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From:   Rong Tao <rtoax@foxmail.com>
To:     andrii.nakryiko@gmail.com
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Subject: Re: Re: [PATCH bpf-next] samples/bpf: Fix sockex3: missing BPF prog type
Date:   Fri,  4 Nov 2022 11:17:13 +0800
In-Reply-To: <CAEf4BzbvCABmSB3UqKyka=txTiCUdBpTtQg4X6XOa_qVVXW+hw@mail.gmail.com>
References: <CAEf4BzbvCABmSB3UqKyka=txTiCUdBpTtQg4X6XOa_qVVXW+hw@mail.gmail.com>
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We can not just remove the number of program like:

-#define PROG(F) SEC("socket/"__stringify(F)) int bpf_func_##F
+#define PROG(F) SEC("socket_filter") int bpf_func_##F

because "sockex3" use the _NUMBER_ as index(see map "jmp_table"), if we
apply the following patch, it's still not recognize "socket_filter/xxx"
as "socket_filter", still have "missing BPF prog type" error:

diff --git a/samples/bpf/sockex3_kern.c b/samples/bpf/sockex3_kern.c
index b363503357e5..ab5a7bde66d0 100644
--- a/samples/bpf/sockex3_kern.c
+++ b/samples/bpf/sockex3_kern.c
@@ -17,7 +17,7 @@
 #define IP_MF          0x2000
 #define IP_OFFSET      0x1FFF

-#define PROG(F) SEC("socket/"__stringify(F)) int bpf_func_##F
+#define PROG(F) SEC("socket_filter/"__stringify(F)) int bpf_func_##F

 struct {
        __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
@@ -279,7 +279,7 @@ PROG(PARSE_MPLS)(struct __sk_buff *skb)
        return 0;
 }

-SEC("socket/0")
+SEC("socket_filter/0")
 int main_prog(struct __sk_buff *skb)
 {
        __u32 nhoff = ETH_HLEN;
diff --git a/samples/bpf/sockex3_user.c b/samples/bpf/sockex3_user.c
index cd6fa79df900..63fc9a8077b1 100644
--- a/samples/bpf/sockex3_user.c
+++ b/samples/bpf/sockex3_user.c
@@ -56,7 +56,7 @@ int main(int argc, char **argv)
                fd = bpf_program__fd(prog);

                section = bpf_program__section_name(prog);
-               if (sscanf(section, "socket/%d", &key) != 1) {
+               if (sscanf(section, "socket_filter/%d", &key) != 1) {
                        fprintf(stderr, "ERROR: finding prog failed\n");
                        goto cleanup;
                }

For a reason, in sockex3_kern.c only have five PROGs, list all five:

#define PROG(F) SEC("socket/"__stringify(F)) int bpf_func_##F
PROG(PARSE_IP)(struct __sk_buff *skb)
PROG(PARSE_IPV6)(struct __sk_buff *skb)
PROG(PARSE_VLAN)(struct __sk_buff *skb)
PROG(PARSE_MPLS)(struct __sk_buff *skb)
SEC("socket/0") int main_prog(struct __sk_buff *skb)

As you can see, all those PROGs are BPF_PROG_TYPE_SOCKET_FILTER, so we can
use the follow patch specify bpf program type as SOCKET_FILTER:

https://lore.kernel.org/lkml/tencent_7DD02046A8398BE3324F85E0F56ED41EB105@qq.com/

diff --git a/samples/bpf/sockex3_user.c b/samples/bpf/sockex3_user.c
index cd6fa79df900..dc79c17ad195 100644
--- a/samples/bpf/sockex3_user.c
+++ b/samples/bpf/sockex3_user.c
@@ -39,6 +39,9 @@ int main(int argc, char **argv)
                return 0;
        }

+       bpf_object__for_each_program(prog, obj)
+               bpf_program__set_type(prog, BPF_PROG_TYPE_SOCKET_FILTER);
+
        /* load BPF program */
        if (bpf_object__load(obj)) {
                fprintf(stderr, "ERROR: loading BPF object file failed\n");

This patch above totally solved the compile error.