Subject: Re: [PATCH bpf-next 6/8] libbpf: Add support for bpf_link-based netns attachment

From: Jakub Sitnicki <[email-masked]>
Date: Thu, 28 May 2020 15:05:50 +0200

On Thu, May 28, 2020 at 07:59 AM CEST, Andrii Nakryiko wrote:
> On Wed, May 27, 2020 at 12:16 PM Jakub Sitnicki <[email-masked]> wrote:
>>
>> Add bpf_program__attach_nets(), which uses LINK_CREATE subcommand to create
>> an FD-based kernel bpf_link, for attach types tied to network namespace,
>> that is BPF_FLOW_DISSECTOR for the moment.
>>
>> Signed-off-by: Jakub Sitnicki <[email-masked]>
>> ---
>>  tools/lib/bpf/libbpf.c   | 20 ++++++++++++++++----
>>  tools/lib/bpf/libbpf.h   |  2 ++
>>  tools/lib/bpf/libbpf.map |  1 +
>>  3 files changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 5d60de6fd818..a49c1eb5db64 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7894,8 +7894,8 @@ static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
>>         return bpf_program__attach_iter(prog, NULL);
>>  }
>>
>> -struct bpf_link *
>> -bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>> +static struct bpf_link *
>> +bpf_program__attach_fd(struct bpf_program *prog, int target_fd)
>>  {
>>         enum bpf_attach_type attach_type;
>>         char errmsg[STRERR_BUFSIZE];
>> @@ -7915,11 +7915,11 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>>         link->detach = &bpf_link__detach_fd;
>>
>>         attach_type = bpf_program__get_expected_attach_type(prog);
>> -       link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
>> +       link_fd = bpf_link_create(prog_fd, target_fd, attach_type, NULL);
>>         if (link_fd < 0) {
>>                 link_fd = -errno;
>>                 free(link);
>> -               pr_warn("program '%s': failed to attach to cgroup: %s\n",
>> +               pr_warn("program '%s': failed to attach to cgroup/netns: %s\n",
>
> I understand the desire to save few lines of code, but it hurts error
> reporting. Now it's cgroup/netns, tomorrow cgroup/netns/lirc/whatever.
> If you want to generalize, let's preserve clarity of error message,
> please.

Ok, that's fair. I could pass the link type bpf_program__attach_fd and
map it to a string.

>
>>                         bpf_program__title(prog, false),
>>                         libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
>>                 return ERR_PTR(link_fd);
>> @@ -7928,6 +7928,18 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>>         return link;
>>  }
>>
>> +struct bpf_link *
>> +bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>> +{
>> +       return bpf_program__attach_fd(prog, cgroup_fd);
>> +}
>> +
>> +struct bpf_link *
>> +bpf_program__attach_netns(struct bpf_program *prog, int netns_fd)
>> +{
>> +       return bpf_program__attach_fd(prog, netns_fd);
>> +}
>> +
>>  struct bpf_link *
>>  bpf_program__attach_iter(struct bpf_program *prog,
>>                          const struct bpf_iter_attach_opts *opts)
>> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
>> index 1e2e399a5f2c..adf6fd9b6fe8 100644
>> --- a/tools/lib/bpf/libbpf.h
>> +++ b/tools/lib/bpf/libbpf.h
>> @@ -253,6 +253,8 @@ LIBBPF_API struct bpf_link *
>>  bpf_program__attach_lsm(struct bpf_program *prog);
>>  LIBBPF_API struct bpf_link *
>>  bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd);
>> +LIBBPF_API struct bpf_link *
>> +bpf_program__attach_netns(struct bpf_program *prog, int netns_fd);
>>
>>  struct bpf_map;
>>
>> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
>> index 381a7342ecfc..7ad21ba1feb6 100644
>> --- a/tools/lib/bpf/libbpf.map
>> +++ b/tools/lib/bpf/libbpf.map
>> @@ -263,4 +263,5 @@ LIBBPF_0.0.9 {
>>                 bpf_link_get_next_id;
>>                 bpf_program__attach_iter;
>>                 perf_buffer__consume;
>> +               bpf_program__attach_netns;
>
> Please keep it alphabetical.

Will do. Not sure how I didn't pick up the convention.

>>  } LIBBPF_0.0.8;
>> --
>> 2.25.4