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--- ndo_change_carrier [2018/08/04 10:24] – rpjday
+++ ndo_change_carrier [2018/08/04 17:31] (current) – [Overview] rpjday
@@ Line 1: / Line 1: @@
 ===== Overview =====
-The implications of setting ''net_device_ops'' ''ndo_change_carrier'' field.
+Setting/detecting carrier, and the subsequent implications of setting ''net_device_ops'' ''ndo_change_carrier'' field (if any implications actually exist):
-===== net/core/net-sysfs.c =====
+===== Normal behaviour =====
+==== Net device state ====
+From ''include/linux/netdevice.h'':
+Net device state:
 <code>
-static int change_carrier(struct net_device *dev, unsigned long new_carrier)
+struct net_device {
+        ... snip ...
+        unsigned long           state;
+        ... snip ...
+</code>
+State flag bits for later testing:
+<code>
+enum netdev_state_t {
+        __LINK_STATE_START,
+        __LINK_STATE_PRESENT,
+        __LINK_STATE_NOCARRIER,
+        __LINK_STATE_LINKWATCH_PENDING,
+        __LINK_STATE_DORMANT,
+};
+</code>
+==== Checking for state of carrier ====
+Again from ''netdevice.h'':
+<code>
+/**
+ *      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)
 {
-        if (!netif_running(dev))
+        return !test_bit(__LINK_STATE_NOCARRIER, &dev->state);
-                return -EINVAL;
-        return dev_change_carrier(dev, (bool) new_carrier);
 }
-static ssize_t carrier_store(struct device *dev, struct device_attribute *attr,
+void netif_carrier_on(struct net_device *dev);
-                             const char *buf, size_t len)
+void netif_carrier_off(struct net_device *dev);
+</code>
+==== Test for interface running ====
+Still in ''netdevice.h'':
+<code>
+/**
+ *	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 netdev_store(dev, attr, buf, len, change_carrier);
+	return test_bit(__LINK_STATE_START, &dev->state);
+}
+</code>
+==== Test if carrier on or off ====
+From ''net/sched/sch_generic.c'':
+<code>
+/**
+ *      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);
-static ssize_t carrier_show(struct device *dev,
+/**
-                            struct device_attribute *attr, char *buf)
+ *      netif_carrier_off - clear carrier
+ *      @dev: network device
+ *
+ * Device has detected loss of carrier.
+ */
+void netif_carrier_off(struct net_device *dev)
 {
-        struct net_device *netdev = to_net_dev(dev);
+        if (!test_and_set_bit(__LINK_STATE_NOCARRIER, &dev->state)) {
-        if (netif_running(netdev)) {
+                if (dev->reg_state == NETREG_UNINITIALIZED)
-                return sprintf(buf, fmt_dec, !!netif_carrier_ok(netdev));
+                        return;
+                atomic_inc(&dev->carrier_down_count);
+                linkwatch_fire_event(dev);
         }
-        return -EINVAL;
 }
-static DEVICE_ATTR_RW(carrier);
+EXPORT_SYMBOL(netif_carrier_off);
 </code>