linux-kernel - Re: [RFC 1/3] vdpa: support exposing the config size to userspace

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Message-ID: <ce3890b8-8f48-847d-b029-e29cc9261f18@redhat.com>
Date:   Tue, 18 Jan 2022 11:06:42 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Longpeng(Mike)" <longpeng2@...wei.com>, mst@...hat.com,
        sgarzare@...hat.com, stefanha@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        arei.gonglei@...wei.com, yechuan@...wei.com,
        huangzhichao@...wei.com
Subject: Re: [RFC 1/3] vdpa: support exposing the config size to userspace


在 2022/1/17 下午5:29, Longpeng(Mike) 写道:
> From: Longpeng <longpeng2@...wei.com>
>
> - GET_CONFIG_SIZE: the size of the virtio config space


I think we need to be verbose here. And it would be better to quote what 
spec said:

"

The device MUST allow reading of any device-specific configuration field 
before FEATURES_OK is set by the driver. This includes fields which are 
conditional on feature bits, as long as those feature bits are offered 
by the device.

"

I guess the size should contain the conditional on features bits.

(Or maybe we need to tweak the comment for get_config_size as well).

Other looks good.

Thanks


>
> Signed-off-by: Longpeng <longpeng2@...wei.com>
> ---
>   drivers/vhost/vdpa.c       | 17 +++++++++++++++++
>   include/uapi/linux/vhost.h |  4 ++++
>   2 files changed, 21 insertions(+)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 29cced1cd277..1eea14a4ea56 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -355,6 +355,20 @@ static long vhost_vdpa_get_iova_range(struct vhost_vdpa *v, u32 __user *argp)
>   	return 0;
>   }
>   
> +static long vhost_vdpa_get_config_size(struct vhost_vdpa *v, u32 __user *argp)
> +{
> +	struct vdpa_device *vdpa = v->vdpa;
> +	const struct vdpa_config_ops *ops = vdpa->config;
> +	u32 size;
> +
> +	size = ops->get_config_size(vdpa);
> +
> +	if (copy_to_user(argp, &size, sizeof(size)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
>   static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>   				   void __user *argp)
>   {
> @@ -492,6 +506,9 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>   	case VHOST_VDPA_GET_IOVA_RANGE:
>   		r = vhost_vdpa_get_iova_range(v, argp);
>   		break;
> +	case VHOST_VDPA_GET_CONFIG_SIZE:
> +		r = vhost_vdpa_get_config_size(v, argp);
> +		break;
>   	default:
>   		r = vhost_dev_ioctl(&v->vdev, cmd, argp);
>   		if (r == -ENOIOCTLCMD)
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index c998860d7bbc..bc74e95a273a 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -150,4 +150,8 @@
>   /* Get the valid iova range */
>   #define VHOST_VDPA_GET_IOVA_RANGE	_IOR(VHOST_VIRTIO, 0x78, \
>   					     struct vhost_vdpa_iova_range)
> +
> +/* Get the config size */
> +#define VHOST_VDPA_GET_CONFIG_SIZE	_IOR(VHOST_VIRTIO, 0x79, __u32)
> +
>   #endif