Re: RtNetlink in wireless.c and netlink_broadcast(uevent_sock,...) - newbie

[Jean Tourrilhes <jt@hpl.hp.com>]

Xu Nakajima wrote :
> 
> Hello,
> 
> I saw that in the wireless linux stack, there is usage
> 
> of sending messages to user space via the RtNetlink
> event channel : 
> in net/core/wireless.c,  wireless_send_event() method
> calls rtmsg_iwinfo() which calls
> netlink_broadcast(rtnl, skb, 0, RTNLGRP_LINK,
> GFP_ATOMIC); (it fills a struct with 
> rtnetlink_fill_iwinfo before).
> 
> On the other hand, I see that for example, in the case
> of 
> sending messeges to userspace udev socket, the
> netlink_broadcast() call is with a different
> mecahinsm;  
> In lib/kobject_uevent.c, there is the following call
> netlink_broadcast(uevent_sock, skb, 0, 1, GFP_KERNEL);
> 
> Is there something special about RtNetlink event
> channel
> which makes it needed fot wireless.c (for example)? 
> While udev can use some other mechanism ?
> What is special about RtNetlink event channel
> in comaprison to non RtNetlink channels?

	Netlink is a generic socket mechanism. On top of Netlink, you
can have multiple types of sockets, the same way that on top of TCP
sockets you can implement various protocols, such as HTTP, NFS, SSH...
	RtNetlink was the first Netlink protocol implemented and is
the Netlink protocol used to configure network interfaces. In the file
net/core/rtnetlink.c, you will find that there are many actions that
generates RtNetlink events. Together with wireless events, they give
you a very detailed view of what's happening with network interfaces.
	The udev-netlink protocol is quite recent and a completely
different Netlink ptotocol that uses a different packet format. As far
as exporting network information, it is very crude, because the goal
of udev is not managing network interfaces. Yes, udev does duplicate
some RtNetlink events, but the overlap is not so much, so that's ok.

	Good luck...

	Jean