samples/bpf: split common macros to net_shared.h

Currently, many programs under sample/bpf often include individual
macros by directly including the header under "linux/" rather than
using the "vmlinux.h" header.

However, there are some problems with migrating to "vmlinux.h" because
there is no definition for utility functions such as endianness
conversion (ntohs/htons). Fortunately, the xdp_sample program already
has a function that can be replaced to solve this problem.

Therefore, this commit attempts to separate these functions into a file
called net_shared.h to make them universally available. Additionally,
this file includes network-related macros that are not defined in
"vmlinux.h". (inspired by 'selftests' bpf_tracing_net.h)

Signed-off-by: Daniel T. Lee <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

samples/bpf/net_shared.h

···
+// SPDX-License-Identifier: GPL-2.0
+#ifndef _NET_SHARED_H
+#define _NET_SHARED_H
+
+#define ETH_ALEN 6
+#define ETH_P_802_3_MIN 0x0600
+#define ETH_P_8021Q 0x8100
+#define ETH_P_8021AD 0x88A8
+#define ETH_P_IP 0x0800
+#define ETH_P_IPV6 0x86DD
+#define ETH_P_ARP 0x0806
+#define IPPROTO_ICMPV6 58
+
+#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && \
+	__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define bpf_ntohs(x)		__builtin_bswap16(x)
+#define bpf_htons(x)		__builtin_bswap16(x)
+#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && \
+	__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#define bpf_ntohs(x)		(x)
+#define bpf_htons(x)		(x)
+#else
+# error "Endianness detection needs to be set up for your compiler?!"
+#endif
+
+#endif

samples/bpf/xdp_sample.bpf.h

···
 #include <bpf/bpf_core_read.h>
 #include <bpf/bpf_helpers.h>
 
+#include "net_shared.h"
 #include "xdp_sample_shared.h"
-
-#define ETH_ALEN 6
-#define ETH_P_802_3_MIN 0x0600
-#define ETH_P_8021Q 0x8100
-#define ETH_P_8021AD 0x88A8
-#define ETH_P_IP 0x0800
-#define ETH_P_IPV6 0x86DD
-#define ETH_P_ARP 0x0806
-#define IPPROTO_ICMPV6 58
 
 #define EINVAL 22
 #define ENETDOWN 100
···
 	p[4] = dst[1];
 	p[5] = dst[2];
 }
-
-#if defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && \
-	__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
-#define bpf_ntohs(x)		__builtin_bswap16(x)
-#define bpf_htons(x)		__builtin_bswap16(x)
-#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && \
-	__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
-#define bpf_ntohs(x)		(x)
-#define bpf_htons(x)		(x)
-#else
-# error "Endianness detection needs to be set up for your compiler?!"
-#endif
 
 /*
  * Note: including linux/compiler.h or linux/kernel.h for the macros below