struct ifreq : different definition in "linux/if.h" and man page

Question

In online manual page netdevice(7) - Linux man page, the definition of ifreq structure is given as:

struct ifreq {
               char ifr_name[IFNAMSIZ]; /* Interface name */
               union {
                   struct sockaddr ifr_addr;
                   struct sockaddr ifr_dstaddr;
                   struct sockaddr ifr_broadaddr;
                   struct sockaddr ifr_netmask;
                   struct sockaddr ifr_hwaddr;
                   short           ifr_flags;
                   int             ifr_ifindex;
                   int             ifr_metric;
                   int             ifr_mtu;
                   struct ifmap    ifr_map;
                   char            ifr_slave[IFNAMSIZ];
                   char            ifr_newname[IFNAMSIZ];
                   char           *ifr_data;
               };
           };

But my linux header shows different definition. Below is the definition from /usr/include/linux/if.h The kernel version I'm using is Linux 3.18

struct ifreq {
#define IFHWADDRLEN 6
    union
    {
        char    ifrn_name[IFNAMSIZ];        /* if name, e.g. "en0" */
    } ifr_ifrn;

    union {
        struct  sockaddr ifru_addr;
        struct  sockaddr ifru_dstaddr;
        struct  sockaddr ifru_broadaddr;
        struct  sockaddr ifru_netmask;
        struct  sockaddr ifru_hwaddr;
        short   ifru_flags;
        int ifru_ivalue;
        int ifru_mtu;
        struct  ifmap ifru_map;
        char    ifru_slave[IFNAMSIZ];   /* Just fits the size */
        char    ifru_newname[IFNAMSIZ];
        void *  ifru_data;
        struct  if_settings ifru_settings;
    } ifr_ifru;
};

Why is this change made ? Which one should I stick to for portability with different linux distros ?

Solution

Different header files; linux/if.h and net/if.h are similar, but unless you're working against the linux kernel and not the linux userspace, you probably want to use net/if.h.

Comments

[SingerOfTheFall]

That page you linked is almost 2 years old...

[Some programmer dude]

This structure is not mandated by POSIX, it's Linux specific. So if you want portability you can't really use it at all.

[Some programmer dude]

Also, if you look at e.g. /usr/include/net/if.h then you will see that all fields also have aliases by using preprocessing macros, so using just my_ifreq_ptr->ifr_name will automatically be replaced with my_ifreq_ptr->ifr_ifrn.ifrn_name by the preprocessor.

[sergej]

See the git log to find out why this change was made.

[anoop.babu]

@JoachimPileborg, Thanks. I missed the #defines. I came across this confusion while debugging through gnu GDB. Since macros where not applicable in that state, I ran into errors. Now got it !!