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bpf: tcp: Add kfunc to adjust sk->sk_rcvlowat.

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bpf_tcp_ops.{enqueue,dequeue}_rcvq() were added to parse skb and
adjust sk->sk_rcvlowat dynamically to suppress unnecessary wakeups.

Let's add a new kfunc to set sk->sk_rcvlowat.

Negative values are clamped to INT_MAX, consistent with SO_RCVLOWAT.

For enqueue_rcvq(), wakeup is set to false because:

  * tcp_data_ready() is always called after the hooks in
    tcp_queue_rcv() and tcp_ofo_queue().

  * when tcp_fastopen_add_skb() is called for TFO SYN, the socket is
    not yet accept()ed, and when called for TFO SYN+ACK, the socket
    is woken up by sk->sk_state_change() anyway.

For dequeue_rcvq(), wakeup is set to true because tcp_data_ready()
is not called in that path.

An alternative would be to support bpf_setsockopt() for these
hooks.

However, that approach involves excessive conditionals and an
unnecessary memcpy(), costs we do not want to pay for every skb
in the TCP fast path.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Clément Léger <cleger@meta.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20261008031604.256498-10-kuniyu@google.com
This commit is contained in:
Kuniyuki Iwashima 2026-10-08 03:15:29 +00:00 committed by Alexei Starovoitov
parent d65dc83603
commit 5f549c1e49
No known key found for this signature in database
1 changed files with 46 additions and 0 deletions
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46
net/ipv4/bpf_tcp_ops.c
View File

@ -361,12 +361,31 @@ __bpf_kfunc int bpf_tcp_ops_set_flags(struct tcp_sock *tp, u32 enable, u32 disab
return 0;
}
__bpf_kfunc int bpf_tcp_ops_set_rcvlowat(struct sock *sk, int rcvlowat,
const struct bpf_prog_aux *aux)
{
u32 moff = aux->attach_st_ops_member_off;
bool wakeup = false;
if (moff == offsetof(struct bpf_tcp_ops, dequeue_rcvq))
wakeup = true;
if (rcvlowat < 0)
rcvlowat = INT_MAX;
return __tcp_set_rcvlowat(sk, rcvlowat, wakeup);
}
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(bpf_tcp_ops_set_flags_kfunc_set)
BTF_ID_FLAGS(func, bpf_tcp_ops_set_flags)
BTF_KFUNCS_END(bpf_tcp_ops_set_flags_kfunc_set)
BTF_KFUNCS_START(bpf_tcp_ops_set_rcvlowat_kfunc_set)
BTF_ID_FLAGS(func, bpf_tcp_ops_set_rcvlowat, KF_IMPLICIT_ARGS)
BTF_KFUNCS_END(bpf_tcp_ops_set_rcvlowat_kfunc_set)
static int bpf_tcp_ops_set_flags_kfunc_filter(const struct bpf_prog *prog,
u32 kfunc_id)
{
@ -390,6 +409,31 @@ static const struct btf_kfunc_id_set bpf_tcp_ops_set_flags_kfunc_id_set = {
.filter = bpf_tcp_ops_set_flags_kfunc_filter,
};
static int bpf_tcp_ops_set_rcvlowat_kfunc_filter(const struct bpf_prog *prog,
u32 kfunc_id)
{
u32 moff;
if (!btf_id_set8_contains(&bpf_tcp_ops_set_rcvlowat_kfunc_set, kfunc_id))
return 0;
if (prog->aux->st_ops != &bpf_tcp_ops)
return -EACCES;
moff = prog->aux->attach_st_ops_member_off;
if (moff != offsetof(struct bpf_tcp_ops, enqueue_rcvq) &&
moff != offsetof(struct bpf_tcp_ops, dequeue_rcvq))
return -EACCES;
return 0;
}
static const struct btf_kfunc_id_set bpf_tcp_ops_set_rcvlowat_kfunc_id_set = {
.owner = THIS_MODULE,
.set = &bpf_tcp_ops_set_rcvlowat_kfunc_set,
.filter = bpf_tcp_ops_set_rcvlowat_kfunc_filter,
};
static int __init __bpf_tcp_ops_init(void)
{
int ret;
@ -399,6 +443,8 @@ static int __init __bpf_tcp_ops_init(void)
/* BPF_PROG_TYPE_CGROUP_{SOCKOPT,SKB} share BTF_KFUNC_HOOK_CGROUP. */
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SOCKOPT,
&bpf_tcp_ops_set_flags_kfunc_id_set);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
&bpf_tcp_ops_set_rcvlowat_kfunc_id_set);
ret = ret ?: register_bpf_struct_ops(&bpf_tcp_ops, bpf_tcp_ops);
return ret;