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Date: Fri, 14 Feb 2020 08:34:28 +0100
From: "Eelco Chaudron" <echaudro@...hat.com>
To: "Andrii Nakryiko" <andrii.nakryiko@...il.com>
Cc: bpf <bpf@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
Networking <netdev@...r.kernel.org>,
"Alexei Starovoitov" <ast@...nel.org>,
"Daniel Borkmann" <daniel@...earbox.net>,
"Martin Lau" <kafai@...com>, "Song Liu" <songliubraving@...com>,
"Yonghong Song" <yhs@...com>, "Andrii Nakryiko" <andriin@...com>,
"Toke Høiland-Jørgensen" <toke@...hat.com>
Subject: Re: [PATCH bpf-next v2] libbpf: Add support for dynamic program
attach target
On 13 Feb 2020, at 18:42, Andrii Nakryiko wrote:
> On Thu, Feb 13, 2020 at 7:05 AM Eelco Chaudron <echaudro@...hat.com>
> 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>
>> ---
>
> 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;
>>
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