Re: [PATCH bpf-next v3 1/3] libbpf: Refactor libbpf_probe_bpf_helper

Andrii Nakryiko
2025-01-24T18:44:20Z

On Fri, Jan 24, 2025 at 6:44 AM Tao Chen <chen.dylane@gmail.com> wrote:
>
> Extract the common part as probe_func_comm, which will be used in
> both libbpf_probe_bpf_{helper, kfunc}
>
> Signed-off-by: Tao Chen <chen.dylane@gmail.com>
> ---
> tools/lib/bpf/libbpf_probes.c | 38 ++++++++++++++++++++++++-----------
> 1 file changed, 26 insertions(+), 12 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
> index 9dfbe7750f56..b73345977b4e 100644
> --- a/tools/lib/bpf/libbpf_probes.c
> +++ b/tools/lib/bpf/libbpf_probes.c
> @@ -413,22 +413,20 @@ int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void *opts)
> return libbpf_err(ret);
> }
>
> -int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
> - const void *opts)
> +static int probe_func_comm(enum bpf_prog_type prog_type, struct bpf_insn insn,
> + char *accepted_msgs, size_t msgs_size)
> {
> struct bpf_insn insns[] = {
> - BPF_EMIT_CALL((__u32)helper_id),
> + BPF_EXIT_INSN(),
> BPF_EXIT_INSN(),
> };
> const size_t insn_cnt = ARRAY_SIZE(insns);
> - char buf[4096];
> - int ret;
> + int err;
>
> - if (opts)
> - return libbpf_err(-EINVAL);
> + insns[0] = insn;
>
> /* we can't successfully load all prog types to check for BPF helper
> - * support, so bail out with -EOPNOTSUPP error
> + * and kfunc support, so bail out with -EOPNOTSUPP error
> */
> switch (prog_type) {
> case BPF_PROG_TYPE_TRACING:

there isn't much logic that you will extract here besides this check
whether program type can even be successfully loaded, so I wouldn't
extract probe_func_comm(), but rather extract just the check:

static bool can_probe_prog_type(enum bpf_prog_type prog_type)
{
/* we can't successfully load all prog types to check for BPF
helper/kfunc
* support, so check this early and bail
*/
switch (prog_type) {
...: return false
default:
return true;
}

And just check that can_probe_prog_type() inside
libbpf_probe_bpf_helper and libbpf_probe_bpf_kfunc

pw-bot: cr

> @@ -440,10 +438,26 @@ int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helpe
> break;
> }
>
> - buf[0] = '\0';
> - ret = probe_prog_load(prog_type, insns, insn_cnt, buf, sizeof(buf));
> - if (ret < 0)
> - return libbpf_err(ret);
> + accepted_msgs[0] = '\0';
> + err = probe_prog_load(prog_type, insns, insn_cnt, accepted_msgs, msgs_size);
> + if (err < 0)
> + return libbpf_err(err);
> +
> + return 0;
> +}
> +
> +int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id,
> + const void *opts)
> +{
> + char buf[4096];
> + int ret;
> +
> + if (opts)
> + return libbpf_err(-EINVAL);
> +
> + ret = probe_func_comm(prog_type, BPF_EMIT_CALL((__u32)helper_id), buf, sizeof(buf));
> + if (ret)
> + return ret;
>
> /* If BPF verifier doesn't recognize BPF helper ID (enum bpf_func_id)
> * at all, it will emit something like "invalid func unknown#181".
> --
> 2.43.0
>