[PATCH bpf-next v2 0/2] Allow BPF TCP CCs to write app_limited

[PATCH bpf-next v2 0/2] Allow BPF TCP CCs to write app_limited

[Yixin Shen]

This series allow BPF TCP CCs to write app_limited of struct
tcp_sock. A built-in CC or one from a kernel module is already
able to write to app_limited of struct tcp_sock. Until now,
a BPF CC doesn't have write access to this member of struct
tcp_sock.

v2:
 - Merge the test of writing app_limited into the test of
   writing sk_pacing. (Martin KaFai Lau)
 
Yixin Shen (2):
  bpf: allow a TCP CC to write app_limited
  selftests/bpf: test a BPF CC writing app_limited

 net/ipv4/bpf_tcp_ca.c                               |  3 +++
 .../selftests/bpf/progs/tcp_ca_write_sk_pacing.c    | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

-- 
2.25.1

[PATCH bpf-next v2 1/2] bpf: allow a TCP CC to write app_limited

[Yixin Shen]

A CC that implements tcp_congestion_ops.cong_control() should be able to
write app_limited. A built-in CC or one from a kernel module is already
able to write to this member of struct tcp_sock.
For a BPF program, write access has not been allowed, yet.

Signed-off-by: Yixin Shen <bobankhshen@gmail.com>
---
 net/ipv4/bpf_tcp_ca.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index e8b27826283e..ea21c96c03aa 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -113,6 +113,9 @@ static int bpf_tcp_ca_btf_struct_access(struct bpf_verifier_log *log,
 	case offsetof(struct tcp_sock, ecn_flags):
 		end = offsetofend(struct tcp_sock, ecn_flags);
 		break;
+	case offsetof(struct tcp_sock, app_limited):
+		end = offsetofend(struct tcp_sock, app_limited);
+		break;
 	default:
 		bpf_log(log, "no write support to tcp_sock at off %d\n", off);
 		return -EACCES;
-- 
2.25.1

[PATCH bpf-next v2 2/2] selftests/bpf: test a BPF CC writing app_limited

[Yixin Shen]

Test whether a TCP CC implemented in BPF is allowed to write
app_limited in struct tcp_sock. This is already allowed for
the built-in TCP CC.

Signed-off-by: Yixin Shen <bobankhshen@gmail.com>
---
 .../selftests/bpf/progs/tcp_ca_write_sk_pacing.c    | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c b/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c
index 43447704cf0e..0724a79cec78 100644
--- a/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c
+++ b/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c
@@ -16,6 +16,16 @@ static inline struct tcp_sock *tcp_sk(const struct sock *sk)
 	return (struct tcp_sock *)sk;
 }
 
+static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
+{
+	return tp->sacked_out + tp->lost_out;
+}
+
+static inline unsigned int tcp_packets_in_flight(const struct tcp_sock *tp)
+{
+	return tp->packets_out - tcp_left_out(tp) + tp->retrans_out;
+}
+
 SEC("struct_ops/write_sk_pacing_init")
 void BPF_PROG(write_sk_pacing_init, struct sock *sk)
 {
@@ -31,11 +41,12 @@ SEC("struct_ops/write_sk_pacing_cong_control")
 void BPF_PROG(write_sk_pacing_cong_control, struct sock *sk,
 	      const struct rate_sample *rs)
 {
-	const struct tcp_sock *tp = tcp_sk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
 	unsigned long rate =
 		((tp->snd_cwnd * tp->mss_cache * USEC_PER_SEC) << 3) /
 		(tp->srtt_us ?: 1U << 3);
 	sk->sk_pacing_rate = min(rate, sk->sk_max_pacing_rate);
+	tp->app_limited = (tp->delivered + tcp_packets_in_flight(tp)) ?: 1;
 }
 
 SEC("struct_ops/write_sk_pacing_ssthresh")
-- 
2.25.1

Re: [PATCH bpf-next v2 0/2] Allow BPF TCP CCs to write app_limited

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Wed, 29 Mar 2023 07:35:56 +0000 you wrote:
> This series allow BPF TCP CCs to write app_limited of struct
> tcp_sock. A built-in CC or one from a kernel module is already
> able to write to app_limited of struct tcp_sock. Until now,
> a BPF CC doesn't have write access to this member of struct
> tcp_sock.
> 
> v2:
>  - Merge the test of writing app_limited into the test of
>    writing sk_pacing. (Martin KaFai Lau)
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/2] bpf: allow a TCP CC to write app_limited
    https://git.kernel.org/bpf/bpf-next/c/562dc56a8898
  - [bpf-next,v2,2/2] selftests/bpf: test a BPF CC writing app_limited
    https://git.kernel.org/bpf/bpf-next/c/4239561b69fe

You are awesome, thank you!
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