Re: [PATCH net-next] net: core: Expose number of link up/down transitions

[Andrei Vagin]

On Thu, Jan 18, 2018 at 01:06:52AM +0100, Andrew Lunn wrote:
> > What is the idea to have two separate counters? Can a delta between them
> > be a bigger than 1?
> 
> Yes, it can.
> 
> These counters are incremented in netif_carrier_on() /
> netif_carrier_off(). They are not always called in pairs and they can
> be called multiple times for the same event. The phylib will call them
> when it notices the PHY saying the link is down/up, and the MAC driver
> sometimes also calls them.

We check the __LINK_STATE_NOCARRIER bit before changing these counters,
so if we call netif_carrier_on() twice, the counter will be incrimented
only by one, will it not?

void netif_carrier_on(struct net_device *dev)
        if (test_and_clear_bit(__LINK_STATE_NOCARRIER, &dev->state)) {
                atomic_inc(&dev->carrier_changes);

...

void netif_carrier_off(struct net_device *dev)
        if (!test_and_set_bit(__LINK_STATE_NOCARRIER, &dev->state)) {
                atomic_inc(&dev->carrier_changes);


> 
> 	  Andrew