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

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Message-ID: <20251119073155-mutt-send-email-mst@kernel.org>
Date: Wed, 19 Nov 2025 07:34:57 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: linux-kernel@...r.kernel.org, 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 Wed, Nov 19, 2025 at 12:04:12PM +0100, Paolo Abeni wrote:
> 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];


Ah. Good point.


> 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`,

This one I don't want to do, people tend to copy/paste code
and this is not what devices should be doing.

> the following two chunks
> should not be needed.
> 
> Thanks,
> 
> Paolo