net-sysfs: expose number of carrier on/off changes

This allows to monitor carrier on/off transitions and detect link
flapping issues:
 - new /sys/class/net/X/carrier_changes
 - new rtnetlink IFLA_CARRIER_CHANGES (getlink)

Tested:
  - grep . /sys/class/net/*/carrier_changes
    + ip link set dev X down/up
    + plug/unplug cable
  - updated iproute2: prints IFLA_CARRIER_CHANGES
  - iproute2 20121211-2 (debian): unchanged behavior

Signed-off-by: David Decotigny <decot@googlers.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 18 insertions, 1 deletions

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index daed9a64c6f6..462396278484 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -253,6 +253,16 @@ static ssize_t operstate_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(operstate);
 
+static ssize_t carrier_changes_show(struct device *dev,
+                                    struct device_attribute *attr,
+                                    char *buf)
+{
+        struct net_device *netdev = to_net_dev(dev);
+        return sprintf(buf, fmt_dec,
+                       atomic_read(&netdev->carrier_changes));
+}
+static DEVICE_ATTR_RO(carrier_changes);
+
 /* read-write attributes */
 
 static int change_mtu(struct net_device *net, unsigned long new_mtu)
@@ -386,6 +396,7 @@ static struct attribute *net_class_attrs[] = {
         &dev_attr_duplex.attr,
         &dev_attr_dormant.attr,
         &dev_attr_operstate.attr,
+        &dev_attr_carrier_changes.attr,
         &dev_attr_ifalias.attr,
         &dev_attr_carrier.attr,
         &dev_attr_mtu.attr,
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e7c6006bc3ea..d4ff41739b0f 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -822,6 +822,7 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
                + nla_total_size(4) /* IFLA_NUM_RX_QUEUES */
                + nla_total_size(1) /* IFLA_OPERSTATE */
                + nla_total_size(1) /* IFLA_LINKMODE */
+               + nla_total_size(4) /* IFLA_CARRIER_CHANGES */
                + nla_total_size(ext_filter_mask
                                 & RTEXT_FILTER_VF ? 4 : 0) /* IFLA_NUM_VF */
                + rtnl_vfinfo_size(dev, ext_filter_mask) /* IFLA_VFINFO_LIST */
@@ -970,7 +971,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb, struct net_device *dev,
             (dev->qdisc &&
              nla_put_string(skb, IFLA_QDISC, dev->qdisc->ops->id)) ||
             (dev->ifalias &&
-             nla_put_string(skb, IFLA_IFALIAS, dev->ifalias)))
+             nla_put_string(skb, IFLA_IFALIAS, dev->ifalias)) ||
+            nla_put_u32(skb, IFLA_CARRIER_CHANGES,
+                        atomic_read(&dev->carrier_changes)))
                 goto nla_put_failure;
 
         if (1) {
@@ -1147,6 +1150,7 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
         [IFLA_NUM_TX_QUEUES]    = { .type = NLA_U32 },
         [IFLA_NUM_RX_QUEUES]    = { .type = NLA_U32 },
         [IFLA_PHYS_PORT_ID]     = { .type = NLA_BINARY, .len = MAX_PHYS_PORT_ID_LEN },
+        [IFLA_CARRIER_CHANGES]  = { .type = NLA_U32 },  /* ignored */
 };
 
 static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index e82e43b69c33..e1543b03e39d 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -310,6 +310,7 @@ 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_changes);
                 linkwatch_fire_event(dev);
                 if (netif_running(dev))
                         __netdev_watchdog_up(dev);
@@ -328,6 +329,7 @@ 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_changes);
                 linkwatch_fire_event(dev);
         }
 }