Clarification on rtnetlink requests

Clarification on rtnetlink requests

[David Chappelle]

I am a bit confused with respect to the structure of rtnetlink requests.
It seems that in some circumstances a request can look like:

    struct request
    {
        struct nlmsghdr header;
        struct rtgenmsg body;
    };

and in other cases it can look like:

    struct request
    {
        struct nlmsghdr header;
        struct ifinfomsg body;
    };

How do I know which one to use when sending RTM_GETLINK and
RTM_GETADDR requests? Furthermore, it also seems that 'struct rtattr'
can be specified at the end of the request as well. Is there any
documentation that describes this.

RE: Clarification on rtnetlink requests

[Anish Bhatt]

> -----Original Message-----
> From: netdev-owner@vger.kernel.org [mailto:netdev-
> owner@vger.kernel.org] On Behalf Of David Chappelle
> Sent: Wednesday, August 19, 2015 8:05 AM
> To: netdev@vger.kernel.org
> Subject: Clarification on rtnetlink requests
> 
> I am a bit confused with respect to the structure of rtnetlink requests.
> It seems that in some circumstances a request can look like:
> 
>     struct request
>     {
>         struct nlmsghdr header;
>         struct rtgenmsg body;
>     };
> 
> and in other cases it can look like:
> 
>     struct request
>     {
>         struct nlmsghdr header;
>         struct ifinfomsg body;
>     };
> 
> How do I know which one to use when sending RTM_GETLINK and
> RTM_GETADDR requests? Furthermore, it also seems that 'struct rtattr'
> can be specified at the end of the request as well. Is there any
> documentation that describes this.

RTM_GETLINK uses ifinfomsg and RTM_GETADDR uses ifaddrmsg, see man 7 rtnetlink. struct  rtgenmsg is just a generic type, look at include/linux/rtnetlink.h
-Anish