I just saw commit 30dd65f307b647eef8156c4a33bd007823ef85cb, and noticed that a similar pattern in drive_backup_prepare() and blockdev_backup_prepare().
The calls to bdrv_try_set_aio_context() seems useless, because we already do that later in backup_job_create/brdv_attach. But I am not 100%& sure?
