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@xxxxxxxxxx>
---
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;
