Re: [RFC PATCH bpf-next 3/8] bpftool: Show probed function in kprobe_multi link info

From: Yafang Shao <laoar.shao@gmail.com>
To: Quentin Monnet <quentin@isovalent.com>
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
	 andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
	yhs@fb.com,  kpsingh@kernel.org, sdf@google.com,
	haoluo@google.com, jolsa@kernel.org,  bpf@vger.kernel.org
Subject: Re: [RFC PATCH bpf-next 3/8] bpftool: Show probed function in kprobe_multi link info
Date: Wed, 31 May 2023 11:16:20 +0800	[thread overview]
Message-ID: <CALOAHbAJscwrQthOSaYvqkmB2tOkkO2txXbTvZ9WvaBpAa39XA@mail.gmail.com> (raw)
In-Reply-To: <313a276f-aab9-42ed-e835-32261c25bb39@isovalent.com>

On Tue, May 30, 2023 at 7:16 PM Quentin Monnet <quentin@isovalent.com> wrote:
>
> 2023-05-28 14:20 UTC+0000 ~ Yafang Shao <laoar.shao@gmail.com>
> > Show the already expose kprobe_multi link info in bpftool. The result as
> > follows,
> >
> > $ bpftool link show
> > 2: kprobe_multi  prog 11
> >         func_cnt 4  addrs ffffffffaad475c0 ffffffffaad47600
> >                           ffffffffaad47640 ffffffffaad47680
> >         pids trace(10936)
> >
> > $ bpftool link show -j
> > [{"id":1,"type":"perf_event","prog_id":5,"bpf_cookie":0,"pids":[{"pid":10658,"comm":"trace"}]},{"id":2,"type":"kprobe_multi","prog_id":11,"func_cnt":4,"addrs":[18446744072280634816,18446744072280634880,18446744072280634944,18446744072280635008],"pids":[{"pid":10936,"comm":"trace"}]},{"id":120,"type":"iter","prog_id":266,"target_name":"bpf_map"},{"id":121,"type":"iter","prog_id":267,"target_name":"bpf_prog"}]
> >
> > $ bpftool link show  | grep -A 1 "func_cnt" | \
> >   awk '{if (NR == 1) {print $4; print $5;} else {print $1; print $2} }' | \
> >   awk '{"grep " $1 " /proc/kallsyms" | getline f; print f;}'
> > ffffffffaad475c0 T schedule_timeout_interruptible
> > ffffffffaad47600 T schedule_timeout_killable
> > ffffffffaad47640 T schedule_timeout_uninterruptible
> > ffffffffaad47680 T schedule_timeout_idle
>
> Looks nice, thank you!
>
> The address is a useful addition, but I feel like most of the time, this
> is the actual function name that we'd like to see. We could maybe print
> it directly in bpftool, what do you think? We already parse
> /proc/kallsyms elsewhere (to get the address of __bpf_call_base()). If
> we can parse the file only once for all func_cnt function, the overhead
> is maybe acceptable?
>

Thanks for your suggestion. Will change it.

> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  tools/bpf/bpftool/link.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 50 insertions(+)
> >
> > diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> > index 2d78607..76f1bb2 100644
> > --- a/tools/bpf/bpftool/link.c
> > +++ b/tools/bpf/bpftool/link.c
> > @@ -218,6 +218,20 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
> >               jsonw_uint_field(json_wtr, "map_id",
> >                                info->struct_ops.map_id);
> >               break;
> > +     case BPF_LINK_TYPE_KPROBE_MULTI:
> > +             const __u64 *addrs;
> > +             __u32 i;
> > +
> > +             jsonw_uint_field(json_wtr, "func_cnt", info->kprobe_multi.count);
> > +             if (!info->kprobe_multi.count)
> > +                     break;
>
> I'd as well avoid having conditional entries in the JSON output. Let's
> just keep 0 and empty array in this case?
>

Will do it.

> > +             jsonw_name(json_wtr, "addrs");
> > +             jsonw_start_array(json_wtr);
> > +             addrs = (const __u64 *)u64_to_ptr(info->kprobe_multi.addrs);
> > +             for (i = 0; i < info->kprobe_multi.count; i++)
> > +                     jsonw_lluint(json_wtr, addrs[i]);
> > +             jsonw_end_array(json_wtr);
> > +             break;
> >       default:
> >               break;
> >       }
> > @@ -396,6 +410,24 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
> >       case BPF_LINK_TYPE_NETFILTER:
> >               netfilter_dump_plain(info);
> >               break;
> > +     case BPF_LINK_TYPE_KPROBE_MULTI:
> > +             __u32 indent, cnt, i;
> > +             const __u64 *addrs;
> > +
> > +             cnt = info->kprobe_multi.count;
> > +             if (!cnt)
> > +                     break;
> > +             printf("\n\tfunc_cnt %d  addrs", cnt);
> > +             for (i = 0; cnt; i++)
> > +                     cnt /= 10;
> > +             indent = strlen("func_cnt ") + i + strlen("  addrs");
> > +             addrs = (const __u64 *)u64_to_ptr(info->kprobe_multi.addrs);
> > +             for (i = 0; i < info->kprobe_multi.count; i++) {
> > +                     if (i && !(i & 0x1))
> > +                             printf("\n\t%*s", indent, "");
> > +                     printf(" %0*llx", 16, addrs[i]);
> > +             }
> > +             break;
> >       default:
> >               break;
> >       }
> > @@ -417,7 +449,9 @@ static int do_show_link(int fd)
> >  {
> >       struct bpf_link_info info;
> >       __u32 len = sizeof(info);
> > +     __u64 *addrs = NULL;
> >       char buf[256];
> > +     int count;
> >       int err;
> >
> >       memset(&info, 0, sizeof(info));
> > @@ -441,12 +475,28 @@ static int do_show_link(int fd)
> >               info.iter.target_name_len = sizeof(buf);
> >               goto again;
> >       }
> > +     if (info.type == BPF_LINK_TYPE_KPROBE_MULTI &&
> > +         !info.kprobe_multi.addrs) {
> > +             count = info.kprobe_multi.count;
> > +             if (count) {
> > +                     addrs = malloc(count * sizeof(__u64));
>
> Nit: calloc() instead?

Good point. Will do it.

>
> > +                     if (!addrs) {
> > +                             p_err("mem alloc failed");
> > +                             close(fd);
> > +                             return -1;
> > +                     }
> > +                     info.kprobe_multi.addrs = (unsigned long)addrs;
> > +                     goto again;
> > +             }
> > +     }
> >
> >       if (json_output)
> >               show_link_close_json(fd, &info);
> >       else
> >               show_link_close_plain(fd, &info);
> >
> > +     if (addrs)
> > +             free(addrs);
> >       close(fd);
> >       return 0;
> >  }
>
> The other bpftool patch (perf_event link) looks good to me.
>

Thanks for your review.

-- 
Regards
Yafang