Re: BPF maps don't work without CONFIG_TRACING/CONFIG_FTRACE

["Toke Høiland-Jørgensen" <toke@kernel.org>]

Michael Zimmermann <sigmaepsilon92@gmail.com> writes:

> On Thu, May 12, 2022 at 5:21 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
>>
>> On Mon, May 9, 2022 at 10:12 PM Michael Zimmermann
>> <sigmaepsilon92@gmail.com> wrote:
>> >
>> > Thank you for your answer.
>> > What I'm ultimately trying to do is: Use aya-rs to watch egress on a
>> > network interface and notify userspace through a map (for certain IPs
>> > only).
>> >
>> > In my actual use case, the userspace is supposed to do more complex
>> > stuff but for testing I simply logged the receival of a message
>> > through the BPF map on the console. And that is what I expect to
>> > happen and which does happen as long as CONFIG_TRACING/CONFIG_FTRACE
>> > are active. If not, I simply never receive any messages on any map.
>> >
>> > I've also tried this using an XDP program which sends a message every
>> > time it sees a packet. And while the program seemed to be
>> > working(since it did block certain traffic), I never saw any data in
>> > the map when those configs were disabled.
>> >
>> > Also, I'm giving you two configs(tracing and ftrace) since the other
>> > one seems to get y-selected automatically if one of them is active.
>>
>> Please don't top post, reply inline instead.
> Sorry for that, GMail does that by default and even hides that it's
> quoting at all.
>
>>
>> I don't think we have enough to investigate here, even "receive any
>> messages on any map" is so ambiguous that it's hard to even guess what
>> you are really trying to do. BPF maps are not sending/receiving
>> messages. So please provide some pieces of code and what you are doing
>> to check. CONFIG_TRACING and CONFIG_FTRACE shouldn't have any effect
>> on functioning of BPF maps, so it's most probably that you are doing
>> something besides BPF map update/lookup, but you don't provide enough
>> information to check anything.
>
> An aya project I tested where I don't receive any events:
> https://github.com/aya-rs/book/tree/6b52a6fac5fa3e5a1165f98591b2eaff9692048a/examples/myapp-03

It's using a PERF_EVENT_ARRAY map to send events to userspace. This
requires CONFIG_BPF_EVENTS to work, which depends on CONFIG_PERF_EVENTS.
Not sure if this depends on CONFIG_TRACING specifically, but maybe you
disabled PERF_EVENTS as well?

-Toke