block: Add BB-BDS remove/insert notifiers

bdrv_close() no longer signifies ejection of a medium, this is now done
by removing the BDS from the BB. Therefore, we want to have a notifier
for that in the BB instead of a close notifier in the BDS. The former is
added now, the latter is removed later.

Symmetrically, another notifier list is added that is invoked whenever a
BDS is inserted. We will need that for virtio-blk and virtio-scsi, which
can then remove their op blockers on BDS ejection and set them up on
insertion.

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

block/block-backend.c

@@ -49,6 +49,8 @@ struct BlockBackend {
     BlockdevOnError on_read_error, on_write_error;
     bool iostatus_enabled;
     BlockDeviceIoStatus iostatus;
+
+    NotifierList remove_bs_notifiers, insert_bs_notifiers;
 };
 
 typedef struct BlockBackendAIOCB {
@@ -99,6 +101,8 @@ BlockBackend *blk_new(const char *name, Error **errp)
     blk = g_new0(BlockBackend, 1);
     blk->name = g_strdup(name);
     blk->refcnt = 1;
+    notifier_list_init(&blk->remove_bs_notifiers);
+    notifier_list_init(&blk->insert_bs_notifiers);
     QTAILQ_INSERT_TAIL(&blk_backends, blk, link);
     return blk;
 }
@@ -167,6 +171,8 @@ static void blk_delete(BlockBackend *blk)
         bdrv_unref(blk->bs);
         blk->bs = NULL;
     }
+    assert(QLIST_EMPTY(&blk->remove_bs_notifiers.notifiers));
+    assert(QLIST_EMPTY(&blk->insert_bs_notifiers.notifiers));
     if (blk->root_state.throttle_state) {
         g_free(blk->root_state.throttle_group);
         throttle_group_unref(blk->root_state.throttle_state);
@@ -345,6 +351,8 @@ void blk_hide_on_behalf_of_hmp_drive_del(BlockBackend *blk)
  */
 void blk_remove_bs(BlockBackend *blk)
 {
+    notifier_list_notify(&blk->remove_bs_notifiers, blk);
+
     blk_update_root_state(blk);
 
     blk->bs->blk = NULL;
@@ -361,6 +369,8 @@ void blk_insert_bs(BlockBackend *blk, BlockDriverState *bs)
     bdrv_ref(bs);
     blk->bs = bs;
     bs->blk = blk;
+
+    notifier_list_notify(&blk->insert_bs_notifiers, blk);
 }
 
 /*
@@ -1126,6 +1136,16 @@ void blk_remove_aio_context_notifier(BlockBackend *blk,
     }
 }
 
+void blk_add_remove_bs_notifier(BlockBackend *blk, Notifier *notify)
+{
+    notifier_list_add(&blk->remove_bs_notifiers, notify);
+}
+
+void blk_add_insert_bs_notifier(BlockBackend *blk, Notifier *notify)
+{
+    notifier_list_add(&blk->insert_bs_notifiers, notify);
+}
+
 void blk_add_close_notifier(BlockBackend *blk, Notifier *notify)
 {
     if (blk->bs) {

include/sysemu/block-backend.h

@@ -164,6 +164,8 @@ void blk_remove_aio_context_notifier(BlockBackend *blk,
                                                                   void *),
                                      void (*detach_aio_context)(void *),
                                      void *opaque);
+void blk_add_remove_bs_notifier(BlockBackend *blk, Notifier *notify);
+void blk_add_insert_bs_notifier(BlockBackend *blk, Notifier *notify);
 void blk_add_close_notifier(BlockBackend *blk, Notifier *notify);
 void blk_io_plug(BlockBackend *blk);
 void blk_io_unplug(BlockBackend *blk);