linux-kernel - Re: [PATCH 1/2] vhost: helpers to enable/disable vring endianness

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Date:	Wed, 10 Feb 2016 14:12:55 +0100
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Greg Kurz <gkurz@...ux.vnet.ibm.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 1/2] vhost: helpers to enable/disable vring endianness

On Wed, 10 Feb 2016 13:11:34 +0100
Greg Kurz <gkurz@...ux.vnet.ibm.com> wrote:

> On Wed, 10 Feb 2016 13:21:22 +0200
> "Michael S. Tsirkin" <mst@...hat.com> wrote:
> 
> > On Wed, Jan 13, 2016 at 06:09:41PM +0100, Greg Kurz wrote:

> > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > index ad2146a9ab2d..e02e06755ab7 100644
> > > --- a/drivers/vhost/vhost.c
> > > +++ b/drivers/vhost/vhost.c
> > > @@ -43,11 +43,16 @@ enum {
> > >  #define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num])
> > >  
> > >  #ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
> > > -static void vhost_vq_reset_user_be(struct vhost_virtqueue *vq)
> > > +static void vhost_disable_user_be(struct vhost_virtqueue *vq)
> > >  {
> > >  	vq->user_be = !virtio_legacy_is_little_endian();
> > >  }
> > >    
> > 
> > Hmm this doesn't look like an improvement to me.
> > What does it mean to disable big endian? Make it little endian?
> 
> The default behavior for the device is native endian.
> 
> The SET_VRING_ENDIAN ioctl is used to make the device big endian
> on little endian hosts, hence "enabling" cross-endian mode...
> 
> > Existing reset seems to make sense.
> > 
> 
> ... and we "disable" cross-endian mode on reset.
> 
> > > +static void vhost_enable_user_be(struct vhost_virtqueue *vq, bool user_be)
> > > +{
> > > +	vq->user_be = user_be;
> > > +}
> > > +  
> > 
> > And this is maybe "init_user_be"?
> > 
> 
> Anyway I don't mind changing the names to reset/init_user_be if you think it
> is clearer.

FWIW, I find the enable/disable terminology less confusing.