tun: enable gso over UDP tunnel support.

Add new tun features to represent the newly introduced virtio
GSO over UDP tunnel offload. Allows detection and selection of
such features via the existing TUNSETOFFLOAD ioctl and compute
the expected virtio header size and tunnel header offset using
the current netdev features, so that we can plug almost seamless
the newly introduced virtio helpers to serialize the extended
virtio header.

Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v6 -> v7:
  - rebased

v4 -> v5:
  - encapsulate the guest feature guessing in a tun helper
  - dropped irrelevant check on xdp buff headroom
  - do not remove unrelated black line
  - avoid line len > 80 char

v3 -> v4:
  - virtio tnl-related fields are at fixed offset, cleanup
    the code accordingly.
  - use netdev features instead of flags bit to check for
    the configured offload
  - drop packet in case of enabled features/configured hdr
    size mismatch

v2 -> v3:
  - cleaned-up uAPI comments
  - use explicit struct layout instead of raw buf.

1 files changed, 9 insertions, 0 deletions

diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 287cdc81c939..79d53c7a1ebd 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -93,6 +93,15 @@
 #define TUN_F_USO4	0x20	/* I can handle USO for IPv4 packets */
 #define TUN_F_USO6	0x40	/* I can handle USO for IPv6 packets */
 
+/* I can handle TSO/USO for UDP tunneled packets */
+#define TUN_F_UDP_TUNNEL_GSO		0x080
+
+/*
+ * I can handle TSO/USO for UDP tunneled packets requiring csum offload for
+ * the outer header
+ */
+#define TUN_F_UDP_TUNNEL_GSO_CSUM	0x100
+
 /* Protocol info prepended to the packets (when IFF_NO_PI is not set) */
 #define TUN_PKT_STRIP	0x0001
 struct tun_pi {