arp: remove gethostby*() calls

[yanhaowang]

Summary

1. Use getaddrinfo to replace gethostbyname.
2. Use getnameinfo with NI_NAMEREQD flag to replace gethostbyaddr.

Test Plan

print_entry function in "arp.c" will be call when WITHOUT_NETLINK is define and print_entry function in "arp_netlink.c" will be call in opsite. I run arp -a in both case on revise and not revised code. it output same like below.

// Original
$ arp -a  // WITHOUT_NETLINK is defined
? (192.168.42.2) at 00:50:56:ef:d2:41 on le0 expires in 1020 seconds [ethernet]
? (192.168.42.128) at 00:0c:29:02:ba:a1 on le0 permanent [ethernet]

$ arp -a // WITHOUT_NETLINK is not defined
? (192.168.42.2) at 00:50:56:ef:d2:41 on le0 expires in 961 seconds [ethernet]
? (192.168.42.128) at 00:0c:29:02:ba:a1 on le0 permanent [ethernet]

// Revised
$ arp -a // WITHOUT_NETLINK is defined
? (192.168.42.2) at 00:50:56:ef:d2:41 on le0 expires in 1093 seconds [ethernet]
? (192.168.42.128) at 00:0c:29:02:ba:a1 on le0 permanent [ethernet]

$ arp -a // WITHOUT_NETLINK is not defined
? (192.168.42.2) at 00:50:56:ef:d2:41 on le0 expires in 1175 seconds [ethernet]
? (192.168.42.128) at 00:0c:29:02:ba:a1 on le0 permanent [ethernet]

As for the getaddr function I use sudo arp -d kola (kola is a hostname of my private IP, for testing the getaddrinfo function work) and sudo arp -d -a to test and it work fine (successfully delete the entry).

[yanhaowang]

Fix file permission.

[yanhaowang]

usr.sbin/arp/arp.c

262–267

Should I use memset to replace the bzero function?

[yanhaowang]

This comment was removed by yanhaowang.

[yanhaowang]

Revise error code

We should use EAI_AGAIN instead of TRY_AGAIN error code while using getnameinfo.

[yanhaowang]

• Remove for loop

[hrs]

The change basically looks good to me, but I added some comments.

usr.sbin/arp/arp.c

265

hints = (struct addrinfo){
    .ai_family = AF_INET
};

is enough for memset() + assignments.

613

sizeof() should be replaced with addr->sin_len.

I would recommend to change the type of addr to struct sockaddr, and define struct sockaddr_in *sin = (struct sockaddr_in *)addr at the top of this function to use it as sockaddr_in. This requires additional changes in search() and action_fn, though.

usr.sbin/arp/arp_netlink.c

188

The same as arp.c

[yanhaowang]

Revise according Hiroki advise

1. Use sin_len member.
2. Change function prototype from sockaddr_in to sockaddr. In this case we change action_fn, print_entry and nuke_entry function.
3. Use struct initializer to replace memset and assignments.

[hrs]

usr.sbin/arp/arp.c

267–272

Removing "hints" and use of compound literals will give a more compact idiom like this:

error = getaddrinfo(host, NULL, &(struct addrinfo){
    .ai_family = AF_INET
}, &res);

I would recommend to use "error" instead of "status" as the variable name because the conditional can be written like the following. I believe it is more intuitive:

if (error) {
 ...
}

268

Check whether the return value is EAI_SYSTEM or not. If it is EAI_SYSTEM, the error code must be extracted from errno, not the return value.

if (status != 0) {
    xo_warnx("%s: %s", host, (status == EAI_SYSTEM)
        ? strerror(errno)  : gai_strerror(status));
    return (NULL);
}

614

Use sizeof(hostbuf) instead of NI_MAXHOST.

usr.sbin/arp/arp_netlink.c

189

Same as L.613 in arp.c.

[yanhaowang]

Update according Hiroki advise

1. Use "error" instead of "status" name to store the value of getnameinfo() function.
2. Use compound literals instead of "hints" variable.
3. Check EAI_SYSTEM while using gai_strerror() function.
4. Use sizoef(hostbuf) instead of NI_MAXHOST.

[yanhaowang]

Fix typo and format

[yanhaowang]

Fix getaddr function