Re: [PATCH bpf-next v5 1/3] bpf: Show precise link_type for {uprobe,kprobe}_multi fdinfo

[Tao Chen <chen.dylane@xxxxxxxxx>]

在 2025/6/24 23:46, Andrii Nakryiko 写道:
> On Tue, Jun 24, 2025 at 1:41 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> > 在 2025/6/24 16:16, Jiri Olsa 写道:
> > > On Mon, Jun 23, 2025 at 01:59:18PM -0700, Andrii Nakryiko wrote:
> > > > On Mon, Jun 23, 2025 at 10:56 AM Alexei Starovoitov
> > > > <alexei.starovoitov@xxxxxxxxx> wrote:
> > > > > On Mon, Jun 23, 2025 at 6:44 AM Tao Chen <chen.dylane@xxxxxxxxx> wrote:
> > > > > > Alexei suggested, 'link_type' can be more precise and differentiate
> > > > > > for human in fdinfo. In fact BPF_LINK_TYPE_KPROBE_MULTI includes
> > > > > > kretprobe_multi type, the same as BPF_LINK_TYPE_UPROBE_MULTI, so we
> > > > > > can show it more concretely.
> > > > > >
> > > > > > link_type:      kprobe_multi
> > > > > > link_id:        1
> > > > > > prog_tag:       d2b307e915f0dd37
> > > > > > ...
> > > > > > link_type:      kretprobe_multi
> > > > > > link_id:        2
> > > > > > prog_tag:       ab9ea0545870781d
> > > > > > ...
> > > > > > link_type:      uprobe_multi
> > > > > > link_id:        9
> > > > > > prog_tag:       e729f789e34a8eca
> > > > > > ...
> > > > > > link_type:      uretprobe_multi
> > > > > > link_id:        10
> > > > > > prog_tag:       7db356c03e61a4d4
> > > > > >
> > > > > > Signed-off-by: Tao Chen <chen.dylane@xxxxxxxxx>
> > > > > > ---
> > > > > >    include/linux/trace_events.h | 10 ++++++++++
> > > > > >    kernel/bpf/syscall.c         |  9 ++++++++-
> > > > > >    kernel/trace/bpf_trace.c     | 28 ++++++++++++++++++++++++++++
> > > > > >    3 files changed, 46 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > Change list:
> > > > > >     v4 -> v5:
> > > > > >       - Add patch1 to show precise link_type for
> > > > > >         {uprobe,kprobe}_multi.(Alexei)
> > > > > >       - patch2,3 just remove type field, which will be showed in
> > > > > >         link_type
> > > > > >     v4:
> > > > > >     https://lore.kernel.org/bpf/20250619034257.70520-1-chen.dylane@xxxxxxxxx
> > > > > >
> > > > > >     v3 -> v4:
> > > > > >       - use %pS to print func info.(Alexei)
> > > > > >     v3:
> > > > > >     https://lore.kernel.org/bpf/20250616130233.451439-1-chen.dylane@xxxxxxxxx
> > > > > >
> > > > > >     v2 -> v3:
> > > > > >       - show info in one line for multi events.(Jiri)
> > > > > >     v2:
> > > > > >     https://lore.kernel.org/bpf/20250615150514.418581-1-chen.dylane@xxxxxxxxx
> > > > > >
> > > > > >     v1 -> v2:
> > > > > >       - replace 'func_cnt' with 'uprobe_cnt'.(Andrii)
> > > > > >       - print func name is more readable and security for kprobe_multi.(Alexei)
> > > > > >     v1:
> > > > > >     https://lore.kernel.org/bpf/20250612115556.295103-1-chen.dylane@xxxxxxxxx
> > > > > >
> > > > > > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> > > > > > index fa9cf4292df..951c91babbc 100644
> > > > > > --- a/include/linux/trace_events.h
> > > > > > +++ b/include/linux/trace_events.h
> > > > > > @@ -780,6 +780,8 @@ int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
> > > > > >                               unsigned long *missed);
> > > > > >    int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> > > > > >    int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> > > > > > +void bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
> > > > > > +void bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len);
> > > > > >    #else
> > > > > >    static inline unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
> > > > > >    {
> > > > > > @@ -832,6 +834,14 @@ bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> > > > > >    {
> > > > > >           return -EOPNOTSUPP;
> > > > > >    }
> > > > > > +static inline void
> > > > > > +bpf_kprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
> > > > > > +{
> > > > > > +}
> > > > > > +static inline void
> > > > > > +bpf_uprobe_multi_link_type_show(const struct bpf_link *link, char *link_type, int len)
> > > > > > +{
> > > > > > +}
> > > > > >    #endif
> > > > > >
> > > > > >    enum {
> > > > > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > > > > > index 51ba1a7aa43..43b821b37bc 100644
> > > > > > --- a/kernel/bpf/syscall.c
> > > > > > +++ b/kernel/bpf/syscall.c
> > > > > > @@ -3226,9 +3226,16 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
> > > > > >           const struct bpf_prog *prog = link->prog;
> > > > > >           enum bpf_link_type type = link->type;
> > > > > >           char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
> > > > > > +       char link_type[64] = {};
> > > > > >
> > > > > >           if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) {
> > > > > > -               seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> > > > > > +               if (link->type == BPF_LINK_TYPE_KPROBE_MULTI)
> > > > > > +                       bpf_kprobe_multi_link_type_show(link, link_type, sizeof(link_type));
> > > > > > +               else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI)
> > > > > > +                       bpf_uprobe_multi_link_type_show(link, link_type, sizeof(link_type));
> > > > > > +               else
> > > > > > +                       strscpy(link_type, bpf_link_type_strs[type], sizeof(link_type));
> > > > > > +               seq_printf(m, "link_type:\t%s\n", link_type);
> > > > >
> > > > > New callbacks just to print a string?
> > > > > Let's find a different way.
> > > > >
> > > > > How about moving 'flags' from bpf_[ku]probe_multi_link into bpf_link ?
> > > > > (There is a 7 byte hole there anyway)
> > > > > and checking flags inline.
> > > > >
> > > > > Jiri, Andrii,
> > > > >
> > > > > better ideas?
> > > >
> > > > We can just remember original attr->link_create.attach_type in
> > > > bpf_link itself, and then have a small helper that will accept link
> > > > type and attach type, and fill out link type representation based on
> > > > those two. Internally we can do the special-casing of  uprobe vs
> > > > uretprobe and kprobe vs kretprobe transparently to all the other code.
> > > > And use that here in show_fdinfo
> > >
> > > but you'd still need the flags, no? to find out if it's return probe
> > >
> > > I tried what Alexei suggested and it seems ok and simple enough
> > >
> > > jirka
> > >
> > >
> > > ---
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 5dd556e89cce..287c956cdbd2 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -1702,6 +1702,7 @@ struct bpf_link {
> > >         * link's semantics is determined by target attach hook
> > >         */
> > >        bool sleepable;
> > > +     u32 flags;
> > >        /* rcu is used before freeing, work can be used to schedule that
> > >         * RCU-based freeing before that, so they never overlap
> > >         */
> > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > > index 56500381c28a..f1d9ee9717a1 100644
> > > --- a/kernel/bpf/syscall.c
> > > +++ b/kernel/bpf/syscall.c
> > > @@ -3228,7 +3228,14 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
> > >        char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
> > >
> > >        if (type < ARRAY_SIZE(bpf_link_type_strs) && bpf_link_type_strs[type]) {
> > > -             seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> > > +             if (link->type == BPF_LINK_TYPE_KPROBE_MULTI)
> > > +                     seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_KPROBE_MULTI_RETURN ?
> > > +                                "kretprobe_multi" : "kprobe_multi");
> > > +             else if (link->type == BPF_LINK_TYPE_UPROBE_MULTI)
> > > +                     seq_printf(m, "link_type:\t%s\n", link->flags == BPF_F_UPROBE_MULTI_RETURN ?
> > > +                                "uretprobe_multi" : "uprobe_multi");
> > > +             else
> > > +                     seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> > >        } else {
> > >                WARN_ONCE(1, "missing BPF_LINK_TYPE(...) for link type %u\n", type);
> > >                seq_printf(m, "link_type:\t<%u>\n", type);
> > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > > index 0a06ea6638fe..81d7a4e5ae15 100644
> > > --- a/kernel/trace/bpf_trace.c
> > > +++ b/kernel/trace/bpf_trace.c
> > > @@ -2466,7 +2466,6 @@ struct bpf_kprobe_multi_link {
> > >        u32 cnt;
> > >        u32 mods_cnt;
> > >        struct module **mods;
> > > -     u32 flags;
> > >    };
> > >
> > >    struct bpf_kprobe_multi_run_ctx {
> > > @@ -2586,7 +2585,7 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
> > >
> > >        kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
> > >        info->kprobe_multi.count = kmulti_link->cnt;
> > > -     info->kprobe_multi.flags = kmulti_link->flags;
> > > +     info->kprobe_multi.flags = kmulti_link->link.flags;
> > >        info->kprobe_multi.missed = kmulti_link->fp.nmissed;
> > >
> > >        if (!uaddrs)
> > > @@ -2976,7 +2975,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> > >        link->addrs = addrs;
> > >        link->cookies = cookies;
> > >        link->cnt = cnt;
> > > -     link->flags = flags;
> > > +     link->link.flags = flags;
> > >
> > >        if (cookies) {
> > >                /*
> > > @@ -3045,7 +3044,6 @@ struct bpf_uprobe_multi_link {
> > >        struct path path;
> > >        struct bpf_link link;
> > >        u32 cnt;
> > > -     u32 flags;
> > >        struct bpf_uprobe *uprobes;
> > >        struct task_struct *task;
> > >    };
> > > @@ -3109,7 +3107,7 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
> > >
> > >        umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
> > >        info->uprobe_multi.count = umulti_link->cnt;
> > > -     info->uprobe_multi.flags = umulti_link->flags;
> > > +     info->uprobe_multi.flags = umulti_link->link.flags;
> > >        info->uprobe_multi.pid = umulti_link->task ?
> > >                                 task_pid_nr_ns(umulti_link->task, task_active_pid_ns(current)) : 0;
> > >
> > > @@ -3369,7 +3367,7 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> > >        link->uprobes = uprobes;
> > >        link->path = path;
> > >        link->task = task;
> > > -     link->flags = flags;
> > > +     link->link.flags = flags;
> > >
> > >        bpf_link_init(&link->link, BPF_LINK_TYPE_UPROBE_MULTI,
> > >                      &bpf_uprobe_multi_link_lops, prog);
> >
> > Hi, Jiri, Andrii,
> >
> > Jiri's patch looks more simple, and i see other struct xx_links wrap
> > bpf_link, which have attach_type field like:
> > struct sockmap_link {
> >           struct bpf_link link;
> >           struct bpf_map *map;
> >           enum bpf_attach_type attach_type;
> > };
> > If we create attach_type filed in bpf_link, maybe these struct xx_link
> > should also be modified. BTW, as Jiri said, we still can not find return
> > probe type from attach_type.
>
> You are right, I somehow was under impression that ret vs non-retprobe
> comes from attach type as well.
>
> Ok, moving flags into common bpf_link struct sounds good to me. I'd
> still move attach_type into bpf_link, together with flags, for
> generality (and update all those links that already include
> attach_type as you mentioned). We can make it a single-byte field to
> not increase bpf_link size unnecessarily (by using bitfield size).

Well，can we complete this in two steps?

1. Create a common field in bpf_link used for flags or attach_type, and 
realise the precise link_type feature as Jiri and Alexei said, the 
review of this part has been revised almost completely.

2. Move the attach_type from struct bpf_xx_link into bpf_link, this will 
involve a lot of changes, i will send a separate patchset to finish it.

> > --
> > Best Regards
> > Tao Chen


--
Best Regards
Tao Chen