[PATCH net-next v3 4/6] netpoll: add wrapper around __netpoll_setup with dev reference

[Andre Carvalho <asantostc@gmail.com>]

Introduce __netpoll_setup_hold() which wraps __netpoll_setup() and
on success holds a reference to the device. This helper requires caller
to already hold RNTL and should be paired with netpoll_cleanup to ensure
proper handling of the reference.

This helper is going to be used by netconsole to setup netpoll in
response to a NETDEV_UP event. Since netconsole always perform cleanup
using netpoll_cleanup, this will ensure that reference counting is
correct and handled entirely inside netpoll.

Signed-off-by: Andre Carvalho <asantostc@gmail.com>
---
 include/linux/netpoll.h |  1 +
 net/core/netpoll.c      | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index f22eec466040..345e74112674 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -69,6 +69,7 @@ static inline void netpoll_poll_enable(struct net_device *dev) { return; }
 
 int netpoll_send_udp(struct netpoll *np, const char *msg, int len);
 int __netpoll_setup(struct netpoll *np, struct net_device *ndev);
+int __netpoll_setup_hold(struct netpoll *np, struct net_device *ndev);
 int netpoll_setup(struct netpoll *np);
 void __netpoll_free(struct netpoll *np);
 void netpoll_cleanup(struct netpoll *np);
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index c85f740065fc..4d25ba422d81 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -605,6 +605,26 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
 }
 EXPORT_SYMBOL_GPL(__netpoll_setup);
 
+/*
+ * Wrapper around __netpoll_setup that holds a reference to the device.
+ * The caller must pair this with netpoll_cleanup() to release the reference.
+ */
+int __netpoll_setup_hold(struct netpoll *np, struct net_device *ndev)
+{
+	int err;
+
+	ASSERT_RTNL();
+
+	err = __netpoll_setup(np, ndev);
+	if (err)
+		return err;
+
+	netdev_hold(ndev, &np->dev_tracker, GFP_KERNEL);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(__netpoll_setup_hold);
+
 /*
  * Returns a pointer to a string representation of the identifier used
  * to select the egress interface for the given netpoll instance. buf

-- 
2.51.2