linux-kernel - Re: [RFC PATCH 10/10] vhost/vdpa: return configuration bytes read and written to user space

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Date:   Tue, 2 Mar 2021 12:05:35 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Stefano Garzarella <sgarzare@...hat.com>,
        virtualization@...ts.linux-foundation.org
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [RFC PATCH 10/10] vhost/vdpa: return configuration bytes read and
 written to user space


On 2021/2/16 5:44 下午, Stefano Garzarella wrote:
> vdpa_get_config() and vdpa_set_config() now return the amount
> of bytes read and written, so let's return them to the user space.
>
> We also modify vhost_vdpa_config_validate() to return 0 (bytes read
> or written) instead of an error, when the buffer length is 0.
>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
>   drivers/vhost/vdpa.c | 26 +++++++++++++++-----------
>   1 file changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 21eea2be5afa..b754c53171a7 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -191,9 +191,6 @@ static ssize_t vhost_vdpa_config_validate(struct vhost_vdpa *v,
>   	struct vdpa_device *vdpa = v->vdpa;
>   	u32 size = vdpa->config->get_config_size(vdpa);
>   
> -	if (c->len == 0)
> -		return -EINVAL;
> -
>   	return min(c->len, size);
>   }
>   
> @@ -204,6 +201,7 @@ static long vhost_vdpa_get_config(struct vhost_vdpa *v,
>   	struct vhost_vdpa_config config;
>   	unsigned long size = offsetof(struct vhost_vdpa_config, buf);
>   	ssize_t config_size;
> +	long ret;
>   	u8 *buf;
>   
>   	if (copy_from_user(&config, c, size))
> @@ -217,15 +215,18 @@ static long vhost_vdpa_get_config(struct vhost_vdpa *v,
>   	if (!buf)
>   		return -ENOMEM;
>   
> -	vdpa_get_config(vdpa, config.off, buf, config_size);
> -
> -	if (copy_to_user(c->buf, buf, config_size)) {
> -		kvfree(buf);
> -		return -EFAULT;
> +	ret = vdpa_get_config(vdpa, config.off, buf, config_size);
> +	if (ret < 0) {
> +		ret = -EFAULT;
> +		goto out;
>   	}
>   
> +	if (copy_to_user(c->buf, buf, config_size))
> +		ret = -EFAULT;
> +
> +out:
>   	kvfree(buf);
> -	return 0;
> +	return ret;
>   }
>   
>   static long vhost_vdpa_set_config(struct vhost_vdpa *v,
> @@ -235,6 +236,7 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
>   	struct vhost_vdpa_config config;
>   	unsigned long size = offsetof(struct vhost_vdpa_config, buf);
>   	ssize_t config_size;
> +	long ret;
>   	u8 *buf;
>   
>   	if (copy_from_user(&config, c, size))
> @@ -248,10 +250,12 @@ static long vhost_vdpa_set_config(struct vhost_vdpa *v,
>   	if (IS_ERR(buf))
>   		return PTR_ERR(buf);
>   
> -	vdpa_set_config(vdpa, config.off, buf, config_size);
> +	ret = vdpa_set_config(vdpa, config.off, buf, config_size);
> +	if (ret < 0)
> +		ret = -EFAULT;
>   
>   	kvfree(buf);
> -	return 0;
> +	return ret;
>   }


So I wonder whether it's worth to return the number of bytes since we 
can't propogate the result to driver or driver doesn't care about that.

Thanks


>   
>   static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)