carp: allow commands to use interface name rather than index

[kp]

Summary

Get/set commands can now choose to provide the interface name rather
than the interface index. This allows userspace to avoid a call to
if_nametoindex().

Suggested by: melifaro
Sponsored by: Rubicon Communications, LLC ("Netgate")

[zlei]

sys/netinet/ip_carp.c

2354

Is it valid that both ifname and ifindex provided ?

And ifindex have default value 0, can not simply assert ifindex is provided.

[zlei]

sys/netinet/ip_carp.c

2354

And ifindex have default value 0, can not simply assert ifindex is provided.

Sorry that is not true.

if (ifindex == 0) {
		ifconfig_error(h, NETLINK, ENOENT);
		return (-1);
	}

[kp]

sys/netinet/ip_carp.c

2354

Userspace could provide both, but we're only going to use one of them. In this case, we'd use the name and ignore the index.

It wouldn't break anything, but it's obviously a silly thing for userspace to do.

[melifaro]

LGTM, thank you!

sys/netinet/ip_carp.c

2352

Nit; to mark the preference/intent, I’d check if the attribute is set