Re: [PATCH iproute2-next] ipaddress: add support for showing IPv4 devconf attributes

[Fernando Fernandez Mancera <fmancera@suse.de>]

On 6/13/26 4:29 AM, Stephen Hemminger wrote:
> On Sat, 13 Jun 2026 01:17:22 +0200
> Fernando Fernandez Mancera <fmancera@suse.de> wrote:
> 
>> tatic void print_inet(FILE *fp, struct rtattr *inet_attr)
>> +{
>> +	struct rtattr *tb[IFLA_INET_MAX + 1];
>> +
>> +	parse_rtattr_nested(tb, IFLA_INET_MAX, inet_attr);
>> +
>> +	if (tb[IFLA_INET_CONF] && show_details) {
>> +		int *conf = RTA_DATA(tb[IFLA_INET_CONF]);
>> +		int max_elements = RTA_PAYLOAD(tb[IFLA_INET_CONF]) / sizeof(int);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_FORWARDING)
>> +			print_string(PRINT_ANY, "forwarding", "forwarding %s ",
>> +				     conf[IPV4_DEVCONF_FORWARDING - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_MC_FORWARDING)
>> +			print_string(PRINT_ANY, "mc_forwarding", "mc_forwarding %s ",
>> +				     conf[IPV4_DEVCONF_MC_FORWARDING - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_PROXY_ARP)
>> +			print_string(PRINT_ANY, "proxy_arp", "proxy_arp %s ",
>> +				     conf[IPV4_DEVCONF_PROXY_ARP - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ACCEPT_REDIRECTS)
>> +			print_string(PRINT_ANY, "accept_redirects",
>> +				     "accept_redirects %s ",
>> +				     conf[IPV4_DEVCONF_ACCEPT_REDIRECTS - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_SECURE_REDIRECTS)
>> +			print_string(PRINT_ANY, "secure_redirects",
>> +				     "secure_redirects %s ",
>> +				     conf[IPV4_DEVCONF_SECURE_REDIRECTS - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_SEND_REDIRECTS)
>> +			print_string(PRINT_ANY, "send_redirects", "send_redirects %s ",
>> +				     conf[IPV4_DEVCONF_SEND_REDIRECTS - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_SHARED_MEDIA)
>> +			print_string(PRINT_ANY, "shared_media", "shared_media %s ",
>> +				     conf[IPV4_DEVCONF_SHARED_MEDIA - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_RP_FILTER)
>> +			print_int(PRINT_ANY, "rp_filter", "rp_filter %d ",
>> +				  conf[IPV4_DEVCONF_RP_FILTER - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ACCEPT_SOURCE_ROUTE)
>> +			print_string(PRINT_ANY, "accept_source_route",
>> +				     "accept_source_route %s ",
>> +				     conf[IPV4_DEVCONF_ACCEPT_SOURCE_ROUTE - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_BOOTP_RELAY)
>> +			print_string(PRINT_ANY, "bootp_relay", "bootp_relay %s ",
>> +				     conf[IPV4_DEVCONF_BOOTP_RELAY - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_LOG_MARTIANS)
>> +			print_string(PRINT_ANY, "log_martians", "log_martians %s ",
>> +				     conf[IPV4_DEVCONF_LOG_MARTIANS - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_TAG)
>> +			print_int(PRINT_ANY, "tag", "tag %d ",
>> +				  conf[IPV4_DEVCONF_TAG - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARPFILTER)
>> +			print_string(PRINT_ANY, "arpfilter", "arpfilter %s ",
>> +				     conf[IPV4_DEVCONF_ARPFILTER - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_MEDIUM_ID)
>> +			print_int(PRINT_ANY, "medium_id", "medium_id %d ",
>> +				  conf[IPV4_DEVCONF_MEDIUM_ID - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_NOXFRM)
>> +			print_string(PRINT_ANY, "noxfrm", "noxfrm %s ",
>> +				     conf[IPV4_DEVCONF_NOXFRM - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_NOPOLICY)
>> +			print_string(PRINT_ANY, "nopolicy", "nopolicy %s ",
>> +				     conf[IPV4_DEVCONF_NOPOLICY - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_FORCE_IGMP_VERSION)
>> +			print_int(PRINT_ANY, "force_igmp_version", "force_igmp_version %d ",
>> +				  conf[IPV4_DEVCONF_FORCE_IGMP_VERSION - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARP_ANNOUNCE)
>> +			print_int(PRINT_ANY, "arp_announce", "arp_announce %d ",
>> +				  conf[IPV4_DEVCONF_ARP_ANNOUNCE - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARP_IGNORE)
>> +			print_int(PRINT_ANY, "arp_ignore", "arp_ignore %d ",
>> +				  conf[IPV4_DEVCONF_ARP_IGNORE - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_PROMOTE_SECONDARIES)
>> +			print_string(PRINT_ANY, "promote_secondaries",
>> +				     "promote_secondaries %s ",
>> +				     conf[IPV4_DEVCONF_PROMOTE_SECONDARIES - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARP_ACCEPT)
>> +			print_int(PRINT_ANY, "arp_accept", "arp_accept %d ",
>> +				  conf[IPV4_DEVCONF_ARP_ACCEPT - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARP_NOTIFY)
>> +			print_string(PRINT_ANY, "arp_notify", "arp_notify %s ",
>> +				     conf[IPV4_DEVCONF_ARP_NOTIFY - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ACCEPT_LOCAL)
>> +			print_string(PRINT_ANY, "accept_local", "accept_local %s ",
>> +				     conf[IPV4_DEVCONF_ACCEPT_LOCAL - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_SRC_VMARK)
>> +			print_string(PRINT_ANY, "src_vmark", " src_vmark %s",
>> +				     conf[IPV4_DEVCONF_SRC_VMARK - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_PROXY_ARP_PVLAN)
>> +			print_string(PRINT_ANY, "proxy_arp_pvlan", "proxy_arp_pvlan %s ",
>> +				     conf[IPV4_DEVCONF_PROXY_ARP_PVLAN - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ROUTE_LOCALNET)
>> +			print_string(PRINT_ANY, "route_localnet", "route_localnet %s ",
>> +				     conf[IPV4_DEVCONF_ROUTE_LOCALNET - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_BC_FORWARDING)
>> +			print_string(PRINT_ANY, "bc_forwarding", "bc_forwarding %s ",
>> +				     conf[IPV4_DEVCONF_BC_FORWARDING - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL)
>> +			print_int(PRINT_ANY, "igmpv2_unsolicited_report_interval",
>> +				  "igmpv2_unsolicited_report_interval %d ",
>> +				  conf[IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL)
>> +			print_int(PRINT_ANY, "igmpv3_unsolicited_report_interval",
>> +				  "igmpv3_unsolicited_report_interval %d ",
>> +				  conf[IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL - 1]);
>> +
>> +		if (max_elements >= IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN)
>> +			print_string(PRINT_ANY, "ignore_routes_with_linkdown",
>> +				     "ignore_routes_with_linkdown %s ",
>> +				     conf[IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN - 1] ?
>> +				     "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST)
>> +			print_string(PRINT_ANY, "drop_unicast_in_l2_multicast",
>> +				     "drop_unicast_in_l2_multicast %s ",
>> +				     conf[IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST - 1] ?
>> +				     "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_DROP_GRATUITOUS_ARP)
>> +			print_string(PRINT_ANY, "drop_gratuitous_arp",
>> +				     "drop_gratuitous_arp %s ",
>> +				     conf[IPV4_DEVCONF_DROP_GRATUITOUS_ARP - 1] ? "on" : "off");
>> +
>> +		if (max_elements >= IPV4_DEVCONF_ARP_EVICT_NOCARRIER)
>> +			print_string(PRINT_ANY, "arp_evict_nocarrier",
>> +				     "arp_evict_nocarrier %s ",
>> +				     conf[IPV4_DEVCONF_ARP_EVICT_NOCARRIER - 1] ? "on" : "off");
>> +	}
>> +}
>> +
> There are three different ways to display a flag value in JSON used in iproute2.
> This one is my least favorite.
> 
> The three ways are:
>     - print_bool
>     - print_null (only if on)
>     - print_string
> 
> I would use the print_null pattern but print_bool would also be ok.
> 

Thanks for the suggestion Stephen, I would pick print_bool in this case.

If one of the options evolves to supporting something else we could 
easily adapt it without breaking compatibility if we use print_bool. If 
we use print_null I don't think we could do that.

Thanks,
Fernando.