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Commit 8b8e658b authored by Greg Kurz's avatar Greg Kurz Committed by Michael S. Tsirkin
Browse files

macvtap/tun: cross-endian support for little-endian hosts 



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: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>

Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
parent 2751c988

drivers/net/Kconfig

+14 −0
Original line number Diff line number Diff line
@@ -244,6 +244,20 @@ config TUN 


	  If you don't know what to use this for, you don't need it.



config TUN_VNET_CROSS_LE

	bool "Support for cross-endian vnet headers on little-endian kernels"

	default n

	---help---

	  This option allows TUN/TAP and MACVTAP device drivers in a

	  little-endian kernel to parse vnet headers that come from a

	  big-endian legacy virtio device.



	  Userspace programs can control the feature using the TUNSETVNETBE

	  and TUNGETVNETBE ioctls.



	  Unless you have a little-endian system hosting a big-endian virtual

	  machine with a legacy virtio NIC, you should say N.



config VETH

	tristate "Virtual ethernet pair device"

	---help---

drivers/net/macvtap.c

+56 −1
Original line number Diff line number Diff line
@@ -48,11 +48,60 @@ 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_CROSS_LE

static inline bool macvtap_legacy_is_little_endian(struct macvtap_queue *q)

{

	return q->flags & MACVTAP_VNET_BE ? false :

		virtio_legacy_is_little_endian();

}



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 inline bool macvtap_legacy_is_little_endian(struct macvtap_queue *q)

{

	return virtio_legacy_is_little_endian();

}



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_CROSS_LE */



static inline bool macvtap_is_little_endian(struct macvtap_queue *q)

{

	return q->flags & MACVTAP_VNET_LE ||

		virtio_legacy_is_little_endian();

		macvtap_legacy_is_little_endian(q);

}



static inline u16 macvtap16_to_cpu(struct macvtap_queue *q, __virtio16 val)
@@ -1096,6 +1145,12 @@ 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 |

drivers/net/tun.c

+58 −1
Original line number Diff line number Diff line
@@ -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)
@@ -206,10 +207,58 @@ struct tun_struct { 
	u32 flow_count;

};



#ifdef CONFIG_TUN_VNET_CROSS_LE

static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)

{

	return tun->flags & TUN_VNET_BE ? false :

		virtio_legacy_is_little_endian();

}



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 inline bool tun_legacy_is_little_endian(struct tun_struct *tun)

{

	return virtio_legacy_is_little_endian();

}



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_CROSS_LE */



static inline bool tun_is_little_endian(struct tun_struct *tun)

{

	return tun->flags & TUN_VNET_LE ||

		virtio_legacy_is_little_endian();

		tun_legacy_is_little_endian(tun);

}



static inline u16 tun16_to_cpu(struct tun_struct *tun, __virtio16 val)
@@ -2062,6 +2111,14 @@ 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;

include/uapi/linux/if_tun.h

+6 −0
Original line number Diff line number Diff line
@@ -50,6 +50,12 @@ 
#define TUNGETFILTER _IOR('T', 219, struct sock_fprog)

#define TUNSETVNETLE _IOW('T', 220, int)

#define TUNGETVNETLE _IOR('T', 221, int)

/* The TUNSETVNETBE and TUNGETVNETBE ioctls are for cross-endian support on

 * little-endian hosts. Not all kernel configurations support them, but all

 * configurations that support SET also support GET.

 */

#define TUNSETVNETBE _IOW('T', 222, int)

#define TUNGETVNETBE _IOR('T', 223, int)



/* TUNSETIFF ifr flags */

#define IFF_TUN		0x0001