On Tue, May 05, 2026 at 11:08:27AM +0200, Laurent Vivier wrote:
> On 5/5/26 01:11, 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>
> > 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 f035fd3..75b8291 100644
> > --- a/conf.c
> > +++ b/conf.c
> > @@ -2159,15 +2159,14 @@ 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..35b9e2b 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;
> 
> Perhaps we can reset fwd->count and fwd->sock_count in fwd_listen_close() as
> after fwd_listen_close() these values are wrong?

No, they're not.  fwd_listen_close() closes the listening sockets, but
it doesn't remove the rules.  fwd->sock_count isn't the number of
*open* listening sockets, it's the maximum potential number of sockets
for all the rules.  Having some or all of the sockets close (-1 stored
in the array) is an allowed state.  It's rare for most rules, but
routine for SCAN ("auto") rules.

> > +	}
> > +
> > +	/* Swap active and pending tables */
> > +	static_assert(sizeof(tmp) == sizeof(c->fwd) &&
> > +		      sizeof(tmp) == sizeof(c->fwd_pending),
> > +		      "Temporary has wrong size");
> > +	memcpy(&tmp, (void *)c->fwd, sizeof(tmp));
> > +	memcpy((void *)c->fwd, (void *)c->fwd_pending, sizeof(tmp));
> > +	memcpy((void *)c->fwd_pending, &tmp, sizeof(tmp));
> 
> I know we have the static_assert(), but with memcpy() we usually use the
> sizeof() of the destination to avoid write overflow.
> 
> Why do we keep the old active table? Do we plan to have a "--restore" option?

Sort of.  There are two reasons we keep the table around.  One is
allow for at rollback if switching to the new one fails.  The other is
that we'll need it in order to allow for rule changes without
interrupting listening sockets.

> > +
> > +	/* Start listening on the new tables */
> > +	if (fwd_listen_init(c) < 0)
> > +		err("Error switching to new forwarding rules");
> > +}
> > +
> >   /* See enum in kernel's include/net/tcp_states.h */
> >   #define UDP_LISTEN	0x07
> >   #define TCP_LISTEN	0x0a
> > diff --git a/fwd.h b/fwd.h
> > index ac24782..b60697d 100644
> > --- a/fwd.h
> > +++ b/fwd.h
> > @@ -61,6 +61,7 @@ int fwd_listen_sync(const struct ctx *c, uint8_t pif,
> >   		    const struct fwd_scan *tcp, const struct fwd_scan *udp);
> >   void fwd_listen_close(const struct fwd_table *fwd);
> >   int fwd_listen_init(const struct ctx *c);
> > +void fwd_listen_switch(struct ctx *c);
> >   bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
> >   		 union inany_addr *translated);
> 

-- 
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