Re: [PATCH 1/3] fwd_rule: Parse target adddresses for forwarding rules

[Stefano Brivio <sbrivio@redhat.com>]

Nit, in the title: addresses.

On Wed,  1 Jul 2026 17:08:09 +1000
David Gibson <david@gibson.dropbear.id.au> wrote:

> Extend the parsing of forwarding rules (-[tu]) to allow the destination
> address on the target side to be specified.  For now just parse them, and
> give an error if we try to create rules with a specified target address.
> We'll implement the actual forwarding logic in another patch.
> 
> Format (for either command line or pesto):
>       -t 2222:192.0.2.1/2222
> 
> This should work along with all the other bits, that is, say:
>       -t 192.0.2.1%eth0/2222-2225:192.0.2.2/22-25
> 
> FIXME: Ban for -[TU] for now
> FIXME: Check interaction with splice handling
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> [dwg: Syntax from Stefano's earlier draft, largely rewritten on top of new
>  parsing helpers]
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  fwd_rule.c | 38 +++++++++++++++++++++++++++++++-------
>  1 file changed, 31 insertions(+), 7 deletions(-)
> 
> diff --git a/fwd_rule.c b/fwd_rule.c
> index ca409eaf..e8abc884 100644
> --- a/fwd_rule.c
> +++ b/fwd_rule.c
> @@ -378,14 +378,17 @@ int fwd_rule_add(struct fwd_table *fwd, const struct fwd_rule *new)
>   * @first:	First port to forward
>   * @last:	Last port to forward
>   * @exclude:	Bitmap of ports to exclude (may be NULL)
> - * @to:		Port to translate @first to when forwarding
> + * @tgt_addr:	Destination address on the target side
> + * @tgt_first:	Destination port to use for @first on the traget side

Nit: target.

>   * @flags:	Flags for forwarding entries
>   */
>  static void fwd_rule_range_except(struct fwd_table *fwd, bool del,
>  				  uint8_t proto, const union inany_addr *addr,
>  				  const char *ifname,
>  				  uint16_t first, uint16_t last,
> -				  const uint8_t *exclude, uint16_t to,
> +				  const uint8_t *exclude,
> +				  const union inany_addr *tgt_addr,
> +				  uint16_t tgt_first,
>  				  uint8_t flags)
>  {
>  	struct fwd_rule rule = {
> @@ -395,9 +398,17 @@ static void fwd_rule_range_except(struct fwd_table *fwd, bool del,
>  		.flags = flags,
>  	};
>  	char rulestr[FWD_RULE_STRLEN];
> -	unsigned delta = to - first;
> +	unsigned delta = tgt_first - first;

Nit: should be moved above now.

>  	unsigned base, i;
>  
> +	if (tgt_addr && !inany_is_unspecified(tgt_addr)) {
> +		char astr[INANY_ADDRSTRLEN];
> +
> +		info("Target address: %s",
> +		     inany_ntop(tgt_addr, astr, sizeof(astr)));
> +		die("Target address remapping not yet implemented");
> +	}
> +
>  	if (!addr)
>  		rule.flags |= FWD_DUAL_STACK_ANY;
>  	if (ifname) {
> @@ -458,14 +469,17 @@ enum fwd_port_chunk_kind {
>   * @cursor:	Parsing point (see parse.c)
>   * @kindp:	Updated with kind of chunk we parsed
>   * @lrange:	Updated with listening port range (for INCLUDE & EXCLUDE)
> + * @taddr:	Updated with target address (for INCLUDE)
>   * @trange:	Updated with target port range (for INCLUDE)
>   */
>  static bool parse_port_chunk(const char **cursor,
>  			     enum fwd_port_chunk_kind *kindp,
>  			     struct port_range *lrange,
> +			     union inany_addr *taddr,
>  			     struct port_range *trange)
>  {
>  	struct port_range lr = { 0 }, tr = { 0 };
> +	union inany_addr taddr_tmp = inany_any6;
>  	enum fwd_port_chunk_kind kind;
>  	const char *p = *cursor;
>  
> @@ -481,6 +495,12 @@ static bool parse_port_chunk(const char **cursor,
>  		kind = CHUNK_INCLUDE;
>  
>  		if (parse_literal(&p, ":")) {
> +			const char *tgtspec = p;
> +
> +			if (!parse_inany(&p, &taddr_tmp)	||
> +			    !parse_literal(&p, "/"))

This is to support ":/PORT" together with ":ADDR/PORT", right? I think
it's nice to have for users, but it looks inconsistent here, so maybe
you could add a comment before that, say:

			/* Accept :/PORT as well as :ADDR/PORT */

> +				p = tgtspec; /* No target address, backtrack */
> +
>  			if (!parse_port_range(&p, &tr))
>  				return false;
>  		} else {
> @@ -492,6 +512,8 @@ static bool parse_port_chunk(const char **cursor,
>  
>  	*kindp = kind;
>  	*lrange = lr;
> +	if (taddr)
> +		*taddr = taddr_tmp;
>  	if (trange)
>  		*trange = tr;
>  	*cursor = p;
> @@ -561,7 +583,7 @@ static void fwd_rule_parse_ports(struct fwd_table *fwd, bool del, uint8_t proto,
>  	/* Consider excluded ranges and "auto" in the first pass */
>  	p = spec;
>  	do {
> -		if (!parse_port_chunk(&p, &kind, &lrange, NULL))
> +		if (!parse_port_chunk(&p, &kind, &lrange, NULL, NULL))
>  			goto bad;
>  
>  		switch (kind) {
> @@ -586,8 +608,9 @@ static void fwd_rule_parse_ports(struct fwd_table *fwd, bool del, uint8_t proto,
>  	p = spec;
>  	do {
>  		struct port_range trange;
> +		union inany_addr taddr;
>  
> -		if (!parse_port_chunk(&p, &kind, &lrange, &trange))
> +		if (!parse_port_chunk(&p, &kind, &lrange, &taddr, &trange))
>  			goto bad;
>  
>  		switch (kind) {
> @@ -604,7 +627,8 @@ static void fwd_rule_parse_ports(struct fwd_table *fwd, bool del, uint8_t proto,
>  
>  			fwd_rule_range_except(fwd, del, proto, addr, ifname,
>  					      lrange.first, lrange.last,
> -					      exclude, trange.first, flags);
> +					      exclude, &taddr, trange.first,
> +					      flags);
>  			break;
>  		default:
>  			goto bad;
> @@ -620,7 +644,7 @@ static void fwd_rule_parse_ports(struct fwd_table *fwd, bool del, uint8_t proto,
>  
>  		fwd_rule_range_except(fwd, del, proto, addr, ifname,
>  				      1, NUM_PORTS - 1, exclude,
> -				      1, flags | FWD_WEAK);
> +				      NULL, 1, flags | FWD_WEAK);
>  	}
>  	return;
>  bad:

The rest of the series looks good to me, but I didn't test things at
all. By the way, man page and usage changes for 3/3 are missing.

I haven't seen anything preventing mapping between IPv4 and IPv6, but I
guess I missed something. I actually think it would be a nice feature
but I guess it needs some more effort to properly support it.

-- 
Stefano