net-tun: Add type safety to tun_xdp_to_ptr() and tun_ptr_to_xdp()

This reduces likelihood of incorrect use.

Test: builds
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200819010710.3959310-1-zenczykowski@gmail.com

drivers/net/tun.c

@@ -225,13 +225,13 @@ bool tun_is_xdp_frame(void *ptr)
 }
 EXPORT_SYMBOL(tun_is_xdp_frame);
 
-void *tun_xdp_to_ptr(void *ptr)
+void *tun_xdp_to_ptr(struct xdp_frame *xdp)
 {
-	return (void *)((unsigned long)ptr | TUN_XDP_FLAG);
+	return (void *)((unsigned long)xdp | TUN_XDP_FLAG);
 }
 EXPORT_SYMBOL(tun_xdp_to_ptr);
 
-void *tun_ptr_to_xdp(void *ptr)
+struct xdp_frame *tun_ptr_to_xdp(void *ptr)
 {
 	return (void *)((unsigned long)ptr & ~TUN_XDP_FLAG);
 }

include/linux/if_tun.h

@@ -28,8 +28,8 @@ struct tun_xdp_hdr {
 struct socket *tun_get_socket(struct file *);
 struct ptr_ring *tun_get_tx_ring(struct file *file);
 bool tun_is_xdp_frame(void *ptr);
-void *tun_xdp_to_ptr(void *ptr);
-void *tun_ptr_to_xdp(void *ptr);
+void *tun_xdp_to_ptr(struct xdp_frame *xdp);
+struct xdp_frame *tun_ptr_to_xdp(void *ptr);
 void tun_ptr_free(void *ptr);
 #else
 #include <linux/err.h>
@@ -48,11 +48,11 @@ static inline bool tun_is_xdp_frame(void *ptr)
 {
 	return false;
 }
-static inline void *tun_xdp_to_ptr(void *ptr)
+static inline void *tun_xdp_to_ptr(struct xdp_frame *xdp)
 {
 	return NULL;
 }
-static inline void *tun_ptr_to_xdp(void *ptr)
+static inline struct xdp_frame *tun_ptr_to_xdp(void *ptr)
 {
 	return NULL;
 }