Differences

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--- operstate [2018/08/26 16:36] – [net/core/net-sysfs.c] rpjday
+++ operstate [2018/08/27 11:07] (current) – [Testing under sysfs] rpjday
@@ Line 66: / Line 66: @@
 ==== include/uapi/linux/if.h ====
+Possible values for ''netdev%%->%%operstate'':
 <code>
@@ Line 116: / Line 118: @@
 ===== Testing under sysfs =====
-Unplugging and plugging:
+Unplugging and plugging (administratively, the interface remains UP the whole time):
 <code>
@@ Line 150: / Line 152: @@
 </code>
-This should be set by ''dev_open()'', so it should be up regardless.
+This should be set by ''dev_open()'', so it should be up regardless. See usage [[https://elixir.bootlin.com/linux/latest/ident/__LINK_STATE_START|here]].
 ==== netif_oper_up() ====
-This is the important one related to plugging and unplugging:
+This is the important one related to plugging and unplugging (ignore the possibility of ''IF_OPER_UNKNOWN'' for now):
 <code>
@@ Line 169: / Line 171: @@
 </code>
 ==== netif_carrier_ok() ====
+This routine becomes important shortly:
 <code>
@@ Line 199: / Line 203: @@
         struct net_device *netdev = to_net_dev(dev);
-        if (netif_running(netdev))  // if IFF_UP, which should be true
+        if (netif_running(netdev))  // if __LINK_STATE_START, which should be true
                 return sprintf(buf, fmt_dec, !!netif_carrier_ok(netdev));
@@ Line 215: / Line 219: @@
 }
 </code>
+==== Where is IF_OPER_DOWN set? ====
+From ''net/core/link_watch.c'', it all comes back to ''netif_carrier_ok()'':
+<code>
+static unsigned char default_operstate(const struct net_device *dev)
+{
+	if (!netif_carrier_ok(dev))
+		return (dev->ifindex != dev_get_iflink(dev) ?
+			IF_OPER_LOWERLAYERDOWN : IF_OPER_DOWN);
+	if (netif_dormant(dev))
+		return IF_OPER_DORMANT;
+	return IF_OPER_UP;
+}
+</code>
+which brings us back to who sets ''%%__%%LINK_STATE_NOCARRIER''.
+==== Setting/detecting carrier ====
+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);
+/**
+ *	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);
+</code>
+So who calls ''netif_carrier_off()''? Apparently, lots of people.