[PATCH bpf-next v3] libbpf: fix compilation errors on ubuntu 16.04

* [PATCH bpf-next v3] libbpf: fix compilation errors on ubuntu 16.04
@ 2021-07-12 19:20 Yonghong Song
  2021-07-12 19:25 ` John Fastabend
  2021-07-12 19:26 ` Daniel Borkmann
  0 siblings, 2 replies; 4+ messages in thread
From: Yonghong Song @ 2021-07-12 19:20 UTC (permalink / raw)
  To: bpf
  Cc: Alexei Starovoitov, Andrii Nakryiko, Daniel Borkmann,
	kernel-team, Kumar Kartikeya Dwivedi

libbpf is used as a submodule in bcc.
When importing latest libbpf repo in bcc, I observed the
following compilation errors when compiling on ubuntu 16.04.
  .../netlink.c:416:23: error: ‘TC_H_CLSACT’ undeclared (first use in this function)
     *parent = TC_H_MAKE(TC_H_CLSACT,
                         ^
  .../netlink.c:418:9: error: ‘TC_H_MIN_INGRESS’ undeclared (first use in this function)
           TC_H_MIN_INGRESS : TC_H_MIN_EGRESS);
           ^
  .../netlink.c:418:28: error: ‘TC_H_MIN_EGRESS’ undeclared (first use in this function)
           TC_H_MIN_INGRESS : TC_H_MIN_EGRESS);
                              ^
  .../netlink.c: In function ‘__get_tc_info’:
  .../netlink.c:522:11: error: ‘TCA_BPF_ID’ undeclared (first use in this function)
    if (!tbb[TCA_BPF_ID])
             ^

In ubuntu 16.04, TCA_BPF_* enumerator looks like below
  enum {
	TCA_BPF_UNSPEC,
	TCA_BPF_ACT,
	...
	TCA_BPF_NAME,
	TCA_BPF_FLAGS,
	__TCA_BPF_MAX,
  };
  #define TCA_BPF_MAX	(__TCA_BPF_MAX - 1)
while in latest bpf-next, the enumerator looks like
  enum {
	TCA_BPF_UNSPEC,
	...
	TCA_BPF_FLAGS,
	TCA_BPF_FLAGS_GEN,
	TCA_BPF_TAG,
	TCA_BPF_ID,
	__TCA_BPF_MAX,
  };

In this patch, TCA_BPF_ID is defined as a macro with proper value and this
works regardless of whether TCA_BPF_ID is defined in uapi header or not.
TCA_BPF_MAX is also adjusted in a similar way.

Fixes: 715c5ce454a6 ("libbpf: Add low level TC-BPF management API")
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 tools/lib/bpf/netlink.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

Changelog:
  v2 -> v3:
    - define/redefine TCA_BPF_MAX based on latest uapi header.
      this enables to remove the v2 check "TCA_BPF_MAX < TCA_BPF_ID"
      in __get_tc_info() which may cause -EOPNOTSUPP error
      if the library is compiled in old system and used in
      newer system.
      
  v1 -> v2:
    - gcc 8.3 doesn't like macro condition
        (__TCA_BPF_MAX - 1) <= 10
      where __TCA_BPF_MAX is an enumerator value.
      So define TCA_BPF_ID macro without macro condition.

diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 39f25e09b51e..37cb6b50f4b3 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -22,6 +22,29 @@
 #define SOL_NETLINK 270
 #endif
 
+#ifndef TC_H_CLSACT
+#define TC_H_CLSACT TC_H_INGRESS
+#endif
+
+#ifndef TC_H_MIN_INGRESS
+#define TC_H_MIN_INGRESS 0xFFF2U
+#endif
+
+#ifndef TC_H_MIN_EGRESS
+#define TC_H_MIN_EGRESS 0xFFF3U
+#endif
+
+/* TCA_BPF_ID is an enumerator value in uapi/linux/pkt_cls.h.
+ * Declare it as a macro here so old system can still work
+ * without TCA_BPF_ID defined in pkt_cls.h.
+ */
+#define TCA_BPF_ID 11
+
+#ifdef TCA_BPF_MAX
+#undef TCA_BPF_MAX
+#endif
+#define TCA_BPF_MAX 11
+
 typedef int (*libbpf_dump_nlmsg_t)(void *cookie, void *msg, struct nlattr **tb);
 
 typedef int (*__dump_nlmsg_t)(struct nlmsghdr *nlmsg, libbpf_dump_nlmsg_t,
-- 
2.30.2


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