block: Attach non-qdev devices as well

For now, this just protects against programming errors like having the
same drive back multiple non-qdev devices, or untimely bdrv_delete().
Later commits will add other interesting uses.

While there, rename BlockDriverState member peer to dev, bdrv_attach()
to bdrv_attach_dev(), bdrv_detach() to bdrv_detach_dev(), and
bdrv_get_attached() to bdrv_get_attached_dev().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block_int.h b/block_int.h
index 8a72b80..adc26f8 100644
--- a/block_int.h
+++ b/block_int.h
@@ -168,7 +168,8 @@
     BlockDriver *drv; /* NULL means no media */
     void *opaque;
 
-    DeviceState *peer;
+    void *dev;                  /* attached device model, if any */
+    /* TODO change to DeviceState when all users are qdevified */
 
     char filename[1024];
     char backing_file[1024]; /* if non zero, the image is a diff of