Subject: Re: [PATCH v2 1/2] virtio: clean up features qword/dword terms

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 22 Oct 2025 01:38:39 -0400

On Wed, Oct 22, 2025 at 04:20:52AM +0200, Andrew Lunn wrote:
> > @@ -1752,7 +1752,7 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> >  
> >  		/* Copy the net features, up to the user-provided buffer size */
> >  		argp += sizeof(u64);
> > -		copied = min(count, VIRTIO_FEATURES_DWORDS);
> > +		copied = min(count, (u64)VIRTIO_FEATURES_ARRAY_SIZE);
> 
> Why is the cast needed? Why was 2 O.K, but (128 >> 6) needs a cast?

It's not - a leftover from one of the approaches I tried, thanks!

> > -#define VIRTIO_FEATURES_DWORDS	2
> > -#define VIRTIO_FEATURES_MAX	(VIRTIO_FEATURES_DWORDS * 64)
> > -#define VIRTIO_FEATURES_WORDS	(VIRTIO_FEATURES_DWORDS * 2)
> > +#define VIRTIO_FEATURES_BITS	(128)
> >  #define VIRTIO_BIT(b)		BIT_ULL((b) & 0x3f)
> > -#define VIRTIO_DWORD(b)		((b) >> 6)
> > +#define VIRTIO_U64(b)		((b) >> 6)
> > +
> > +#define VIRTIO_FEATURES_ARRAY_SIZE VIRTIO_U64(VIRTIO_FEATURES_BITS)
> 
> 	Andrew