *immutable_target_type;
 
         md = find_device(param);
         if (!md)
@@ -1230,6 +1231,16 @@ static int table_load(struct dm_ioctl *param, size_t param_size)
                 goto out;
         }
 
+        immutable_target_type = dm_get_immutable_target_type(md);
+        if (immutable_target_type &&
+            (immutable_target_type != dm_table_get_immutable_target_type(t))) {
+                DMWARN("can't replace immutable target type %s",
+                       immutable_target_type->name);
+                dm_table_destroy(t);
+                r = -EINVAL;
+                goto out;
+        }
+
         /* Protect md->type and md->queue against concurrent table loads. */
         dm_lock_md_type(md);
         if (dm_get_md_type(md) == DM_TYPE_NONE)