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, 21 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9917141729ef..8e9132130142 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -54,6 +54,7 @@ struct dm_table {
         sector_t *highs;
         struct dm_target *targets;
 
+        struct target_type *immutable_target_type;
         unsigned integrity_supported:1;
         unsigned singleton:1;
 
@@ -780,6 +781,21 @@ int dm_table_add_target(struct dm_table *t, const char *type,
                 return -EINVAL;
         }
 
+        if (t->immutable_target_type) {
+                if (t->immutable_target_type != tgt->type) {
+                        DMERR("%s: immutable target type %s cannot be mixed with other target types",
+                              dm_device_name(t->md), t->immutable_target_type->name);
+                        return -EINVAL;
+                }
+        } else if (dm_target_is_immutable(tgt->type)) {
+                if (t->num_targets) {
+                        DMERR("%s: immutable target type %s cannot be mixed with other target types",
+                              dm_device_name(t->md), tgt->type->name);
+                        return -EINVAL;
+                }
+                t->immutable_target_type = tgt->type;
+        }
+
         tgt->table = t;
         tgt->begin = start;
         tgt->len = len;
@@ -937,6 +953,11 @@ unsigned dm_table_get_type(struct dm_table *t)
         return t->type;
 }
 
+struct target_type *dm_table_get_immutable_target_type(struct dm_table *t)
+{
+        return t->immutable_target_type;
+}
+
 bool dm_table_request_based(struct dm_table *t)
 {
         return dm_table_get_type(t) == DM_TYPE_REQUEST_BASED;