Setting/detecting carrier, and the subsequent implications of setting net_device_ops
ndo_change_carrier
field (if any implications actually exist):
From include/linux/netdevice.h
:
Net device state:
struct net_device { ... snip ... unsigned long state; ... snip ...
State flag bits for later testing:
enum netdev_state_t { __LINK_STATE_START, __LINK_STATE_PRESENT, __LINK_STATE_NOCARRIER, __LINK_STATE_LINKWATCH_PENDING, __LINK_STATE_DORMANT, };
Again from netdevice.h
:
/** * netif_carrier_ok - test if carrier present * @dev: network device * * Check if carrier is present on device */ static inline bool netif_carrier_ok(const struct net_device *dev) { return !test_bit(__LINK_STATE_NOCARRIER, &dev->state); } void netif_carrier_on(struct net_device *dev); void netif_carrier_off(struct net_device *dev);
Still in netdevice.h
:
/** * netif_running - test if up * @dev: network device * * Test if the device has been brought up. */ static inline bool netif_running(const struct net_device *dev) { return test_bit(__LINK_STATE_START, &dev->state); }
From net/sched/sch_generic.c
:
/** * netif_carrier_on - set carrier * @dev: network device * * Device has detected that carrier. */ void netif_carrier_on(struct net_device *dev) { if (test_and_clear_bit(__LINK_STATE_NOCARRIER, &dev->state)) { if (dev->reg_state == NETREG_UNINITIALIZED) return; atomic_inc(&dev->carrier_up_count); linkwatch_fire_event(dev); if (netif_running(dev)) __netdev_watchdog_up(dev); } } EXPORT_SYMBOL(netif_carrier_on); /** * netif_carrier_off - clear carrier * @dev: network device * * Device has detected loss of carrier. */ void netif_carrier_off(struct net_device *dev) { if (!test_and_set_bit(__LINK_STATE_NOCARRIER, &dev->state)) { if (dev->reg_state == NETREG_UNINITIALIZED) return; atomic_inc(&dev->carrier_down_count); linkwatch_fire_event(dev); } } EXPORT_SYMBOL(netif_carrier_off);