Re: [PATCH v8 17/19] conf, fwd: Allow switching to new rules received from pesto

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 06, 2026 at 10:49:55AM +0200, Stefano Brivio wrote:
> On Wed, 6 May 2026 10:39:30 +0200
> Stefano Brivio <sbrivio@redhat.com> wrote:
> 
> > On Wed, 6 May 2026 10:12:21 +0200
> > Laurent Vivier <lvivier@redhat.com> wrote:
> > 
> > > On 5/6/26 01:47, Stefano Brivio wrote:  
> > > > From: David Gibson <david@gibson.dropbear.id.au>
> > > > 
> > > > We can now receive updates to the forwarding rules from the pesto client
> > > > and store them in a "pending" copy of the forwarding tables.  Implement
> > > > switching to using the new rules.
> > > > 
> > > > The logic is in a new fwd_listen_switch().  For now this closes all
> > > > listening sockets related to the old tables, swaps the active and pending
> > > > tables, then listens based on the new tables.  In future we look to improve
> > > > this so that we don't temporarily stop listening on ports that both the
> > > > old and new tables specify.
> > > > 
> > > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > > > [sbrivio: In fwd_listen_switch(), use the destination size as argument
> > > >   to memcpy(), instead of sizeof(tmp), as suggested by Laurent]
> > > > Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> > > > ---
> > > >   conf.c |  5 ++---
> > > >   fwd.c  | 34 ++++++++++++++++++++++++++++++++++
> > > >   fwd.h  |  1 +
> > > >   3 files changed, 37 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/conf.c b/conf.c
> > > > index 76344da..3f48793 100644
> > > > --- a/conf.c
> > > > +++ b/conf.c
> > > > @@ -2160,15 +2160,14 @@ void conf_handler(struct ctx *c, uint32_t events)
> > > >   			fwd_rules_dump(info, fwd->rules, fwd->count,
> > > >   				       "    ", "");
> > > >   		}
> > > > +
> > > > +		fwd_listen_switch(c);
> > > >   	}
> > > >   
> > > >   	if (events & EPOLLHUP) {
> > > >   		debug("Configuration client hangup");
> > > > -		goto close;
> > > >   	}
> > > >   
> > > > -	return;
> > > > -
> > > >   close:
> > > >   	conf_close(c);
> > > >   
> > > > diff --git a/fwd.c b/fwd.c
> > > > index d93d2e5..0697435 100644
> > > > --- a/fwd.c
> > > > +++ b/fwd.c
> > > > @@ -534,6 +534,40 @@ int fwd_listen_init(const struct ctx *c)
> > > >   	return 0;
> > > >   }
> > > >   
> > > > +/**
> > > > + * fwd_listen_switch() - Switch from current to pending rules table
> > > > + * @c:		Execution context
> > > > + */
> > > > +void fwd_listen_switch(struct ctx *c)
> > > > +{
> > > > +	struct fwd_table *tmp[PIF_NUM_TYPES];
> > > > +	unsigned i;
> > > > +
> > > > +	/* Stop listening on the old tables */
> > > > +	for (i = 0; i < PIF_NUM_TYPES; i++) {
> > > > +		struct fwd_table *fwd = c->fwd[i];
> > > > +
> > > > +		if (!fwd)
> > > > +			continue;
> > > > +
> > > > +		debug("Flushing %u old %s rules", fwd->count, pif_name(i));
> > > > +		fwd_listen_close(fwd);
> > > > +		fwd->count = fwd->sock_count = 0;
> > > > +	}
> > > > +
> > > > +	/* Swap active and pending tables */
> > > > +	static_assert(sizeof(tmp) == sizeof(c->fwd) &&
> > > > +		      sizeof(tmp) == sizeof(c->fwd_pending),
> > > > +		      "Temporary has wrong size");    
> > > 
> > > At this point:
> > > 
> > > c->fwd[PIF_HOST] = &fwd_in;
> > > c->fwd[PIF_SPLICE] = &fwd_out;
> > > 
> > > c->fwd_pending[PIF_HOST] = &fwd_in_pending;
> > > c->fwd_pending[PIF_SPLICE] = &fwd_out_pending;
> > >   
> > > > +	memcpy(&tmp, (void *)c->fwd, sizeof(tmp));
> > > > +	memcpy((void *)c->fwd, (void *)c->fwd_pending, sizeof(c->fwd));
> > > > +	memcpy((void *)c->fwd_pending, &tmp, sizeof(c->fwd_pending));    
> > > 
> > > At this point:
> > > 
> > > c->fwd[PIF_HOST] = &fwd_in_pending;
> > > c->fwd[PIF_SPLICE] = &fwd_out_pending;
> > > 
> > > c->fwd_pending[PIF_HOST] = &fwd_in;
> > > c->fwd_pending[PIF_SPLICE] = &fwd_out;  
> > 
> > Yeah, makes sense, I can change that in v9.
> > 
> > > Perhaps it should be noted somewhere to avoid confusion in the future?  
> > 
> > What do you think should be noted exactly, and where? Can you show a
> > practical example of the change you're proposing?
> 
> ...I'm leaving like it is in v9 to make sure I'm not misinterpreting
> you, and also because the current (v8) version is obviously correct and
> I also tested it fairly heavily by now.
> 
> I'd suggest optimising this (and commenting as needed) in a separate
> patch later.

As noted in another branch of this thread, I think all it really needs
is renaming the globals that c->fwd and c->fwd_pending point to.  They
should just be fwd_in_[12] (or an array of 2 tables), instead of
implying a semantic difference between the plain and "pending" copies.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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