linux-kernel - Re: [virtio-dev] [PATCH 2/2] virtio: document virtio_config

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Message-ID: <5C3D42E1.7030005@intel.com>
Date:   Tue, 15 Jan 2019 10:18:09 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>
CC:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, virtio-dev@...ts.oasis-open.org,
        Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [virtio-dev] [PATCH 2/2] virtio: document virtio_config_ops restrictions

On 01/04/2019 12:08 AM, Cornelia Huck wrote:
> Some transports (e.g. virtio-ccw) implement virtio operations that
> seem to be a simple read/write as something more involved that
> cannot be done from an atomic context.
>
> Give at least a hint about that.
>
> Signed-off-by: Cornelia Huck <cohuck@...hat.com>
> ---
>   include/linux/virtio_config.h | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 7087ef946ba7..987b6491b946 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -12,6 +12,11 @@ struct irq_affinity;
>   
>   /**
>    * virtio_config_ops - operations for configuring a virtio device
> + * Note: Do not assume that a transport implements all of the operations
> + *       getting/setting a value as a simple read/write! Generally speaking,
> + *       any of @get/@set, @get_status/@..._status, or @get_features/
> + *       @finalize_features are NOT safe to be called from an atomic
> + *       context.
>    * @get: read the value of a configuration field
>    *	vdev: the virtio_device
>    *	offset: the offset of the configuration field


Reviewed-by: Wei Wang <wei.w.wang@...el.com>

Best,
Wei