tuntap: XDP transmission

This patch implements XDP transmission for TAP. Since we can't create
new queues for TAP during XDP set, exist ptr_ring was reused for
queuing XDP buffers. To differ xdp_buff from sk_buff, TUN_XDP_FLAG
(0x1UL) was encoded into lowest bit of xpd_buff pointer during
ptr_ring_produce, and was decoded during consuming. XDP metadata was
stored in the headroom of the packet which should work in most of
cases since driver usually reserve enough headroom. Very minor changes
were done for vhost_net: it just need to peek the length depends on
the type of pointer.

Tests were done on two Intel E5-2630 2.40GHz machines connected back
to back through two 82599ES. Traffic were generated/received through
MoonGen/testpmd(rxonly). It reports ~20% improvements when
xdp_redirect_map is doing redirection from ixgbe to TAP (from 2.50Mpps
to 3.05Mpps)

Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h
index bdee9b83baf6..08e66827ad8e 100644
--- a/include/linux/if_tun.h
+++ b/include/linux/if_tun.h
@@ -17,9 +17,14 @@
 
 #include <uapi/linux/if_tun.h>
 
+#define TUN_XDP_FLAG 0x1UL
+
 #if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE)
 struct socket *tun_get_socket(struct file *);
 struct ptr_ring *tun_get_tx_ring(struct file *file);
+bool tun_is_xdp_buff(void *ptr);
+void *tun_xdp_to_ptr(void *ptr);
+void *tun_ptr_to_xdp(void *ptr);
 #else
 #include <linux/err.h>
 #include <linux/errno.h>
@@ -33,5 +38,17 @@ static inline struct ptr_ring *tun_get_tx_ring(struct file *f)
 {
 	return ERR_PTR(-EINVAL);
 }
+static inline bool tun_is_xdp_buff(void *ptr)
+{
+	return false;
+}
+void *tun_xdp_to_ptr(void *ptr)
+{
+	return NULL;
+}
+void *tun_ptr_to_xdp(void *ptr)
+{
+	return NULL;
+}
 #endif /* CONFIG_TUN */
 #endif /* __IF_TUN_H */