Re: [PATCH v4 8/8] macvtap/tun: add VNET_BE flag

Michael S. Tsirkin
2015-04-21T14:06:39Z

On Fri, Apr 10, 2015 at 12:20:21PM +0200, Greg Kurz wrote:
> The VNET_LE flag was introduced to fix accesses to virtio 1.0 headers
> that are always little-endian. It can also be used to handle the special
> case of a legacy little-endian device implemented by a big-endian host.
>
> Let's add a flag and ioctls for big-endian devices as well. If both flags
> are set, little-endian wins.
>
> Since this is isn't a common usecase, the feature is controlled by a kernel
> config option (not set by default).
>
> Both macvtap and tun are covered by this patch since they share the same
> API with userland.
>
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
> drivers/net/Kconfig | 12 ++++++++
> drivers/net/macvtap.c | 60 +++++++++++++++++++++++++++++++++++++++++-
> drivers/net/tun.c | 62 ++++++++++++++++++++++++++++++++++++++++++-
> include/uapi/linux/if_tun.h | 2 +
> 4 files changed, 134 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index df51d60..f0e23a0 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -244,6 +244,18 @@ config TUN
>
> If you don't know what to use this for, you don't need it.
>
> +config TUN_VNET_BE
> + bool "Support for big-endian vnet headers"
> + default n
> + ---help---
> + This option allows TUN/TAP and MACVTAP device drivers to parse
> + vnet headers that are in big-endian byte order. It is useful
> + when the headers come from a big-endian legacy virtio driver and
> + the host is little-endian.
> +
> + Unless you have a little-endian system hosting a big-endian virtual
> + machine with a virtio NIC, you should say N.
> +

should mention cross-endian, not big-endian, right?

> config VETH
> tristate "Virtual ethernet pair device"
> ---help---
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 0a03a66..e0ab1b7 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -48,12 +48,27 @@ struct macvtap_queue {
> #define MACVTAP_FEATURES (IFF_VNET_HDR | IFF_MULTI_QUEUE)
>
> #define MACVTAP_VNET_LE 0x80000000
> +#define MACVTAP_VNET_BE 0x40000000
> +
> +#ifdef CONFIG_TUN_VNET_BE
> +static inline bool macvtap_legacy_is_little_endian(struct macvtap_queue *q)
> +{
> + if (q->flags & MACVTAP_VNET_BE)
> + return false;
> + return virtio_legacy_is_little_endian();
> +}
> +#else
> +static inline bool macvtap_legacy_is_little_endian(struct macvtap_queue *q)
> +{
> + return virtio_legacy_is_little_endian();
> +}
> +#endif
>
> static inline bool macvtap_is_little_endian(struct macvtap_queue *q)
> {
> if (q->flags & MACVTAP_VNET_LE)
> return true;
> - return virtio_legacy_is_little_endian();
> + return macvtap_legacy_is_little_endian(q);
> }
>
> static inline u16 macvtap16_to_cpu(struct macvtap_queue *q, __virtio16 val)
> @@ -1000,6 +1015,43 @@ static int set_offload(struct macvtap_queue *q, unsigned long arg)
> return 0;
> }
>
> +#ifdef CONFIG_TUN_VNET_BE
> +static long macvtap_get_vnet_be(struct macvtap_queue *q, int __user *sp)
> +{
> + int s = !!(q->flags & MACVTAP_VNET_BE);
> +
> + if (put_user(s, sp))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
> +static long macvtap_set_vnet_be(struct macvtap_queue *q, int __user *sp)
> +{
> + int s;
> +
> + if (get_user(s, sp))
> + return -EFAULT;
> +
> + if (s)
> + q->flags |= MACVTAP_VNET_BE;
> + else
> + q->flags &= ~MACVTAP_VNET_BE;
> +
> + return 0;
> +}
> +#else
> +static long macvtap_get_vnet_be(struct macvtap_queue *q, int __user *argp)
> +{
> + return -EINVAL;
> +}
> +
> +static long macvtap_set_vnet_be(struct macvtap_queue *q, int __user *argp)
> +{
> + return -EINVAL;
> +}
> +#endif /* CONFIG_TUN_VNET_BE */
> +
> /*
> * provide compatibility with generic tun/tap interface
> */
> @@ -1097,6 +1149,12 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
> q->flags &= ~MACVTAP_VNET_LE;
> return 0;
>
> + case TUNGETVNETBE:
> + return macvtap_get_vnet_be(q, sp);
> +
> + case TUNSETVNETBE:
> + return macvtap_set_vnet_be(q, sp);
> +
> case TUNSETOFFLOAD:
> /* let the user check for future flags */
> if (arg & ~(TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6 |
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 053f9b6..4e12488 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -111,6 +111,7 @@ do { \
> #define TUN_FASYNC IFF_ATTACH_QUEUE
> /* High bits in flags field are unused. */
> #define TUN_VNET_LE 0x80000000
> +#define TUN_VNET_BE 0x40000000
>
> #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
> IFF_MULTI_QUEUE)
> @@ -206,11 +207,25 @@ struct tun_struct {
> u32 flow_count;
> };
>
> +#ifdef CONFIG_TUN_VNET_BE
> +static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
> +{
> + if (tun->flags & TUN_VNET_BE)
> + return false;
> + return virtio_legacy_is_little_endian();
> +}
> +#else
> +static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
> +{
> + return virtio_legacy_is_little_endian();
> +}
> +#endif
> +
> static inline bool tun_is_little_endian(struct tun_struct *tun)
> {
> if (tun->flags & TUN_VNET_LE)
> return true;
> - return virtio_legacy_is_little_endian();
> + return tun_legacy_is_little_endian(tun);
> }
>
> static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
> @@ -1836,6 +1851,43 @@ unlock:
> return ret;
> }
>
> +#ifdef CONFIG_TUN_VNET_BE
> +static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
> +{
> + int be = !!(tun->flags & TUN_VNET_BE);
> +
> + if (put_user(be, argp))
> + return EFAULT;
> +
> + return 0;
> +}
> +
> +static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
> +{
> + int be;
> +
> + if (get_user(be, argp))
> + return -EFAULT;
> +
> + if (be)
> + tun->flags |= TUN_VNET_BE;
> + else
> + tun->flags &= ~TUN_VNET_BE;
> +
> + return 0;
> +}
> +#else
> +static long tun_get_vnet_be(struct tun_struct *tun, int __user *argp)
> +{
> + return -EINVAL;
> +}
> +
> +static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
> +{
> + return -EINVAL;
> +}
> +#endif /* CONFIG_TUN_VNET_BE */
> +
> static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
> unsigned long arg, int ifreq_len)
> {
> @@ -2065,6 +2117,14 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
> tun->flags &= ~TUN_VNET_LE;
> break;
>
> + case TUNGETVNETBE:
> + ret = tun_get_vnet_be(tun, argp);
> + break;
> +
> + case TUNSETVNETBE:
> + ret = tun_set_vnet_be(tun, argp);
> + break;
> +
> case TUNATTACHFILTER:
> /* Can be set only for TAPs */
> ret = -EINVAL;
> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index 50ae243..bcac4c0 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -50,6 +50,8 @@
> #define TUNGETFILTER _IOR('T', 219, struct sock_fprog)
> #define TUNSETVNETLE _IOW('T', 220, int)
> #define TUNGETVNETLE _IOR('T', 221, int)
> +#define TUNSETVNETBE _IOW('T', 222, int)
> +#define TUNGETVNETBE _IOR('T', 223, int)
>
> /* TUNSETIFF ifr flags */
> #define IFF_TUN 0x0001