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

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Message-ID: <CAL+tcoCk_RTp6EBiRQ96nrdN7cuY1z+zxzxepyar4nXEJkAB9A@mail.gmail.com>
Date: Wed, 10 Apr 2024 20:54:51 +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

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);
>
> I get that 'int' is used instead of 'enum sk_rst_reason' to allow
> passing drop reasons too without casting, but that makes understanding

Yes!

> 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.

>
> 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

It, indeed, looks better (clean and clear) :)

So I also ought to adjust the trace_tcp_send_reset part...

Thanks,
Jason