It is not possible to instantiate a virtio-blk device with 0 virtqueues. The following check is located in ->realize(): if (!conf->num_queues) { error_setg(errp, "num-queues property must be larger than 0"); return; } Later on we access s->vq_aio_context[0] under the assumption that there is as least one virtqueue. Hanna Czenczek <hreitz@redhat.com> noted that it would help to show that the array index is already valid. Add an assertion to document that s->vq_aio_context[0] is always safe...and catch future code changes that break this assumption. Suggested-by: Hanna Czenczek <hreitz@redhat.com> Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org> Reviewed-by: Hanna Czenczek <hreitz@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-ID: <20240206190610.107963-3-stefanha@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>