netdev - Re: [PATCH net-next 2/3] bpf: add TCP_BPF_RTO_MAX for bpf

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Message-ID: <CAL+tcoATv6HX5G6wOrquGyyj8C7bFgRZNnWBwnPTKD1gb4ZD=g@mail.gmail.com>
Date: Fri, 14 Feb 2025 07:57:21 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org, 
	ncardwell@...gle.com, kuniyu@...zon.com, bpf@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] bpf: add TCP_BPF_RTO_MAX for bpf_setsockopt

On Fri, Feb 14, 2025 at 7:41 AM Stanislav Fomichev <stfomichev@...il.com> wrote:
>
> On 02/13, Jason Xing wrote:
> > Support bpf_setsockopt() to set the maximum value of RTO for
> > BPF program.
> >
> > Signed-off-by: Jason Xing <kerneljasonxing@...il.com>
> > ---
> >  Documentation/networking/ip-sysctl.rst | 3 ++-
> >  include/uapi/linux/bpf.h               | 2 ++
> >  net/core/filter.c                      | 6 ++++++
> >  tools/include/uapi/linux/bpf.h         | 2 ++
> >  4 files changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> > index 054561f8dcae..78eb0959438a 100644
> > --- a/Documentation/networking/ip-sysctl.rst
> > +++ b/Documentation/networking/ip-sysctl.rst
> > @@ -1241,7 +1241,8 @@ tcp_rto_min_us - INTEGER
> >
> >  tcp_rto_max_ms - INTEGER
> >       Maximal TCP retransmission timeout (in ms).
> > -     Note that TCP_RTO_MAX_MS socket option has higher precedence.
> > +     Note that TCP_BPF_RTO_MAX and TCP_RTO_MAX_MS socket option have the
> > +     higher precedence for configuring this setting.
>
> The cover letter needs more explanation about the motivation. And
> the precedence as well.

I am targeting the net-next tree because of recent changes[1] made by
Eric. It probably hasn't merged into the bpf-next tree.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=ae9b3c0e79bc

>
> WRT precedence, can you install setsockopt cgroup program and filter out
> calls to TCP_RTO_MAX_MS?

Yesterday, as suggested by Kuniyuki, I decided to re-use the same
logic of TCP_RTO_MAX_MS for bpf_setsockopt():
diff --git a/net/core/filter.c b/net/core/filter.c
index 2ec162dd83c4..ffec7b4357f9 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5382,6 +5382,7 @@ static int sol_tcp_sockopt(struct sock *sk, int optname,
        case TCP_USER_TIMEOUT:
        case TCP_NOTSENT_LOWAT:
        case TCP_SAVE_SYN:
+       case TCP_RTO_MAX_MS:
                if (*optlen != sizeof(int))
                        return -EINVAL;
                break;

Are you referring to using the previous way (by introducing a new flag
for BPF) because we need to know the explicit precedence between
setsockopt() and bpf_setsockopt() or other reasons? If so, I think
there are more places than setsockopt() to modify.

And, sorry that I don't follow what you meant by saying "install
setsockopt cgroup program" here. Please provide more hints.

Thanks for the review:)

Thanks,
Jason