Add: netlink socket options

[Ignatella]

Hi!

While using nftables we understood that it would be great to be able to set some options on the socket, i.e. setting r/w buffer size or pid retrieval to track what process issues rule changes.

This PR attemps to add such api to the New method through options (callbacks) executed every time dialNetlink called.

[stapelberg]

While using nftables we understood that it would be great to be able to set some options on the socket, i.e. setting r/w buffer size or pid retrieval to track what process issues rule changes.

Out of curiosity: Under which conditions do you need to adjust the r/w buffer size?

Is the code which sets the options open source? If so, can you share a link please?

[Ignatella]

@stapelberg

Out of curiosity: Under which conditions do you need to adjust the r/w buffer size?

One of the flows and assumptions we must consider is the ability to set up to 5,000 rules in a single transaction. However, using the default buffer sizes causes the process to get stuck indefinitely.

conn, err: = nftables.New(nftables.WithSockOptions(func(conn * netlink.Conn) error {
    // 20 mb for read and write buffer
    if err: = conn.SetReadBuffer(20971520);
    err != nil {
        return err
    }

    if err: = conn.SetWriteBuffer(20971520);
    err != nil {
        return err
    }

    pid, err: = getPortID(conn)

    if err != nil {
        return err
    }

    nftportid.SetNftablesPortID(pid)

    return nil
}))

func getPortID(conn * netlink.Conn)(uint32, error) {
    var (
        sa unix.Sockaddr err error
    )
    rawConn, err: = conn.SyscallConn()
    if err != nil {
        return 0, err
    }
    doErr: = rawConn.Control(func(fd uintptr) {
        for {
            sa, err = unix.Getsockname(int(fd))
            if ready(err) {
                return
            }
        }
    })
    if doErr != nil {
        return 0, doErr
    }
    if err != nil {
        return 0, err
    }
    saCast, ok: = sa.( * unix.SockaddrNetlink)
    if !ok {
        return 0, errors.New("SockaddrNetlink missing? should not happen")
    }
    return saCast.Pid, nil
}

The code is not open source, but we can share how we use the proposed functionality. 😊 Also, please note the 'port ID' part, which we use to track who issues the changes.