Le 15 mars 2022 18:33:02 GMT+00:00, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> a écrit :
>On Sat, Mar 12, 2022 at 2:59 PM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote:
>>
>> On Fri, 11 Mar 2022 at 22:25, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>> >
>> > On Wed, Mar 9, 2022 at 8:33 AM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote:
>> > >
>> > > Commit 82e6b1eee6a8 ("bpf: Allow to specify user-provided bpf_cookie for
>> > > BPF perf links") introduced the concept of user specified bpf_cookie,
>> > > which could be accessed by BPF programs using bpf_get_attach_cookie().
>> > > For troubleshooting purposes it is convenient to expose bpf_cookie via
>> > > bpftool as well, so there is no need to meddle with the target BPF
>> > > program itself.
>> > >
>> > > Implemented using the pid iterator BPF program to actually fetch
>> > > bpf_cookies, which allows constraining code changes only to bpftool.
>> > >
>> > > $ bpftool link
>> > > 1: type 7 prog 5
>> > > bpf_cookie 123
>> > > pids bootstrap(81)
>> > >
>> > > Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx>
>> > > Acked-by: Yonghong Song <yhs@xxxxxx>
>> > > ---
>> >
>> > Quentin, any opinion on this feature? The implementation seems
>> > straightforward enough. We'll need to not forget to expand the support
>> > to other types that support bpf_cookies (and multi-attach kprobes and
>> > fentries will be problematic, potentially), but this might be useful
>> > for debugging purposes.
>>
>> No strong opinion. I'm generally in favour of adding more useful info
>> to bpftool's output; I've not found myself in need for the bpf_cookie
>> so far, but if it's helpful for debugging, then it makes sense to me
>> that bpftool be the tool to provide the info. The change looks clean
>
>Can I get your ack for this change, then?
Acked-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
>
>> indeed. Agreed also that this will require us to think of updating
>> bpftool when new types gain support for the cookies. What would be the
>> problem with multi-attach, the kprobes/fentries would have several
>> cookies?
>
>Yes, multi-attach links will have one cookie for each attach target,
>so there will be, in general, a multitude of cookie values.
OK thank you
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