On 18 Feb 2020, at 22:24, Andrii Nakryiko wrote:
On Tue, Feb 18, 2020 at 8:34 AM Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
wrote:
Hey Eelco,
On Mon, Feb 17, 2020 at 12:43 PM GMT, 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)
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
Signed-off-by: Eelco Chaudron <echaudro@xxxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 34 ++++++++++++++++++++++++++++++----
tools/lib/bpf/libbpf.h | 4 ++++
tools/lib/bpf/libbpf.map | 2 ++
3 files changed, 36 insertions(+), 4 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
[...]
@@ -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;
Looks like we can get 0 as return value on both error and success
(below)? Is that intentional?
Neither libbpf_find_prog_btf_id nor __find_vmlinux_btf_id are going to
return 0 on failure. But I do agree that if (btf_id < 0) check would
be better here.
Is see in theory btf__find_by_name_kind() could return 0:
if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
return 0;
But for our case, this will not happen and is invalid, so what about
just to make sure its future proof?:
if (btf_id <= 0)
return btf_id ? btf_id : -ENOENT;
With that minor nit:
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
+
+ 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;
[...]
