linux-kernel - Re: [PATCH v7 28/46] vhost: make features 64 bit

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Date:	Mon, 01 Dec 2014 04:12:37 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	cornelia.huck@...ibm.com, rusty@....ibm.com, nab@...ux-iscsi.org,
	pbonzini@...hat.com, thuth@...ux.vnet.ibm.com,
	dahi@...ux.vnet.ibm.com, Jason Wang <jasowang@...hat.com>,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v7 28/46] vhost: make features 64 bit

On Sun, 2014-11-30 at 18:44 +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 11/30/2014 6:11 PM, Michael S. Tsirkin wrote:
> 
> > We need to use bit 32 for virtio 1.0
> 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> > Reviewed-by: Jason Wang <jasowang@...hat.com>
> > ---
> >   drivers/vhost/vhost.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index 3eda654..c624b09 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -106,7 +106,7 @@ struct vhost_virtqueue {
> >   	/* Protected by virtqueue mutex. */
> >   	struct vhost_memory *memory;
> >   	void *private_data;
> > -	unsigned acked_features;
> > +	u64 acked_features;
> >   	/* Log write descriptors */
> >   	void __user *log_base;
> >   	struct vhost_log *log;
> > @@ -174,6 +174,6 @@ enum {
> >
> >   static inline int vhost_has_feature(struct vhost_virtqueue *vq, int bit)
> >   {
> > -	return vq->acked_features & (1 << bit);
> > +	return vq->acked_features & (1ULL << bit);
> 
>     Erm, wouldn't the high word be just dropped when returning *int*? I think 
> you need !!(vq->acked_features & (1ULL << bit)).

Or change the return type to bool.

Ben.

-- 
Ben Hutchings
The first rule of tautology club is the first rule of tautology club.

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