Re: [PATCH v2 6/9] conf: Allow multiple -a/--address options per address family

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

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On Sun, Jan 18, 2026 at 05:16:09PM -0500, Jon Maloy wrote:
> We enable configuration of multiple IPv4 and IPv6 addresses by allowing
> repeated use of the -a/--address option.
> 
> - We update option parsing to append addresses to the addrs[] array.
> - Each address specified via -a does initially get a class-based default
>   prefix.
> - If no -a option is given, address and prefix are inherited from
>   the template interface.
> - If a prefix length is to be added, it has to be done in CIDR format,
>   except for the very first address.
> - We configure all indicated addresses in the namespace interface.
> 
> Signed-off-by: Jon Maloy <jmaloy@redhat.com>
> 
> ---
> v2: Adapted to previous code changes
> ---
>  conf.c  | 42 +++++++++++++++++++++++++++++-------------
>  pasta.c | 24 ++++++++++++++++++------
>  2 files changed, 47 insertions(+), 19 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 3ecd1a0..32a754d 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -789,7 +789,7 @@ static unsigned int conf_ip4(unsigned int ifi, struct ip4_ctx *ip4)
>  
>  	ip4->our_tap_addr = ip4->guest_gw;
>  
> -	if (inany_is_unspecified(&ip4->addrs[0].addr))
> +	if (!ip4->addr_count)
>  		return 0;
>  
>  	return ifi;
> @@ -858,8 +858,7 @@ static unsigned int conf_ip6(unsigned int ifi, struct ip6_ctx *ip6)
>  	if (IN6_IS_ADDR_LINKLOCAL(&ip6->guest_gw))
>  		ip6->our_tap_ll = ip6->guest_gw;
>  
> -	if (IN6_IS_ADDR_UNSPECIFIED(&ip6->addrs[0].addr.a6) ||
> -	    IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
> +	if (!ip6->addr_count || IN6_IS_ADDR_UNSPECIFIED(&ip6->our_tap_ll))
>  		return 0;
>  
>  	return ifi;
> @@ -951,9 +950,11 @@ static void usage(const char *name, FILE *f, int status)
>  		"    default: 65520: maximum 802.3 MTU minus 802.3 header\n"
>  		"                    length, rounded to 32 bits (IPv4 words)\n"
>  		"  -a, --address ADDR	Assign IPv4 or IPv6 address ADDR[/PREFIXLEN]\n"
> -		"    can be specified zero to two times (for IPv4 and IPv6)\n"
> +		"    can be specified multiple times (limit: %d IPv4, %d IPv6)\n"
>  		"    default: use addresses from interface with default route\n"
> -		"  -n, --netmask MASK	Assign IPv4 MASK, dot-decimal or bits\n"
> +		"  -n, --netmask MASK	Assign IPv4 MASK, dot-decimal or bits\n",
> +		IP4_MAX_ADDRS, IP6_MAX_ADDRS);
> +	FPRINTF(f,
>  		"    default: netmask from matching address on the host\n"
>  		"  -M, --mac-addr ADDR	Use source MAC address ADDR\n"
>  		"    default: 9a:55:9a:55:9a:55 (locally administered)\n"
> @@ -1882,6 +1883,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  			union inany_addr addr;
>  			const struct in_addr *a4;
>  			int prefix_len = 0;
> +			unsigned int i;
>  			int af;
>  
>  			af = conf_addr_prefix_len(optarg, &addr, &prefix_len);
> @@ -1893,9 +1895,15 @@ void conf(struct ctx *c, int argc, char **argv)
>  				die("Invalid address: %s", optarg);
>  
>  			if (af == AF_INET6) {
> -				c->ip6.addrs[0].addr.a6 = addr.a6;
> -				c->ip6.addrs[0].flags |= INANY_ADDR_CONFIGURED;
> -				c->ip6.addr_count = 1;
> +				i = c->ip6.addr_count;
> +
> +				if (i >= IP6_MAX_ADDRS)
> +					die("Too many IPv6 addresses");
> +
> +				c->ip6.addrs[i].addr.a6 = addr.a6;
> +				c->ip6.addrs[i].prefix_len = prefix_len;
> +				c->ip6.addrs[i].flags = INANY_ADDR_CONFIGURED;
> +				c->ip6.addr_count++;

This is getting moderately deeply nested.  Maybe worth creating an
"add_address" helper?  That could also be helpful if we later
integrate the addr_seen stuff into the same table.

>  				if (c->mode == MODE_PASTA)
>  					c->ip6.no_copy_addrs = true;
>  				break;
> @@ -1904,10 +1912,15 @@ void conf(struct ctx *c, int argc, char **argv)
>  			a4 = inany_v4(&addr);
>  
>  			if (af == AF_INET && a4) {
> -				c->ip4.addrs[0].addr = inany_from_v4(*a4);
> -				c->ip4.addrs[0].flags |= INANY_ADDR_CONFIGURED;
> -				c->ip4.addr_count = 1;
> -				if (prefix_len) {
> +				i = c->ip4.addr_count;
> +
> +				if (i >= IP4_MAX_ADDRS)
> +					die("Too many IPv4 addresses");
> +
> +				c->ip4.addrs[i].addr = inany_from_v4(*a4);
> +				c->ip4.addrs[i].prefix_len = prefix_len;
> +				c->ip4.addrs[i].flags = INANY_ADDR_CONFIGURED;
> +				if (i == 0 && prefix_len) {
>  					if (prefix_from_opt)
>  						die("Can't mix CIDR with -n");
>  					prefix_from_cidr = true;
> @@ -1915,6 +1928,9 @@ void conf(struct ctx *c, int argc, char **argv)
>  					prefix_len = ip4_default_prefix_len(a4);
>  				}
>  				c->ip4.addrs[0].prefix_len = prefix_len;
> +				c->ip4.addr_count++;
> +				if (c->mode == MODE_PASTA)
> +					c->ip4.no_copy_addrs = true;
>  				break;
>  			}
>  
> @@ -2217,7 +2233,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  	if (!c->ifi6) {
>  		c->no_ndp = 1;
>  		c->no_dhcpv6 = 1;
> -	} else if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addrs[0].addr.a6)) {
> +	} else if (!c->ip6.addr_count) {
>  		c->no_dhcpv6 = 1;

Kind of pre-existing, but AFAICT we entirely disable IPv6 (ifi6 == 0)
if we have no addresses - that would seem to superseded disabling just
DHCPv6.

>  	}
>  
> diff --git a/pasta.c b/pasta.c
> index 1bb3dd0..27ce6a7 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -338,10 +338,16 @@ void pasta_ns_conf(struct ctx *c)
>  
>  		if (c->ifi4) {
>  			if (c->ip4.no_copy_addrs) {
> -				rc = nl_addr_set(nl_sock_ns, c->pasta_ifi,
> -						 AF_INET,
> -						 inany_v4(&c->ip4.addrs[0].addr),
> -						 c->ip4.addrs[0].prefix_len);
> +				int i;
> +
> +				for (i = 0; i < c->ip4.addr_count; i++) {
> +					rc = nl_addr_set(nl_sock_ns,
> +							 c->pasta_ifi, AF_INET,
> +							 inany_v4(&c->ip4.addrs[i].addr),
> +							 c->ip4.addrs[i].prefix_len);
> +					if (rc < 0)
> +						break;
> +				}
>  			} else {
>  				rc = nl_addr_dup(nl_sock, c->ifi4,
>  						 nl_sock_ns, c->pasta_ifi,
> @@ -387,12 +393,18 @@ void pasta_ns_conf(struct ctx *c)
>  					  0, IFF_NOARP);
>  
>  			if (c->ip6.no_copy_addrs) {
> -				struct in6_addr *a = &c->ip6.addrs[0].addr.a6;
> +				struct in6_addr *a;
> +				int i;
>  
> -				if (!IN6_IS_ADDR_UNSPECIFIED(a)) {
> +				for (i = 0; i < c->ip6.addr_count; i++) {
> +					a = &c->ip6.addrs[i].addr.a6;
> +					if (IN6_IS_ADDR_UNSPECIFIED(a))
> +						continue;
>  					rc = nl_addr_set(nl_sock_ns,
>  							 c->pasta_ifi,
>  							 AF_INET6, a, 64);
> +					if (rc < 0)
> +						break;
>  				}
>  			} else {
>  				rc = nl_addr_dup(nl_sock, c->ifi6,
> -- 
> 2.52.0
> 

-- 
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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