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>

4 files changed, 43 insertions, 0 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 2e9a3ca..31c2dc2 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)
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9917141..8e91321 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;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2fe3017..9836324 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).
  */
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 6745dbd..b7dacd5 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -60,6 +60,7 @@ int dm_table_resume_targets(struct dm_table *t);
 int dm_table_any_congested(struct dm_table *t, int bdi_bits);
 int dm_table_any_busy_target(struct dm_table *t);
 unsigned dm_table_get_type(struct dm_table *t);
+struct target_type *dm_table_get_immutable_target_type(struct dm_table *t);
 bool dm_table_request_based(struct dm_table *t);
 bool dm_table_supports_discards(struct dm_table *t);
 int dm_table_alloc_md_mempools(struct dm_table *t);
@@ -72,6 +73,7 @@ void dm_lock_md_type(struct mapped_device *md);
 void dm_unlock_md_type(struct mapped_device *md);
 void dm_set_md_type(struct mapped_device *md, unsigned type);
 unsigned dm_get_md_type(struct mapped_device *md);
+struct target_type *dm_get_immutable_target_type(struct mapped_device *md);
 
 int dm_setup_md_queue(struct mapped_device *md);