[PATCH net-next v2 5/6] netconsole: resume previously deactivated target

[Andre Carvalho <asantostc@gmail.com>]

Attempt to resume a previously deactivated target when the associated
interface comes back (NETDEV_UP event is received) by calling
__netpoll_setup_hold on the device.

For targets that were initally setup by mac address, their address is
also compared with the interface address (while still verifying that the
interface name matches).

__netpoll_setup_hold assumes RTNL is held (which is guaranteed to be the
case when handling the event) and holds a reference to the device in
case of success. This reference will be removed upon target (or
netconsole) removal by netpoll_cleanup.

Target transitions to STATE_DISABLED in case of failures resuming it to
avoid retrying the same target indefinitely.

Signed-off-by: Andre Carvalho <asantostc@gmail.com>
---
 drivers/net/netconsole.c | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 59d770bb4baa5f9616b10c0dfb39ed45a4eb7710..96485e979e61e0ed6c850ae3b29f46d529923f2d 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -135,10 +135,12 @@ enum target_state {
  * @stats:	Packet send stats for the target. Used for debugging.
  * @state:	State of the target.
  *		Visible from userspace (read-write).
- *		We maintain a strict 1:1 correspondence between this and
- *		whether the corresponding netpoll is active or inactive.
+ *		From a userspace perspective, the target is either enabled or
+ *		disabled. Internally, although both STATE_DISABLED and
+ *		STATE_DEACTIVATED correspond to inactive netpoll the latter is
+ *		due to interface state changes and may recover automatically.
  *		Also, other parameters of a target may be modified at
- *		runtime only when it is disabled (state == STATE_DISABLED).
+ *		runtime only when it is disabled (state != STATE_ENABLED).
  * @extended:	Denotes whether console is extended or not.
  * @release:	Denotes whether kernel release version should be prepended
  *		to the message. Depends on extended console.
@@ -1430,6 +1432,31 @@ static int prepare_extradata(struct netconsole_target *nt)
 }
 #endif	/* CONFIG_NETCONSOLE_DYNAMIC */
 
+/* Attempts to resume logging to a deactivated target. */
+static void maybe_resume_target(struct netconsole_target *nt,
+				struct net_device *ndev)
+{
+	int ret;
+
+	if (strncmp(nt->np.dev_name, ndev->name, IFNAMSIZ))
+		return;
+
+	/* for targets specified by mac, also verify it matches the addr */
+	if (!is_broadcast_ether_addr(nt->np.dev_mac) &&
+	    memcmp(nt->np.dev_mac, ndev->dev_addr, ETH_ALEN))
+		return;
+
+	ret = __netpoll_setup_hold(&nt->np, ndev);
+	if (ret) {
+		/* netpoll fails setup once, do not try again. */
+		nt->state = STATE_DISABLED;
+	} else {
+		nt->state = STATE_ENABLED;
+		pr_info("network logging resumed on interface %s\n",
+			nt->np.dev_name);
+	}
+}
+
 /* Handle network interface device notifications */
 static int netconsole_netdev_event(struct notifier_block *this,
 				   unsigned long event, void *ptr)
@@ -1440,7 +1467,8 @@ static int netconsole_netdev_event(struct notifier_block *this,
 	bool stopped = false;
 
 	if (!(event == NETDEV_CHANGENAME || event == NETDEV_UNREGISTER ||
-	      event == NETDEV_RELEASE || event == NETDEV_JOIN))
+	      event == NETDEV_RELEASE || event == NETDEV_JOIN ||
+	      event == NETDEV_UP))
 		goto done;
 
 	mutex_lock(&target_cleanup_list_lock);
@@ -1460,6 +1488,8 @@ static int netconsole_netdev_event(struct notifier_block *this,
 				stopped = true;
 			}
 		}
+		if (nt->state == STATE_DEACTIVATED && event == NETDEV_UP)
+			maybe_resume_target(nt, dev);
 		netconsole_target_put(nt);
 	}
 	spin_unlock_irqrestore(&target_list_lock, flags);

-- 
2.51.0