Message-ID: <1621611c-8cf1-4281-986f-cfd8cc0e70f0@kernel.org>
Date: Mon, 19 May 2025 12:04:55 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>,
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next/net v3 4/5] selftests/bpf: Add mptcp_subflow
 bpf_iter subtest

Hi Martin,

On 17/05/2025 00:48, Martin KaFai Lau wrote:
> On 3/20/25 10:48 AM, Matthieu Baerts (NGI0) wrote:
>> From: Geliang Tang <tanggeliang@...inos.cn>
>>
>> This patch adds a "cgroup/getsockopt" program "iters_subflow" to test the
>> newly added mptcp_subflow bpf_iter.
>>
>> Export mptcp_subflow helpers bpf_iter_mptcp_subflow_new/_next/_destroy
>> and other helpers into bpf_experimental.h.
>>
>> Use bpf_for_each() to walk the subflow list of an msk. From there,
>> future MPTCP-specific kfunc can be called in the loop. Because they are
>> not there yet, this test doesn't do anything very "useful" for the
>> moment, but it focuses on validating the 'bpf_iter' part and the basic
>> MPTCP kfunc. That's why it simply adds all subflow ids to local variable
>> local_ids to make sure all subflows have been seen, then invoke
>> mptcp_subflow_tcp_sock() in the loop to pick the subflow context.
>>
>> Out of the loop, use bpf_mptcp_subflow_ctx() to get the subflow context
>> of the picked subflow context and do some verifications. Finally, assign
>> local_ids to global variable ids so that the application can obtain this
>> value.
>>
>> A related subtest called test_iters_subflow is added to load and verify
>> the newly added mptcp_subflow type bpf_iter example in test_mptcp. The
>> endpoint_init() helper is used to add 3 new subflow endpoints. Then one
>> byte of message is sent to trigger the creation of new subflows.
>> getsockopt() is invoked once the subflows have been created to trigger
>> the "cgroup/getsockopt" test program "iters_subflow". skel->bss->ids is
>> then checked to make sure it equals 10, the sum of each subflow ID: we
>> should have 4 subflows: 1 + 2 + 3 + 4 = 10. If that's the case, the
>> bpf_iter loop did the job as expected.

(...)

>> diff --git a/tools/testing/selftests/bpf/progs/mptcp_bpf_iters.c b/
>> tools/testing/selftests/bpf/progs/mptcp_bpf_iters.c
>> new file mode 100644
>> index
>> 0000000000000000000000000000000000000000..a1d8f9b20259a9cbdc46d58e0d18157564fa5acd
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/mptcp_bpf_iters.c
>> @@ -0,0 +1,59 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2024, Kylin Software */
>> +
>> +/* vmlinux.h, bpf_helpers.h and other 'define' */
>> +#include "bpf_tracing_net.h"
>> +#include "mptcp_bpf.h"
>> +
>> +char _license[] SEC("license") = "GPL";
>> +int ids;
>> +
>> +#ifndef TCP_IS_MPTCP
>> +#define TCP_IS_MPTCP        43    /* Is MPTCP being used? */
>> +#endif
>> +
>> +SEC("cgroup/getsockopt")
>> +int iters_subflow(struct bpf_sockopt *ctx)
>> +{
>> +    struct mptcp_subflow_context *subflow;
>> +    struct bpf_sock *sk = ctx->sk;
>> +    struct sock *ssk = NULL;
>> +    struct mptcp_sock *msk;
>> +    int local_ids = 0;
>> +
>> +    if (ctx->level != SOL_TCP || ctx->optname != TCP_IS_MPTCP)
>> +        return 1;
>> +
>> +    msk = bpf_core_cast(sk, struct mptcp_sock);
>> +    if (!msk || msk->pm.server_side || !msk->pm.subflows)
>> +        return 1;
>> +
>> +    bpf_for_each(mptcp_subflow, subflow, (struct sock *)sk) {
>> +        /* Here MPTCP-specific packet scheduler kfunc can be called:
>> +         * this test is not doing anything really useful, only to
> 
> Lets fold the bpf_iter_mptcp_subflow addition into the future
> "mptcp_sched_ops" set (the github link that you mentioned in patch 2).
> Post them as one set to have a more practical example.

Thank you for this suggestion. We can delay that if needed.

Note that we have two struct_ops in preparation: mptcp_sched_ops and
mptcp_pm_ops. We don't know which one will be ready first. They are both
"blocked" by internal API modifications we would like to do to ease the
maintenance later before "exposing" such API's via BPF. That's why we
suggested to upstream this common part first as it is ready. But we can
of course wait if you prefer.

>> +         * verify the iteration works.
>> +         */
>> +
>> +        local_ids += subflow->subflow_id;
>> +
>> +        /* only to check the following helper works */
>> +        ssk = mptcp_subflow_tcp_sock(subflow);
>> +    }
>> +
>> +    if (!ssk)
>> +        goto out;
>> +
>> +    /* assert: if not OK, something wrong on the kernel side */
>> +    if (ssk->sk_dport != ((struct sock *)msk)->sk_dport)
>> +        goto out;
>> +
>> +    /* only to check the following kfunc works */
>> +    subflow = bpf_mptcp_subflow_ctx(ssk);
> 
> bpf_core_cast should be as good instead of adding a new
> bpf_mptcp_subflow_ctx() kfunc, so patch 1 should not be needed.

OK, indeed, in this series we don't need it. We will need it later to
modify some fields from the "subflow" structure directly. We can do the
modification or drop this test when the new struct_ops will be ready.

>> +    if (!subflow || subflow->token != msk->token)
>> +        goto out;
>> +
>> +    ids = local_ids;
>> +
>> +out:
>> +    return 1;
>> +}
>>
> 
> 

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

Powered by blists - more mailing lists