[PATCH mptcp-next v2 1/4] bpf: Add mptcp_subflow bpf_iter

[Geliang Tang <geliang@xxxxxxxxxx>]

From: Geliang Tang <tanggeliang@xxxxxxxxxx>

It's necessary to traverse all subflows on the conn_list of an MPTCP
socket and then call kfunc to modify the fields of each subflow. In
kernel space, mptcp_for_each_subflow() helper is used for this:

	mptcp_for_each_subflow(msk, subflow)
		kfunc(subflow);

But in the MPTCP BPF program, this has not yet been implemented. As
Martin suggested recently, this conn_list walking + modify-by-kfunc
usage fits the bpf_iter use case. So this patch adds a new bpf_iter
type named "mptcp_subflow" to do this and implements its helpers
bpf_iter_mptcp_subflow_new()/_next()/_destroy().

Then bpf_for_each() for mptcp_subflow can be used in BPF program like
this:

	bpf_rcu_read_lock();
	bpf_for_each(mptcp_subflow, subflow, msk)
		kfunc(subflow);
	bpf_rcu_read_unlock();

Suggested-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Signed-off-by: Geliang Tang <tanggeliang@xxxxxxxxxx>
---
 net/mptcp/bpf.c      | 51 ++++++++++++++++++++++++++++++++++++++++++++
 net/mptcp/protocol.h |  6 ++++++
 2 files changed, 57 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 9672a70c24b0..799264119891 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -204,10 +204,59 @@ static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
 	.set   = &bpf_mptcp_fmodret_ids,
 };
 
+struct bpf_iter__mptcp_subflow {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct mptcp_sock *, msk);
+	__bpf_md_ptr(struct list_head *, pos);
+};
+
+struct bpf_iter_mptcp_subflow {
+	__u64 __opaque[2];
+} __attribute__((aligned(8)));
+
+struct bpf_iter_mptcp_subflow_kern {
+	struct mptcp_sock *msk;
+	struct list_head *pos;
+} __attribute__((aligned(8)));
+
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
 		  "kfuncs which will be used in BPF programs");
 
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc int bpf_iter_mptcp_subflow_new(struct bpf_iter_mptcp_subflow *it,
+					   struct mptcp_sock *msk)
+{
+	struct bpf_iter_mptcp_subflow_kern *kit = (void *)it;
+
+	if (!msk)
+		return -EINVAL;
+
+	kit->msk = msk;
+	kit->pos = &msk->conn_list;
+	return 0;
+}
+
+__bpf_kfunc struct mptcp_subflow_context *
+bpf_iter_mptcp_subflow_next(struct bpf_iter_mptcp_subflow *it)
+{
+	struct bpf_iter_mptcp_subflow_kern *kit = (void *)it;
+	struct mptcp_subflow_context *subflow;
+	struct mptcp_sock *msk = kit->msk;
+
+	subflow = list_entry((kit->pos)->next, struct mptcp_subflow_context, node);
+	if (!msk || list_entry_is_head(subflow, &msk->conn_list, node))
+		return NULL;
+
+	kit->pos = &subflow->node;
+	return subflow;
+}
+
+__bpf_kfunc void bpf_iter_mptcp_subflow_destroy(struct bpf_iter_mptcp_subflow *it)
+{
+}
+
 __bpf_kfunc struct mptcp_subflow_context *
 bpf_mptcp_subflow_ctx_by_pos(const struct mptcp_sched_data *data, unsigned int pos)
 {
@@ -221,6 +270,8 @@ __bpf_kfunc bool bpf_mptcp_subflow_queues_empty(struct sock *sk)
 	return tcp_rtx_queue_empty(sk);
 }
 
+__bpf_kfunc_end_defs();
+
 __diag_pop();
 
 BTF_KFUNCS_START(bpf_mptcp_sched_kfunc_ids)
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index d25d2dac88a5..b3f5254e3c0d 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -715,6 +715,12 @@ void mptcp_subflow_queue_clean(struct sock *sk, struct sock *ssk);
 void mptcp_sock_graft(struct sock *sk, struct socket *parent);
 u64 mptcp_wnd_end(const struct mptcp_sock *msk);
 void mptcp_set_timeout(struct sock *sk);
+struct bpf_iter_mptcp_subflow;
+int bpf_iter_mptcp_subflow_new(struct bpf_iter_mptcp_subflow *it,
+			       struct mptcp_sock *msk);
+struct mptcp_subflow_context *
+bpf_iter_mptcp_subflow_next(struct bpf_iter_mptcp_subflow *it);
+void bpf_iter_mptcp_subflow_destroy(struct bpf_iter_mptcp_subflow *it);
 bool bpf_mptcp_subflow_queues_empty(struct sock *sk);
 struct mptcp_subflow_context *
 bpf_mptcp_subflow_ctx_by_pos(const struct mptcp_sched_data *data, unsigned int pos);
-- 
2.43.0