Re: [PATCH bpf-next v4 1/3] libbpf: add support to set kprobe/uprobe attach mode

[Andrii Nakryiko]

On Sun, Mar 5, 2023 at 10:48 PM <menglong8.dong@xxxxxxxxx> wrote:
>
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
>
> By default, libbpf will attach the kprobe/uprobe BPF program in the
> latest mode that supported by kernel. In this patch, we add the support
> to let users manually attach kprobe/uprobe in legacy or perf mode.
>
> There are 3 mode that supported by the kernel to attach kprobe/uprobe:
>
>   LEGACY: create perf event in legacy way and don't use bpf_link
>   PERF: create perf event with perf_event_open() and don't use bpf_link
>   LINK: create perf event with perf_event_open() and use bpf_link
>
> Users now can manually choose the mode with
> bpf_program__attach_uprobe_opts()/bpf_program__attach_kprobe_opts().
>
> Link: https://lore.kernel.org/bpf/20230113093427.1666466-1-imagedong@xxxxxxxxxxx/
> Reviewed-by: Biao Jiang <benbjiang@xxxxxxxxxxx>
> Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
> ---

I fixed few small issues I pointed out below and applied to bpf-next. Thanks!

> v4:
> - rename eBPF to BPF in the doc
> - use OPTS_GET() to get the value of 'force_ioctl_attach'
> - error out on attach mode is not supported
> v2:
> - rename no_link to force_ioctl_attach
> - rename probe_mode to probe_attach_mode
> - add more doc for probe_attach_mode
> - return -ENOTSUP when necessray in bpf_program__attach_uprobe_opts and
>   bpf_program__attach_kprobe_opts
> ---
>  tools/lib/bpf/libbpf.c | 47 +++++++++++++++++++++++++++++++++++++++++-
>  tools/lib/bpf/libbpf.h | 31 +++++++++++++++++++++++++---
>  2 files changed, 74 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index dacaae31b76a..77df4d275d22 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9747,7 +9747,8 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
>         link->link.dealloc = &bpf_link_perf_dealloc;
>         link->perf_event_fd = pfd;
>
> -       if (kernel_supports(prog->obj, FEAT_PERF_LINK)) {
> +       if (kernel_supports(prog->obj, FEAT_PERF_LINK) && !OPTS_GET(opts, force_ioctl_attach,
> +                                                                   false)) {

too ugly, I added local variable for OPTS_GET() result

>                 DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts,
>                         .perf_event.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0));
>
> @@ -10106,6 +10107,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>                                 const struct bpf_kprobe_opts *opts)
>  {
>         DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
> +       enum probe_attach_mode attach_mode;
>         char errmsg[STRERR_BUFSIZE];
>         char *legacy_probe = NULL;
>         struct bpf_link *link;
> @@ -10116,11 +10118,32 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>         if (!OPTS_VALID(opts, bpf_kprobe_opts))
>                 return libbpf_err_ptr(-EINVAL);
>
> +       attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
>         retprobe = OPTS_GET(opts, retprobe, false);
>         offset = OPTS_GET(opts, offset, 0);
>         pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
>
>         legacy = determine_kprobe_perf_type() < 0;
> +       switch (attach_mode) {
> +       case PROBE_ATTACH_MODE_LEGACY:
> +               legacy = true;
> +               pe_opts.force_ioctl_attach = true;
> +               break;
> +       case PROBE_ATTACH_MODE_PERF:
> +               if (legacy)
> +                       return libbpf_err_ptr(-ENOTSUP);
> +               pe_opts.force_ioctl_attach = true;
> +               break;
> +       case PROBE_ATTACH_MODE_LINK:
> +               if (legacy || !kernel_supports(prog->obj, FEAT_PERF_LINK))
> +                       return libbpf_err_ptr(-ENOTSUP);
> +               break;
> +       case PROBE_ATTACH_MODE_DEFAULT:
> +               break;
> +       default:
> +               return libbpf_err_ptr(-ENOTSUP);

this should have been -EINVAL, I changed it; same for another instance below

> +       }
> +
>         if (!legacy) {
>                 pfd = perf_event_open_probe(false /* uprobe */, retprobe,
>                                             func_name, offset,

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