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Date: Mon, 17 Feb 2020 12:03:38 +0100
From: "Eelco Chaudron" <echaudro@...hat.com>
To: bpf@...r.kernel.org
Cc: davem@...emloft.net, netdev@...r.kernel.org, ast@...nel.org,
daniel@...earbox.net, kafai@...com, songliubraving@...com,
yhs@...com, andriin@...com, toke@...hat.com
Subject: Re: [PATCH bpf-next v3] libbpf: Add support for dynamic program
attach target
!! IGNORE THIS ONE, FORGOR TO UPDATE libbpf.map AS NET-NEXT IS OPEN !!
On 17 Feb 2020, at 12:01, Eelco Chaudron wrote:
> Currently when you want to attach a trace program to a bpf program
> the section name needs to match the tracepoint/function semantics.
>
> However the addition of the bpf_program__set_attach_target() API
> allows you to specify the tracepoint/function dynamically.
>
> The call flow would look something like this:
>
> xdp_fd = bpf_prog_get_fd_by_id(id);
> trace_obj = bpf_object__open_file("func.o", NULL);
> prog = bpf_object__find_program_by_title(trace_obj,
> "fentry/myfunc");
> bpf_program__set_expected_attach_type(prog, BPF_TRACE_FENTRY);
> bpf_program__set_attach_target(prog, xdp_fd,
> "xdpfilt_blk_all");
> bpf_object__load(trace_obj)
>
> Signed-off-by: Eelco Chaudron <echaudro@...hat.com>
> ---
> v1 -> v2: Remove requirement for attach type hint in API
> v2 -> v3: Moved common warning to __find_vmlinux_btf_id, requested by
> Andrii
> Updated the xdp_bpf2bpf test to use this new API
>
> tools/lib/bpf/libbpf.c | 34
> ++++++++++++++++++--
> tools/lib/bpf/libbpf.h | 4 ++
> tools/lib/bpf/libbpf.map | 1 +
> .../testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c | 16 ++++++++-
> .../testing/selftests/bpf/progs/test_xdp_bpf2bpf.c | 4 +-
> 5 files changed, 50 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 514b1a524abb..0c25d78fb5d8 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4939,8 +4939,8 @@ int bpf_program__load(struct bpf_program *prog,
> char *license, __u32 kern_ver)
> {
> int err = 0, fd, i, btf_id;
>
> - if (prog->type == BPF_PROG_TYPE_TRACING ||
> - prog->type == BPF_PROG_TYPE_EXT) {
> + if ((prog->type == BPF_PROG_TYPE_TRACING ||
> + prog->type == BPF_PROG_TYPE_EXT) && !prog->attach_btf_id) {
> btf_id = libbpf_find_attach_btf_id(prog);
> if (btf_id <= 0)
> return btf_id;
> @@ -6583,6 +6583,9 @@ static inline int __find_vmlinux_btf_id(struct
> btf *btf, const char *name,
> else
> err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
>
> + if (err <= 0)
> + pr_warn("%s is not found in vmlinux BTF\n", name);
> +
> return err;
> }
>
> @@ -6655,8 +6658,6 @@ static int libbpf_find_attach_btf_id(struct
> bpf_program *prog)
> err = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
> name + section_defs[i].len,
> attach_type);
> - if (err <= 0)
> - pr_warn("%s is not found in vmlinux BTF\n", name);
> return err;
> }
> pr_warn("failed to identify btf_id based on ELF section name
> '%s'\n", name);
> @@ -8132,6 +8133,31 @@ void bpf_program__bpil_offs_to_addr(struct
> bpf_prog_info_linear *info_linear)
> }
> }
>
> +int bpf_program__set_attach_target(struct bpf_program *prog,
> + int attach_prog_fd,
> + const char *attach_func_name)
> +{
> + int btf_id;
> +
> + if (!prog || attach_prog_fd < 0 || !attach_func_name)
> + return -EINVAL;
> +
> + if (attach_prog_fd)
> + btf_id = libbpf_find_prog_btf_id(attach_func_name,
> + attach_prog_fd);
> + else
> + btf_id = __find_vmlinux_btf_id(prog->obj->btf_vmlinux,
> + attach_func_name,
> + prog->expected_attach_type);
> +
> + if (btf_id <= 0)
> + return btf_id;
> +
> + prog->attach_btf_id = btf_id;
> + prog->attach_prog_fd = attach_prog_fd;
> + return 0;
> +}
> +
> int parse_cpu_mask_str(const char *s, bool **mask, int *mask_sz)
> {
> int err = 0, n, len, start, end = -1;
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 3fe12c9d1f92..02fc58a21a7f 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -334,6 +334,10 @@ LIBBPF_API void
> bpf_program__set_expected_attach_type(struct bpf_program *prog,
> enum bpf_attach_type type);
>
> +LIBBPF_API int
> +bpf_program__set_attach_target(struct bpf_program *prog, int
> attach_prog_fd,
> + const char *attach_func_name);
> +
> LIBBPF_API bool bpf_program__is_socket_filter(const struct
> bpf_program *prog);
> LIBBPF_API bool bpf_program__is_tracepoint(const struct bpf_program
> *prog);
> LIBBPF_API bool bpf_program__is_raw_tracepoint(const struct
> bpf_program *prog);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index b035122142bb..8aba5438a3f0 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -230,6 +230,7 @@ LIBBPF_0.0.7 {
> bpf_program__name;
> bpf_program__is_extension;
> bpf_program__is_struct_ops;
> + bpf_program__set_attach_target;
> bpf_program__set_extension;
> bpf_program__set_struct_ops;
> btf__align_of;
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
> b/tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
> index 6b56bdc73ebc..513fdbf02b81 100644
> --- a/tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_bpf2bpf.c
> @@ -14,7 +14,7 @@ void test_xdp_bpf2bpf(void)
> struct test_xdp *pkt_skel = NULL;
> struct test_xdp_bpf2bpf *ftrace_skel = NULL;
> struct vip key4 = {.protocol = 6, .family = AF_INET};
> - DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
> + struct bpf_program *prog;
>
> /* Load XDP program to introspect */
> pkt_skel = test_xdp__open_and_load();
> @@ -27,11 +27,21 @@ void test_xdp_bpf2bpf(void)
> bpf_map_update_elem(map_fd, &key4, &value4, 0);
>
> /* Load trace program */
> - opts.attach_prog_fd = pkt_fd,
> - ftrace_skel = test_xdp_bpf2bpf__open_opts(&opts);
> + ftrace_skel = test_xdp_bpf2bpf__open();
> if (CHECK(!ftrace_skel, "__open", "ftrace skeleton failed\n"))
> goto out;
>
> + /* Demonstrate the bpf_program__set_attach_target() API rather than
> + * the load with options, i.e. opts.attach_prog_fd.
> + */
> + prog = *ftrace_skel->skeleton->progs[0].prog;
> + bpf_program__set_expected_attach_type(prog, BPF_TRACE_FENTRY);
> + bpf_program__set_attach_target(prog, pkt_fd, "_xdp_tx_iptunnel");
> +
> + prog = *ftrace_skel->skeleton->progs[1].prog;
> + bpf_program__set_expected_attach_type(prog, BPF_TRACE_FEXIT);
> + bpf_program__set_attach_target(prog, pkt_fd, "_xdp_tx_iptunnel");
> +
> err = test_xdp_bpf2bpf__load(ftrace_skel);
> if (CHECK(err, "__load", "ftrace skeleton failed\n"))
> goto out;
> diff --git a/tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
> b/tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
> index cb8a04ab7a78..b840fc9e3ed5 100644
> --- a/tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
> +++ b/tools/testing/selftests/bpf/progs/test_xdp_bpf2bpf.c
> @@ -28,7 +28,7 @@ struct xdp_buff {
> } __attribute__((preserve_access_index));
>
> __u64 test_result_fentry = 0;
> -SEC("fentry/_xdp_tx_iptunnel")
> +SEC("fentry/FUNC")
> int BPF_PROG(trace_on_entry, struct xdp_buff *xdp)
> {
> test_result_fentry = xdp->rxq->dev->ifindex;
> @@ -36,7 +36,7 @@ int BPF_PROG(trace_on_entry, struct xdp_buff *xdp)
> }
>
> __u64 test_result_fexit = 0;
> -SEC("fexit/_xdp_tx_iptunnel")
> +SEC("fexit/FUNC")
> int BPF_PROG(trace_on_exit, struct xdp_buff *xdp, int ret)
> {
> test_result_fexit = ret;
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