netdev - [PATCH bpf-next] bpf_helpers.h: Add note for building with vmlinux.h or linux/types.h

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Message-Id: <1587427527-29399-1-git-send-email-komachi.yoshiki@gmail.com>
Date:   Tue, 21 Apr 2020 09:05:27 +0900
From:   Yoshiki Komachi <komachi.yoshiki@...il.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>
Cc:     Yoshiki Komachi <komachi.yoshiki@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH bpf-next] bpf_helpers.h: Add note for building with vmlinux.h or linux/types.h

The following error was shown when a bpf program was compiled without
vmlinux.h auto-generated from BTF:

 # clang -I./linux/tools/lib/ -I/lib/modules/$(uname -r)/build/include/ \
   -O2 -Wall -target bpf -emit-llvm -c bpf_prog.c -o bpf_prog.bc
 ...
 In file included from linux/tools/lib/bpf/bpf_helpers.h:5:
 linux/tools/lib/bpf/bpf_helper_defs.h:56:82: error: unknown type name '__u64'
 ...

It seems that bpf programs are intended for being built together with
the vmlinux.h (which will have all the __u64 and other typedefs). But
users may mistakenly think "include <linux/types.h>" is missing
because the vmlinux.h is not common for non-bpf developers. IMO, an
explicit comment therefore should be added to bpf_helpers.h as this
patch shows.

Signed-off-by: Yoshiki Komachi <komachi.yoshiki@...il.com>
---
 tools/lib/bpf/bpf_helpers.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index f69cc208778a..60aad054eea1 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -2,6 +2,12 @@
 #ifndef __BPF_HELPERS__
 #define __BPF_HELPERS__
 
+/*
+ * Note that bpf programs need to include either
+ * vmlinux.h (auto-generated from BTF) or linux/types.h
+ * in advance since bpf_helper_defs.h uses such types
+ * as __u64.
+ */
 #include "bpf_helper_defs.h"
 
 #define __uint(name, val) int (*name)[val]
-- 
2.24.1