Re: [PATCH v4 6/8] virtio: add explicit big-endian support to memory accessors

Greg Kurz
2015-04-21T16:23:25Z

On Tue, 21 Apr 2015 16:09:44 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Fri, Apr 10, 2015 at 12:16:20PM +0200, Greg Kurz 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@linux.vnet.ibm.com>
> > ---
>
> OK overall. Style comment:
>
> > drivers/net/macvtap.c | 4 +++-
> > drivers/net/tun.c | 4 +++-
> > drivers/vhost/vhost.h | 4 +++-
> > include/linux/virtio_byteorder.h | 24 ++++++++++++++----------
> > include/linux/virtio_config.h | 4 +++-
> > include/linux/vringh.h | 4 +++-
> > 6 files changed, 29 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> > index a2f2958..0a03a66 100644
> > --- a/drivers/net/macvtap.c
> > +++ b/drivers/net/macvtap.c
> > @@ -51,7 +51,9 @@ 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;
> > + return virtio_legacy_is_little_endian();
> > }
> >
>
> I'd prefer a bit more symmetry:
>
> + if (q->flags & MACVTAP_VNET_LE)
> + return true;
> + else
> + return virtio_legacy_is_little_endian();
>
> Or better just:
> return (q->flags & MACVTAP_VNET_LE) ? true : virtio_legacy_is_little_endian();
>
> might make line long, but your follow-up patch makes it short again,
> so that's ok.
>

Will do.

>
> > 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..053f9b6 100644
> > --- a/drivers/net/tun.c
> > +++ b/drivers/net/tun.c
> > @@ -208,7 +208,9 @@ 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;
> > + return virtio_legacy_is_little_endian();
> > }
> >
> > 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..4e9a186 100644
> > --- a/drivers/vhost/vhost.h
> > +++ b/drivers/vhost/vhost.h
> > @@ -175,7 +175,9 @@ 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);
> > + if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
> > + return true;
> > + return virtio_legacy_is_little_endian();
> > }
> >
> > /* Memory accessors */
> > diff --git a/include/linux/virtio_byteorder.h b/include/linux/virtio_byteorder.h
> > index 51865d0..ce63a2c 100644
> > --- a/include/linux/virtio_byteorder.h
> > +++ b/include/linux/virtio_byteorder.h
> > @@ -3,17 +3,21 @@
> > #include <linux/types.h>
> > #include <uapi/linux/virtio_types.h>
> >
> > -/*
> > - * Low-level memory accessors for handling virtio in modern little endian and in
> > - * compatibility native endian format.
> > - */
> > +static inline bool virtio_legacy_is_little_endian(void)
> > +{
> > +#ifdef __LITTLE_ENDIAN
> > + return true;
> > +#else
> > + return false;
> > +#endif
> > +}
> >
> > static inline u16 __virtio16_to_cpu(bool little_endian, __virtio16 val)
> > {
> > if (little_endian)
> > return le16_to_cpu((__force __le16)val);
> > else
> > - return (__force u16)val;
> > + return be16_to_cpu((__force __be16)val);
> > }
> >
> > static inline __virtio16 __cpu_to_virtio16(bool little_endian, u16 val)
> > @@ -21,7 +25,7 @@ static inline __virtio16 __cpu_to_virtio16(bool little_endian, u16 val)
> > if (little_endian)
> > return (__force __virtio16)cpu_to_le16(val);
> > else
> > - return (__force __virtio16)val;
> > + return (__force __virtio16)cpu_to_be16(val);
> > }
> >
> > static inline u32 __virtio32_to_cpu(bool little_endian, __virtio32 val)
> > @@ -29,7 +33,7 @@ static inline u32 __virtio32_to_cpu(bool little_endian, __virtio32 val)
> > if (little_endian)
> > return le32_to_cpu((__force __le32)val);
> > else
> > - return (__force u32)val;
> > + return be32_to_cpu((__force __be32)val);
> > }
> >
> > static inline __virtio32 __cpu_to_virtio32(bool little_endian, u32 val)
> > @@ -37,7 +41,7 @@ static inline __virtio32 __cpu_to_virtio32(bool little_endian, u32 val)
> > if (little_endian)
> > return (__force __virtio32)cpu_to_le32(val);
> > else
> > - return (__force __virtio32)val;
> > + return (__force __virtio32)cpu_to_be32(val);
> > }
> >
> > static inline u64 __virtio64_to_cpu(bool little_endian, __virtio64 val)
> > @@ -45,7 +49,7 @@ static inline u64 __virtio64_to_cpu(bool little_endian, __virtio64 val)
> > if (little_endian)
> > return le64_to_cpu((__force __le64)val);
> > else
> > - return (__force u64)val;
> > + return be64_to_cpu((__force __be64)val);
> > }
> >
> > static inline __virtio64 __cpu_to_virtio64(bool little_endian, u64 val)
> > @@ -53,7 +57,7 @@ static inline __virtio64 __cpu_to_virtio64(bool little_endian, u64 val)
> > if (little_endian)
> > return (__force __virtio64)cpu_to_le64(val);
> > else
> > - return (__force __virtio64)val;
> > + return (__force __virtio64)cpu_to_be64(val);
> > }
> >
> > #endif /* _LINUX_VIRTIO_BYTEORDER */
> > diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> > index bd1a582..36a6daa 100644
> > --- a/include/linux/virtio_config.h
> > +++ b/include/linux/virtio_config.h
> > @@ -207,7 +207,9 @@ int virtqueue_set_affinity(struct virtqueue *vq, int cpu)
> >
> > static inline bool virtio_is_little_endian(struct virtio_device *vdev)
> > {
> > - return virtio_has_feature(vdev, VIRTIO_F_VERSION_1);
> > + if (virtio_has_feature(vdev, VIRTIO_F_VERSION_1))
> > + return true;
> > + return virtio_legacy_is_little_endian();
> > }
> >
> > /* Memory accessors */
> > diff --git a/include/linux/vringh.h b/include/linux/vringh.h
> > index 3ed62ef..d786c2d 100644
> > --- a/include/linux/vringh.h
> > +++ b/include/linux/vringh.h
> > @@ -228,7 +228,9 @@ static inline void vringh_notify(struct vringh *vrh)
> >
> > static inline bool vringh_is_little_endian(const struct vringh *vrh)
> > {
> > - return vrh->little_endian;
> > + if (vrh->little_endian)
> > + return true;
> > + return virtio_legacy_is_little_endian();
> > }
> >
> > static inline u16 vringh16_to_cpu(const struct vringh *vrh, __virtio16 val)
>