Re: [Qemu-devel] [PATCH v3 13/21] scsi: do not call send_command directly

[Christoph Hellwig]

> -void scsi_req_enqueue(SCSIRequest *req)
> +int32_t scsi_req_enqueue(SCSIRequest *req, uint8_t *buf)
>  {
> +    int32_t rc;
>      assert(!req->enqueued);
>      scsi_req_ref(req);
>      req->enqueued = true;
>      QTAILQ_INSERT_TAIL(&req->dev->requests, req, next);
> +
> +    /* Make sure the request doesn't disappear under send_command's feet.  */
> +    scsi_req_ref(req);
> +    rc = req->dev->info->send_command(req, buf);
> +    scsi_req_unref(req);
> +    return rc;

How would it disappear given that we grabbed another reference just before?
That probably needs a bit more documentation here.  Also why not move
the two scsi_req_ref calls together?