dm ioctl: make bio or request based device type immutable

Determine whether a mapped device is bio-based or request-based when
loading its first (inactive) table and don't allow that to be changed
later.

This patch performs different device initialisation in each of the two
cases.  (We don't think it's necessary to add code to support changing
between the two types.)

Allowed md->type transitions:
  DM_TYPE_NONE to DM_TYPE_BIO_BASED
  DM_TYPE_NONE to DM_TYPE_REQUEST_BASED

We now prevent table_load from replacing the inactive table with a
conflicting type of table even after an explicit table_clear.

Introduce 'type_lock' into the struct mapped_device to protect md->type
and to prepare for the next patch that will change the queue
initialization and allocate memory while md->type_lock is held.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Acked-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

 drivers/md/dm-ioctl.c    |   15 +++++++++++++++
 drivers/md/dm.c          |   37 ++++++++++++++++++++++++++++++-------
 drivers/md/dm.h          |    5 +++++
 include/linux/dm-ioctl.h |    4 ++--
 4 files changed, 52 insertions(+), 9 deletions(-)

1 files changed, 30 insertions, 7 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f3cc5d99fe8d..345e94c10c65 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -125,6 +125,10 @@ struct mapped_device {
         unsigned long flags;
 
         struct request_queue *queue;
+        unsigned type;
+        /* Protect type against concurrent access. */
+        struct mutex type_lock;
+
         struct gendisk *disk;
         char name[16];
 
@@ -1877,8 +1881,10 @@ static struct mapped_device *alloc_dev(int minor)
         if (r < 0)
                 goto bad_minor;
 
+        md->type = DM_TYPE_NONE;
         init_rwsem(&md->io_lock);
         mutex_init(&md->suspend_lock);
+        mutex_init(&md->type_lock);
         spin_lock_init(&md->deferred_lock);
         spin_lock_init(&md->barrier_error_lock);
         rwlock_init(&md->map_lock);
@@ -2130,6 +2136,30 @@ int dm_create(int minor, struct mapped_device **result)
         return 0;
 }
 
+/*
+ * Functions to manage md->type.
+ * All are required to hold md->type_lock.
+ */
+void dm_lock_md_type(struct mapped_device *md)
+{
+        mutex_lock(&md->type_lock);
+}
+
+void dm_unlock_md_type(struct mapped_device *md)
+{
+        mutex_unlock(&md->type_lock);
+}
+
+void dm_set_md_type(struct mapped_device *md, unsigned type)
+{
+        md->type = type;
+}
+
+unsigned dm_get_md_type(struct mapped_device *md)
+{
+        return md->type;
+}
+
 static struct mapped_device *dm_find_md(dev_t dev)
 {
         struct mapped_device *md;
@@ -2440,13 +2470,6 @@ struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
                 goto out;
         }
 
-        /* cannot change the device type, once a table is bound */
-        if (md->map &&
-            (dm_table_get_type(md->map) != dm_table_get_type(table))) {
-                DMWARN("can't change the device type after a table is bound");
-                goto out;
-        }
-
         map = __bind(md, table, &limits);
 
 out: