linux-kernel - Re: [PATCH v2 12/17] vdpa_sim: add get_config callback in vdpasim_dev

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Date:   Mon, 30 Nov 2020 11:25:31 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        linux-kernel@...r.kernel.org, Laurent Vivier <lvivier@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        "Michael S. Tsirkin" <mst@...hat.com>, Eli Cohen <elic@...dia.com>
Subject: Re: [PATCH v2 12/17] vdpa_sim: add get_config callback in
 vdpasim_dev_attr


On 2020/11/26 下午10:49, Stefano Garzarella wrote:
> The get_config callback can be used by the device to fill the
> config structure.
> The callback will be invoked in vdpasim_get_config() before copying
> bytes into caller buffer.
>
> Move vDPA-net config updates from vdpasim_set_features() in the
> new vdpasim_net_get_config() callback.
>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>   drivers/vdpa/vdpa_sim/vdpa_sim.c | 33 +++++++++++++++++++-------------
>   1 file changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index c07ddf6af720..8b87ce0485b6 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -58,6 +58,8 @@ struct vdpasim_virtqueue {
>   #define VDPASIM_NET_FEATURES	(VDPASIM_FEATURES | \
>   				 (1ULL << VIRTIO_NET_F_MAC))
>   
> +struct vdpasim;
> +
>   struct vdpasim_dev_attr {
>   	u64 supported_features;
>   	size_t config_size;
> @@ -65,6 +67,7 @@ struct vdpasim_dev_attr {
>   	u32 id;
>   
>   	work_func_t work_fn;
> +	void (*get_config)(struct vdpasim *vdpasim, void *config);
>   };
>   
>   /* State of each vdpasim device */
> @@ -520,8 +523,6 @@ static u64 vdpasim_get_features(struct vdpa_device *vdpa)
>   static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
>   {
>   	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
> -	struct virtio_net_config *config =
> -		(struct virtio_net_config *)vdpasim->config;
>   
>   	/* DMA mapping must be done by driver */
>   	if (!(features & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
> @@ -529,15 +530,6 @@ static int vdpasim_set_features(struct vdpa_device *vdpa, u64 features)
>   
>   	vdpasim->features = features & vdpasim->dev_attr.supported_features;
>   
> -	/* We generally only know whether guest is using the legacy interface
> -	 * here, so generally that's the earliest we can set config fields.
> -	 * Note: We actually require VIRTIO_F_ACCESS_PLATFORM above which
> -	 * implies VIRTIO_F_VERSION_1, but let's not try to be clever here.
> -	 */
> -
> -	config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> -	config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
> -	memcpy(config->mac, macaddr_buf, ETH_ALEN);
>   
>   	return 0;
>   }
> @@ -593,8 +585,12 @@ static void vdpasim_get_config(struct vdpa_device *vdpa, unsigned int offset,
>   {
>   	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>   
> -	if (offset + len < vdpasim->dev_attr.config_size)
> -		memcpy(buf, vdpasim->config + offset, len);
> +	if (offset + len > vdpasim->dev_attr.config_size)
> +		return;
> +
> +	vdpasim->dev_attr.get_config(vdpasim, vdpasim->config);
> +
> +	memcpy(buf, vdpasim->config + offset, len);
>   }


I wonder how much value we can get from vdpasim->config consider we've 
already had get_config() method.

Is it possible to copy to the buffer directly here?

Thanks


>   
>   static void vdpasim_set_config(struct vdpa_device *vdpa, unsigned int offset,
> @@ -737,6 +733,16 @@ static const struct vdpa_config_ops vdpasim_batch_config_ops = {
>   	.free                   = vdpasim_free,
>   };
>   
> +static void vdpasim_net_get_config(struct vdpasim *vdpasim, void *config)
> +{
> +	struct virtio_net_config *net_config =
> +		(struct virtio_net_config *)config;
> +
> +	net_config->mtu = cpu_to_vdpasim16(vdpasim, 1500);
> +	net_config->status = cpu_to_vdpasim16(vdpasim, VIRTIO_NET_S_LINK_UP);
> +	memcpy(net_config->mac, macaddr_buf, ETH_ALEN);
> +}
> +
>   static int __init vdpasim_dev_init(void)
>   {
>   	struct vdpasim_dev_attr dev_attr = {};
> @@ -745,6 +751,7 @@ static int __init vdpasim_dev_init(void)
>   	dev_attr.supported_features = VDPASIM_NET_FEATURES;
>   	dev_attr.nvqs = VDPASIM_VQ_NUM;
>   	dev_attr.config_size = sizeof(struct virtio_net_config);
> +	dev_attr.get_config = vdpasim_net_get_config;
>   	dev_attr.work_fn = vdpasim_net_work;
>   
>   	vdpasim_dev = vdpasim_create(&dev_attr);