linux-kernel - Re: [PATCH v5 2/2] vhost: switch to arrays of feature bits

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Message-ID: <4204ed4b-0da1-407f-84e0-e23e2ce65fc7@redhat.com>
Date: Wed, 19 Nov 2025 12:04:12 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc: Andrew Lunn <andrew@...n.ch>, Jason Wang <jasowang@...hat.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Jonathan Corbet <corbet@....net>,
 kvm@...r.kernel.org, virtualization@...ts.linux.dev, netdev@...r.kernel.org,
 linux-doc@...r.kernel.org, Mike Christie <michael.christie@...cle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 Stefano Garzarella <sgarzare@...hat.com>
Subject: Re: [PATCH v5 2/2] vhost: switch to arrays of feature bits

On 11/19/25 7:55 AM, Michael S. Tsirkin wrote:
> @@ -1720,6 +1720,7 @@ static long vhost_net_set_owner(struct vhost_net *n)
>  static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
>  			    unsigned long arg)
>  {
> +	const DEFINE_VHOST_FEATURES_ARRAY(features_array, vhost_net_features);

I'm sorry for the late feedback, I was drowning in other stuff.

I have just a couple of non blocking suggestions, feel free to ignore.

I think that if you rename `vhost_net_features` as
`vhost_net_features_bits` and `features_array` as `vhost_net_features`
the diffstat could be smaller and possibly clearer.

>  	u64 all_features[VIRTIO_FEATURES_U64S];
>  	struct vhost_net *n = f->private_data;
>  	void __user *argp = (void __user *)arg;
> @@ -1734,14 +1735,14 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
>  			return -EFAULT;
>  		return vhost_net_set_backend(n, backend.index, backend.fd);
>  	case VHOST_GET_FEATURES:
> -		features = vhost_net_features[0];
> +		features = VHOST_FEATURES_U64(vhost_net_features, 0);

Here and below you could use directly:

		features = features_array[0];

if you apply the rename mentioned above, this chunk and the following 3
should not be needed.

[...]> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
> index 42c955a5b211..af727fccfe40 100644
> --- a/drivers/vhost/test.c
> +++ b/drivers/vhost/test.c
> @@ -308,6 +308,12 @@ static long vhost_test_set_backend(struct vhost_test *n, unsigned index, int fd)
>  	return r;
>  }
>  
> +static const int vhost_test_features[] = {
> +	VHOST_FEATURES
> +};
> +
> +#define VHOST_TEST_FEATURES VHOST_FEATURES_U64(vhost_test_features, 0)

If you rename `VHOST_FEATURES` to `VHOST_FEATURES_BITS` and
`VHOST_TEST_FEATURES` to `VHOST_FEATURES`, the following two chunks
should not be needed.

Thanks,

Paolo