Michal reported a build failure likes below:
   BTFIDS  vmlinux
   FAILED unresolved symbol tcp_timewait_sock
   make[1]: *** [/.../linux-5.9-rc7/Makefile:1176: vmlinux] Error 255

This error can be triggered when config has CONFIG_NET enabled
but CONFIG_INET disabled. In this case, there is no user of
structs inet_timewait_sock and tcp_timewait_sock and hence vmlinux BTF
types are not generated for these two structures.

To fix the problem, omit the above two types for BTF_SOCK_TYPE_xxx
macro if CONFIG_INET is not defined.

Fixes: fce557bcef11 ("bpf: Make btf_sock_ids global")
Reported-by: Michal Kubecek <redacted>
Signed-off-by: Yonghong Song <redacted>
---
 include/linux/btf_ids.h | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
index 4867d549e3c1..d9a1e18d0921 100644
--- a/include/linux/btf_ids.h
+++ b/include/linux/btf_ids.h

@@ -102,24 +102,36 @@ asm(                                                      \
  * skc_to_*_sock() helpers. All these sockets should have
  * sock_common as the first argument in its memory layout.
  */
-#define BTF_SOCK_TYPE_xxx \
+
+#define __BTF_SOCK_TYPE_xxx \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET, inet_sock)                    \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_CONN, inet_connection_sock)    \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_REQ, inet_request_sock)        \
-       BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, inet_timewait_sock)        \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_REQ, request_sock)                  \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK, sock)                         \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_SOCK_COMMON, sock_common)           \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP, tcp_sock)                      \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_REQ, tcp_request_sock)          \
-       BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)          \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, tcp6_sock)                    \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, udp_sock)                      \
        BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)

+#define __BTF_SOCK_TW_TYPE_xxx \
+       BTF_SOCK_TYPE(BTF_SOCK_TYPE_INET_TW, inet_timewait_sock)        \
+       BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)
+
+#ifdef CONFIG_INET
+#define BTF_SOCK_TYPE_xxx                                              \
+       __BTF_SOCK_TYPE_xxx                                             \
+       __BTF_SOCK_TW_TYPE_xxx
+#else
+#define BTF_SOCK_TYPE_xxx      __BTF_SOCK_TYPE_xxx
+#endif
+
 enum {
 #define BTF_SOCK_TYPE(name, str) name,
-BTF_SOCK_TYPE_xxx
+__BTF_SOCK_TYPE_xxx
+__BTF_SOCK_TW_TYPE_xxx