On 13 Feb 2020, at 18:42, Andrii Nakryiko wrote:
On Thu, Feb 13, 2020 at 7:05 AM Eelco Chaudron <echaudro@xxxxxxxxxx>
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@xxxxxxxxxx>
---
API-wise this looks good, thanks! Please address feedback below and
re-submit once bpf-next opens. Can you please also convert one of
existing selftests using open_opts's attach_prog_fd to use this API
instead to have a demonstration there?
Yes will update the one I added for bfp2bpf testing…
v1 -> v2: Remove requirement for attach type name in API
tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++++++--
tools/lib/bpf/libbpf.h | 4 ++++
tools/lib/bpf/libbpf.map | 1 +
3 files changed, 36 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 514b1a524abb..9b8cab995580 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;
@@ -8132,6 +8132,35 @@ 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) {
+ if (!attach_prog_fd)
+ pr_warn("%s is not found in vmlinux BTF\n",
+ attach_func_name);
libbpf_find_attach_btf_id's error reporting is misleading (it always
reports as if error happened with vmlinux BTF, even if attach_prog_fd
0). Could you please fix that and add better error reporting here
for attach_prog_fd>0 case here?
I did not add log messages for the btf_id > 0 case as they are covered
in the libbpf_find_prog_btf_id() function. Please let me know if this is
not enough.
+ 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;
This will have to go into LIBBPF_0.0.8 once bpf-next opens. Please
rebase and re-send then.
Will do…
bpf_program__set_extension;
bpf_program__set_struct_ops;
btf__align_of;
