netdev - Re: [PATCH net-next v3 2/6] rstreason: prepare for passive reset

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Message-ID: <CAL+tcoBpAOhbLC5TqwMBG6Q3hgiJYSV+ZAkZfLPNmG_OK22r1A@mail.gmail.com>
Date: Wed, 10 Apr 2024 21:55:21 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Antoine Tenart <atenart@...nel.org>
Cc: davem@...emloft.net, dsahern@...nel.org, edumazet@...gle.com, 
	geliang@...nel.org, kuba@...nel.org, martineau@...nel.org, 
	mathieu.desnoyers@...icios.com, matttbe@...nel.org, mhiramat@...nel.org, 
	pabeni@...hat.com, rostedt@...dmis.org, mptcp@...ts.linux.dev, 
	linux-trace-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 2/6] rstreason: prepare for passive reset

On Wed, Apr 10, 2024 at 9:21 PM Antoine Tenart <atenart@...nel.org> wrote:
>
> Quoting Jason Xing (2024-04-10 14:54:51)
> > Hi Antoine,
> >
> > On Wed, Apr 10, 2024 at 8:14 PM Antoine Tenart <atenart@...nel.org> wrote:
> > >
> > > Quoting Jason Xing (2024-04-09 12:09:30)
> > > >         void            (*send_reset)(const struct sock *sk,
> > > > -                                     struct sk_buff *skb);
> > > > +                                     struct sk_buff *skb,
> > > > +                                     int reason);
> >
> > > what should be 'reason' harder. Eg. when looking at the code or when
> > > using BTF (to then install debugging probes with BPF) this is not
> > > obvious.
> >
> > Only one number if we want to extract the reason with BPF, right? I
> > haven't tried it.
>
> Yes, we can get 'reason'. Knowing the type helps.
>
> > > A similar approach could be done as the one used for drop reasons: enum
> > > skb_drop_reason is used for parameters (eg. kfree_skb_reason) but other
> > > valid values (subsystem drop reasons) can be used too if casted (to
> > > u32). We could use 'enum sk_rst_reason' and cast the other values. WDYT?
> >
> > I have been haunted by this 'issue' for a long time...
> >
> > Are you suggesting doing so as below for readability:
> > 1) replace the reason parameter in all the related functions (like
> > .send_reset(), tcp_v4_send_reset(), etc) by using 'enum sk_rst_reason'
> > type?
> > 2) in patch [4/6], when it needs to pass the specific reason in those
> > functions, we can cast it to 'enum sk_rst_reason'?
> >
> > One modification I just made based on this patchset if I understand correctly:
> > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> > index 4889fccbf754..e0419b8496b5 100644
> > --- a/net/ipv4/tcp_ipv4.c
> > +++ b/net/ipv4/tcp_ipv4.c
> > @@ -725,7 +725,7 @@ static bool tcp_v4_ao_sign_reset(const struct sock
> > *sk, struct sk_buff *skb,
> >   */
> >
> >  static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb,
> > -                             int reason)
> > +                             enum sk_rst_reason reason)
> >  {
> >         const struct tcphdr *th = tcp_hdr(skb);
> >         struct {
> > @@ -1935,7 +1935,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
> >         return 0;
> >
> >  reset:
> > -       tcp_v4_send_reset(rsk, skb, reason);
> > +       tcp_v4_send_reset(rsk, skb, (enum sk_rst_reason)reason);
> >  discard:
> >         kfree_skb_reason(skb, reason);
> >         /* Be careful here. If this function gets more complicated and
> >
>
> That's right. I think (u32) can also be used for the cast to make the
> compiler happy in 2), but the above makes sense.

Got it :) Will update soon.

Thanks,
Jason