Documentation: bring operstate documentation up-to-date

2. Querying from userspace

Both admin and operational state can be queried via the netlink

operation RTM_GETLINK. It is also possible to subscribe to RTMGRP_LINK

to be notified of updates. This is important for setting from userspace.

operation RTM_GETLINK. It is also possible to subscribe to RTNLGRP_LINK

to be notified of updates while the interface is admin up. This is

important for setting from userspace.

These values contain interface state:

complete. Corresponding functions are netif_dormant_on() to set the

flag, netif_dormant_off() to clear it and netif_dormant() to query.

On device allocation, networking core sets the flags equivalent to

netif_carrier_ok() and !netif_dormant().

On device allocation, both flags __LINK_STATE_NOCARRIER and

__LINK_STATE_DORMANT are cleared, so the effective state is equivalent

to netif_carrier_ok() and !netif_dormant().

Whenever the driver CHANGES one of these flags, a workqueue event is

driver. Afterwards, the userspace application can set IFLA_OPERSTATE

to IF_OPER_DORMANT or IF_OPER_UP as long as the driver does not set

netif_carrier_off() or netif_dormant_on(). Changes made by userspace

are multicasted on the netlink group RTMGRP_LINK.

are multicasted on the netlink group RTNLGRP_LINK.

So basically a 802.1X supplicant interacts with the kernel like this:

-subscribe to RTMGRP_LINK

-subscribe to RTNLGRP_LINK

-set IFLA_LINKMODE to 1 via RTM_SETLINK

-query RTM_GETLINK once to get initial state

-if initial flags are not (IFF_LOWER_UP && !IFF_DORMANT), wait until

 *	netif_carrier_on - set carrier

 *	@dev: network device

 *

 * Device has detected that carrier.

 * Device has detected acquisition of carrier.

 */

void netif_carrier_on(struct net_device *dev)

{