Re: [PATCH v7 3/5] tcp: Resend SYN for inbound connections

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 7 Nov 2025 17:56:54 +0800
Yumei Huang <yuhuang@redhat.com> wrote:

> On Wed, Nov 5, 2025 at 3:01 PM Stefano Brivio <sbrivio@redhat.com> wrote:
> >
> > On Wed, 5 Nov 2025 15:24:44 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> >  
> > > On Tue, Nov 04, 2025 at 05:42:33AM +0100, Stefano Brivio wrote:  
> > > > On Fri, 31 Oct 2025 13:42:40 +0800
> > > > Yumei Huang <yuhuang@redhat.com> wrote:  
> > > [snip]  
> > > > > +/**
> > > > > + * tcp_get_rto_params() - Get host kernel RTO parameters
> > > > > + * @c:           Execution context
> > > > > +*/
> > > > > +void tcp_get_rto_params(struct ctx *c)
> > > > > +{
> > > > > + intmax_t tcp_syn_retries, syn_linear_timeouts;
> > > > > +
> > > > > + tcp_syn_retries = read_file_integer(
> > > > > +         TCP_SYN_RETRIES, TCP_SYN_RETRIES_DEFAULT);
> > > > > + syn_linear_timeouts = read_file_integer(
> > > > > +         TCP_SYN_LINEAR_TIMEOUTS, TCP_SYN_LINEAR_TIMEOUTS_DEFAULT);  
> > > >
> > > > I think this is a bit hard to read. Now:
> > > >
> > > >     tcp_syn_retries = read_file_integer(TCP_SYN_RETRIES,
> > > >                                         TCP_SYN_RETRIES_DEFAULT);
> > > >     syn_linear_timeouts = read_file_integer(TCP_SYN_LINEAR_TIMEOUTS,
> > > >                                             TCP_SYN_LINEAR_TIMEOUTS_DEFAULT);
> > > >
> > > > would be a bit closer to the coding style we're adopting, but I wonder:
> > > >
> > > > - does read_file_integer() really need to have "integer" in the name?  
> > >  
> > > >   In a language where integers are called 'int', perhaps
> > > >   read_file_int() is clear enough?  
> > >
> > > I think the idea is that read_file_integer() can be used for any
> > > (signed) integer type (with range checking performed after the call).
> > > read_file_int() might suggest it reads exactly an 'int', not anything
> > > bigger or smaller.  
> >
> > Oh, I see. It could be read_file_num() then, even if it's slightly less
> > accurate, or it can even remain read_file_integer(). If something like
> > this:
> >
> >         v = read_file_integer(SYN_RETRIES, SYN_RETRIES_DEFAULT);
> >         c->tcp.tcp_syn_retries = MIN(v, UINT8_MAX);
> >
> >         v = read_file_integer(SYN_LINEAR_TIMEOUTS, SYN_LINEAR_TIMEOUTS_DEFAULT);
> >         c->tcp.syn_linear_timeouts = MIN(v, UINT8_MAX);
> >
> > fits 80 columns, I'm taking it as a sign that the function name isn't
> > exceedingly long. No particular preference from me.  
> 
> The longest line just exceeds 80 columns.

No, why? It's 80 columns, look:

	v = read_file_integer(SYN_LINEAR_TIMEOUTS, SYN_LINEAR_TIMEOUTS_DEFAULT);
01234567890123456789012345678901234567890123456789012345678901234567890123456789

> I can rename the function to read_file_num() if there is no objection from David.

Sure, up to you and David.

> Another thing, while I was revising the patches, I noticed the
> parameter "const struct ctx *c" was removed from tcp_timer_ctl() by
> commit dd5302dd7bf51 ("tcp, flow: Replace per-connection in_epoll flag
> with an epollid in flow_common") from Laurent, but we need it to
> access c->tcp.syn_retries and c->tcp.syn_linear_timeouts. Should we
> add it back?

Yes, I don't see any other way around it, and I think I'll need it back
anyway for some fixes I'm working on.

It's one type of trivial conflict I would typically fix up on merge, by
the way, but given that you will send another version, you could/should
rebase on latest HEAD anyway.

> (Adding Laurent in the loop.)

-- 
Stefano