Linux Virtualization - Apr 2015 - [PATCH v5 6/8] virtio: add explicit big-endian support to memory accessors

On Thu, 23 Apr 2015 17:29:06 +0200
Greg Kurz <gkurz at linux.vnet.ibm.com> wrote:
> The current memory accessors logic is:
> - little endian if little_endian
> - native endian (i.e. no byteswap) if !little_endian
> 
> If we want to fully support cross-endian vhost, we also need to be
> able to convert to big endian.
> 
> Instead of changing the little_endian argument to some 3-value enum, this
> patch changes the logic to:
> - little endian if little_endian
> - big endian if !little_endian
> 
> The native endian case is handled by all users with a trivial helper. This
> patch doesn't change any functionality, nor it does add overhead.
> 
> Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> ---
> 
> Changes since v4:
> - style fixes (I have chosen if ... else in most places to stay below
>   80 columns, with the notable exception of the vhost helper which gets
>   shorten in a later patch)
> 
>  drivers/net/macvtap.c            |    5 ++++-
>  drivers/net/tun.c                |    5 ++++-
>  drivers/vhost/vhost.h            |    2 +-
>  include/linux/virtio_byteorder.h |   24 ++++++++++++++----------
>  include/linux/virtio_config.h    |    5 ++++-
>  include/linux/vringh.h           |    2 +-
>  6 files changed, 28 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index a2f2958..6cf6b3e 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -51,7 +51,10 @@ struct macvtap_queue {
>  
>  static inline bool macvtap_is_little_endian(struct macvtap_queue *q)
>  {
> -	return q->flags & MACVTAP_VNET_LE;
> +	if (q->flags & MACVTAP_VNET_LE)
> +		return true;
> +	else
> +		return virtio_legacy_is_little_endian();
simply:

	return (q->flags & MACVTAP_VNET_LE) ||
	       virtio_legacy_is_little_endian();

?
>  }
>  
>  static inline u16 macvtap16_to_cpu(struct macvtap_queue *q, __virtio16
val)
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 3c3d6c0..5b044d4 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -208,7 +208,10 @@ struct tun_struct {
>  
>  static inline bool tun_is_little_endian(struct tun_struct *tun)
>  {
> -	return tun->flags & TUN_VNET_LE;
> +	if (tun->flags & TUN_VNET_LE)
> +		return true;
> +	else
> +		return virtio_legacy_is_little_endian();
dito?
>  }
>  
>  static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 6a49960..954c657 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -175,7 +175,7 @@ static inline bool vhost_has_feature(struct
vhost_virtqueue *vq, int bit)
>  
>  static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
>  {
> -	return vhost_has_feature(vq, VIRTIO_F_VERSION_1);
> +	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ? true :
virtio_legacy_is_little_endian();
>  }
That line is way longer than 80 characters ... may I suggest to switch
at least here to:

	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
	       virtio_legacy_is_little_endian();

?

Apart from the cosmetics, the patch looks good to me.

 Thomas

On Thu, 23 Apr 2015 21:27:19 +0200
Thomas Huth <thuth at redhat.com> wrote:
> On Thu, 23 Apr 2015 17:29:06 +0200
> Greg Kurz <gkurz at linux.vnet.ibm.com> wrote:
> 
> > The current memory accessors logic is:
> > - little endian if little_endian
> > - native endian (i.e. no byteswap) if !little_endian
> > 
> > If we want to fully support cross-endian vhost, we also need to be
> > able to convert to big endian.
> > 
> > Instead of changing the little_endian argument to some 3-value enum,
this
> > patch changes the logic to:
> > - little endian if little_endian
> > - big endian if !little_endian
> > 
> > The native endian case is handled by all users with a trivial helper.
This
> > patch doesn't change any functionality, nor it does add overhead.
> > 
> > Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> > ---
> > 
> > Changes since v4:
> > - style fixes (I have chosen if ... else in most places to stay below
> >   80 columns, with the notable exception of the vhost helper which
gets
> >   shorten in a later patch)
> > 
> >  drivers/net/macvtap.c            |    5 ++++-
> >  drivers/net/tun.c                |    5 ++++-
> >  drivers/vhost/vhost.h            |    2 +-
> >  include/linux/virtio_byteorder.h |   24 ++++++++++++++----------
> >  include/linux/virtio_config.h    |    5 ++++-
> >  include/linux/vringh.h           |    2 +-
> >  6 files changed, 28 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> > index a2f2958..6cf6b3e 100644
> > --- a/drivers/net/macvtap.c
> > +++ b/drivers/net/macvtap.c
> > @@ -51,7 +51,10 @@ struct macvtap_queue {
> >  
> >  static inline bool macvtap_is_little_endian(struct macvtap_queue *q)
> >  {
> > -	return q->flags & MACVTAP_VNET_LE;
> > +	if (q->flags & MACVTAP_VNET_LE)
> > +		return true;
> > +	else
> > +		return virtio_legacy_is_little_endian();
> 
> simply:
> 
> 	return (q->flags & MACVTAP_VNET_LE) ||
> 	       virtio_legacy_is_little_endian();
> 
> ?
ISTR that MST preferred the current notation, but I like either your
way or ?: (with linebreak) even better.
> 
> >  }
> >  
(...)
> > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > index 6a49960..954c657 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -175,7 +175,7 @@ static inline bool vhost_has_feature(struct
vhost_virtqueue *vq, int bit)
> >  
> >  static inline bool vhost_is_little_endian(struct vhost_virtqueue *vq)
> >  {
> > -	return vhost_has_feature(vq, VIRTIO_F_VERSION_1);
> > +	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ? true :
virtio_legacy_is_little_endian();
> >  }
> 
> That line is way longer than 80 characters ... may I suggest to switch
> at least here to:
> 
> 	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
> 	       virtio_legacy_is_little_endian();
I think the line will collapse in a further patch anyway.

On Fri, 24 Apr 2015 09:04:21 +0200
Cornelia Huck <cornelia.huck at de.ibm.com> wrote:
> On Thu, 23 Apr 2015 21:27:19 +0200
> Thomas Huth <thuth at redhat.com> wrote:
> 
Thomas's e-mail did not make it to my mailbox... weird. :-\
> > On Thu, 23 Apr 2015 17:29:06 +0200
> > Greg Kurz <gkurz at linux.vnet.ibm.com> wrote:
> > 
> > > The current memory accessors logic is:
> > > - little endian if little_endian
> > > - native endian (i.e. no byteswap) if !little_endian
> > > 
> > > If we want to fully support cross-endian vhost, we also need to
be
> > > able to convert to big endian.
> > > 
> > > Instead of changing the little_endian argument to some 3-value
enum, this
> > > patch changes the logic to:
> > > - little endian if little_endian
> > > - big endian if !little_endian
> > > 
> > > The native endian case is handled by all users with a trivial
helper. This
> > > patch doesn't change any functionality, nor it does add
overhead.
> > > 
> > > Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
> > > ---
> > > 
> > > Changes since v4:
> > > - style fixes (I have chosen if ... else in most places to stay
below
> > >   80 columns, with the notable exception of the vhost helper
which gets
> > >   shorten in a later patch)
> > > 
> > >  drivers/net/macvtap.c            |    5 ++++-
> > >  drivers/net/tun.c                |    5 ++++-
> > >  drivers/vhost/vhost.h            |    2 +-
> > >  include/linux/virtio_byteorder.h |   24 ++++++++++++++----------
> > >  include/linux/virtio_config.h    |    5 ++++-
> > >  include/linux/vringh.h           |    2 +-
> > >  6 files changed, 28 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> > > index a2f2958..6cf6b3e 100644
> > > --- a/drivers/net/macvtap.c
> > > +++ b/drivers/net/macvtap.c
> > > @@ -51,7 +51,10 @@ struct macvtap_queue {
> > >  
> > >  static inline bool macvtap_is_little_endian(struct macvtap_queue
*q)
> > >  {
> > > -	return q->flags & MACVTAP_VNET_LE;
> > > +	if (q->flags & MACVTAP_VNET_LE)
> > > +		return true;
> > > +	else
> > > +		return virtio_legacy_is_little_endian();
> > 
> > simply:
> > 
> > 	return (q->flags & MACVTAP_VNET_LE) ||
> > 	       virtio_legacy_is_little_endian();
> > 
> > ?
> 
> ISTR that MST preferred the current notation, but I like either your
> way or ?: (with linebreak) even better.
> 
MST did not like the initial notation I had used actually. FWIW I
like the simplicity of Thomas's suggestion... even better than ?:
which is:
         some_LE_check() ? true : some_default_endianness()
> > 
> > >  }
> > >  
> (...)
> > > diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> > > index 6a49960..954c657 100644
> > > --- a/drivers/vhost/vhost.h
> > > +++ b/drivers/vhost/vhost.h
> > > @@ -175,7 +175,7 @@ static inline bool vhost_has_feature(struct
vhost_virtqueue *vq, int bit)
> > >  
> > >  static inline bool vhost_is_little_endian(struct vhost_virtqueue
*vq)
> > >  {
> > > -	return vhost_has_feature(vq, VIRTIO_F_VERSION_1);
> > > +	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ? true :
virtio_legacy_is_little_endian();
> > >  }
> > 
> > That line is way longer than 80 characters ... may I suggest to switch
> > at least here to:
> > 
> > 	return vhost_has_feature(vq, VIRTIO_F_VERSION_1) ||
> > 	       virtio_legacy_is_little_endian();
> 
> I think the line will collapse in a further patch anyway.
> 
Yes, as mentionned in the changelog :)
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