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Subject[PATCH v4 8/8] macvtap/tun: add VNET_BE flag
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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.
+
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


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