Re: [PATCH v2 3/4] virtio: rng: delay hwrng_register() till driver is ready

[Jason Cooper <jason@lakedaemon.net>]

On Mon, Jul 21, 2014 at 05:15:51PM +0530, Amit Shah wrote:
> Instead of calling hwrng_register() in the probe routing, call it in the
> scan routine.  This ensures that when hwrng_register() is successful,
> and it requests a few random bytes to seed the kernel's pool at init,
> we're ready to service that request.
> 
> This will also enable us to remove the workaround added previously to
> check whether probe was completed, and only then ask for data from the
> host.  The revert follows in the next commit.
> 
> There's a slight behaviour change here on unsuccessful hwrng_register().
> Previously, when hwrng_unregister() failed, the probe() routine would
> fail, and the vqs would be torn down, and driver would be marked not
> initialized.  Now, the vqs will remain initialized, driver would be
> marked initialized as well, but won't be available in the list of RNGs
> available to hwrng core.  To fix the failures, the procedure remains the
> same, i.e. unload and re-load the module, and hope things succeed the
> next time around.

I'm not too comfortable with this.  I'll try to take a closer look
tonight, but in the meantime...

> Signed-off-by: Amit Shah <amit.shah@redhat.com>
> ---
>  drivers/char/hw_random/virtio-rng.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> index a156284..d9927eb 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -35,6 +35,7 @@ struct virtrng_info {
>  	unsigned int data_avail;
>  	int index;
>  	bool busy;
> +	bool hwrng_register_done;
>  };
>  
>  static bool probe_done;
> @@ -136,15 +137,6 @@ static int probe_common(struct virtio_device *vdev)
>  		return err;
>  	}
>  
> -	err = hwrng_register(&vi->hwrng);
> -	if (err) {
> -		vdev->config->del_vqs(vdev);
> -		vi->vq = NULL;
> -		kfree(vi);
> -		ida_simple_remove(&rng_index_ida, index);
> -		return err;
> -	}
> -

This needs to stay.  register, and failure to do so, should occur in the
probe routine.

>  	probe_done = true;
>  	return 0;
>  }
> @@ -152,9 +144,11 @@ static int probe_common(struct virtio_device *vdev)
>  static void remove_common(struct virtio_device *vdev)
>  {
>  	struct virtrng_info *vi = vdev->priv;
> +
>  	vdev->config->reset(vdev);
>  	vi->busy = false;
> -	hwrng_unregister(&vi->hwrng);
> +	if (vi->hwrng_register_done)
> +		hwrng_unregister(&vi->hwrng);
>  	vdev->config->del_vqs(vdev);
>  	ida_simple_remove(&rng_index_ida, vi->index);
>  	kfree(vi);
> @@ -170,6 +164,16 @@ static void virtrng_remove(struct virtio_device *vdev)
>  	remove_common(vdev);
>  }
>  
> +static void virtrng_scan(struct virtio_device *vdev)
> +{
> +	struct virtrng_info *vi = vdev->priv;
> +	int err;
> +
> +	err = hwrng_register(&vi->hwrng);
> +	if (!err)
> +		vi->hwrng_register_done = true;

Instead, perhaps we should just feed the entropy pool from here?  We
would still need to prevent the core from doing so.  Perhaps back to the
flag idea?

thx,

Jason.

> +}
> +
>  #ifdef CONFIG_PM_SLEEP
>  static int virtrng_freeze(struct virtio_device *vdev)
>  {
> @@ -194,6 +198,7 @@ static struct virtio_driver virtio_rng_driver = {
>  	.id_table =	id_table,
>  	.probe =	virtrng_probe,
>  	.remove =	virtrng_remove,
> +	.scan =		virtrng_scan,
>  #ifdef CONFIG_PM_SLEEP
>  	.freeze =	virtrng_freeze,
>  	.restore =	virtrng_restore,
> -- 
> 1.9.3
>