block: Remove BlockDriverState.blk

This patch removes the remaining users of bs->blk, which will allow us
to have multiple BBs on top of a single BDS. In the meantime, all checks
that are currently in place to prevent the user from creating such
setups can be switched to bdrv_has_blk() instead of accessing BDS.blk.

Future patches can allow them and e.g. enable users to mirror to a block
device that already has a BlockBackend on it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

block.c

@@ -2226,14 +2226,6 @@ static void change_parent_backing_link(BlockDriverState *from,
 {
     BdrvChild *c, *next;
 
-    if (from->blk) {
-        /* FIXME We bypass blk_set_bs(), so we need to make these updates
-         * manually. The root problem is not in this change function, but the
-         * existence of BlockDriverState.blk. */
-        to->blk = from->blk;
-        from->blk = NULL;
-    }
-
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
         assert(c->role != &child_backing);
         c->bs = to;
@@ -2875,7 +2867,7 @@ const char *bdrv_get_node_name(const BlockDriverState *bs)
     return bs->node_name;
 }
 
-static const char *bdrv_get_parent_name(const BlockDriverState *bs)
+const char *bdrv_get_parent_name(const BlockDriverState *bs)
 {
     BdrvChild *c;
     const char *name;

block/block-backend.c

@@ -152,7 +152,6 @@ BlockBackend *blk_new_with_bs(Error **errp)
     bs = bdrv_new_root();
     blk->root = bdrv_root_attach_child(bs, "root", &child_root);
     blk->root->opaque = blk;
-    bs->blk = blk;
     return blk;
 }
 
@@ -422,12 +421,10 @@ static BlockBackend *bdrv_first_blk(BlockDriverState *bs)
     BdrvChild *child;
     QLIST_FOREACH(child, &bs->parents, next_parent) {
         if (child->role == &child_root) {
-            assert(bs->blk);
             return child->opaque;
         }
     }
 
-    assert(!bs->blk);
     return NULL;
 }
 
@@ -495,8 +492,6 @@ BlockBackend *blk_by_public(BlockBackendPublic *public)
  */
 void blk_remove_bs(BlockBackend *blk)
 {
-    assert(blk->root->bs->blk == blk);
-
     notifier_list_notify(&blk->remove_bs_notifiers, blk);
     if (blk->public.throttle_state) {
         throttle_timers_detach_aio_context(&blk->public.throttle_timers);
@@ -504,7 +499,6 @@ void blk_remove_bs(BlockBackend *blk)
 
     blk_update_root_state(blk);
 
-    blk->root->bs->blk = NULL;
     bdrv_root_unref_child(blk->root);
     blk->root = NULL;
 }
@@ -514,11 +508,9 @@ void blk_remove_bs(BlockBackend *blk)
  */
 void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs)
 {
-    assert(!blk->root && !bs->blk);
     bdrv_ref(bs);
     blk->root = bdrv_root_attach_child(bs, "root", &child_root);
     blk->root->opaque = blk;
-    bs->blk = blk;
 
     notifier_list_notify(&blk->insert_bs_notifiers, blk);
     if (blk->public.throttle_state) {

block/mirror.c

@@ -468,7 +468,7 @@ static void mirror_exit(BlockJob *job, void *opaque)
 
         /* This was checked in mirror_start_job(), but meanwhile one of the
          * nodes could have been newly attached to a BlockBackend. */
-        if (to_replace->blk && s->target->blk) {
+        if (bdrv_has_blk(to_replace) && bdrv_has_blk(s->target)) {
             error_report("block job: Can't create node with two BlockBackends");
             data->ret = -EINVAL;
             goto out;
@@ -831,7 +831,7 @@ static void mirror_start_job(BlockDriverState *bs, BlockDriverState *target,
     } else {
         replaced_bs = bs;
     }
-    if (replaced_bs->blk && target->blk) {
+    if (bdrv_has_blk(replaced_bs) && bdrv_has_blk(target)) {
         error_setg(errp, "Can't create node with two BlockBackends");
         return;
     }

blockdev.c

@@ -1776,9 +1776,9 @@ static void external_snapshot_prepare(BlkActionState *common,
         return;
     }
 
-    if (state->new_bs->blk != NULL) {
+    if (bdrv_has_blk(state->new_bs)) {
         error_setg(errp, "The snapshot is already in use by %s",
-                   blk_name(state->new_bs->blk));
+                   bdrv_get_parent_name(state->new_bs));
         return;
     }
 
@@ -2494,9 +2494,9 @@ void qmp_x_blockdev_insert_medium(const char *device, const char *node_name,
         return;
     }
 
-    if (bs->blk) {
+    if (bdrv_has_blk(bs)) {
         error_setg(errp, "Node '%s' is already in use by '%s'", node_name,
-                   blk_name(bs->blk));
+                   bdrv_get_parent_name(bs));
         return;
     }
 
@@ -3441,7 +3441,7 @@ static void blockdev_mirror_common(BlockDriverState *bs,
     if (bdrv_op_is_blocked(target, BLOCK_OP_TYPE_MIRROR_TARGET, errp)) {
         return;
     }
-    if (target->blk) {
+    if (bdrv_has_blk(target)) {
         error_setg(errp, "Cannot mirror to an attached block device");
         return;
     }
@@ -4030,15 +4030,15 @@ void qmp_x_blockdev_del(bool has_id, const char *id,
         bs = blk_bs(blk);
         aio_context = blk_get_aio_context(blk);
     } else {
+        blk = NULL;
         bs = bdrv_find_node(node_name);
         if (!bs) {
             error_setg(errp, "Cannot find node %s", node_name);
             return;
         }
-        blk = bs->blk;
+        if (bdrv_has_blk(bs)) {
-        if (blk) {
             error_setg(errp, "Node %s is in use by %s",
-                       node_name, blk_name(blk));
+                       node_name, bdrv_get_parent_name(bs));
             return;
         }
         aio_context = bdrv_get_aio_context(bs);

include/block/block_int.h

@@ -418,8 +418,6 @@ struct BlockDriverState {
     BlockDriver *drv; /* NULL means no media */
     void *opaque;
 
-    BlockBackend *blk;          /* owning backend, if any */
-
     AioContext *aio_context; /* event loop used for fd handlers, timers, etc */
     /* long-running tasks intended to always use the same AioContext as this
      * BDS may register themselves in this list to be notified of changes
@@ -724,6 +722,7 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
                                   const BdrvChildRole *child_role);
 void bdrv_root_unref_child(BdrvChild *child);
 
+const char *bdrv_get_parent_name(const BlockDriverState *bs);
 void blk_dev_change_media_cb(BlockBackend *blk, bool load);
 bool blk_dev_has_removable_media(BlockBackend *blk);
 bool blk_dev_has_tray(BlockBackend *blk);