[PATCH v4 3/3] IB/ipoib: Log sysfs 'dev_id' accesses from userspace

[Arseny Maslennikov <ar@cs.msu.ru>]

Some tools may currently be using only the deprecated attribute;
let's print an elaborate and clear deprecation notice to kmsg.

To do that, we have to replace the whole sysfs file, since we inherit
the original one from netdev.

Signed-off-by: Arseny Maslennikov <ar@cs.msu.ru>
---
 drivers/infiniband/ulp/ipoib/ipoib_main.c | 31 +++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index 30f840f874b3..74732726ec6f 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -2386,6 +2386,35 @@ int ipoib_add_pkey_attr(struct net_device *dev)
 	return device_create_file(&dev->dev, &dev_attr_pkey);
 }
 
+/*
+ * We erroneously exposed the iface's port number in the dev_id
+ * sysfs field long after dev_port was introduced for that purpose[1],
+ * and we need to stop everyone from relying on that.
+ * Let's overload the shower routine for the dev_id file here
+ * to gently bring the issue up.
+ *
+ * [1] https://www.spinics.net/lists/netdev/msg272123.html
+ */
+static ssize_t dev_id_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct net_device *ndev = to_net_dev(dev);
+
+	if (ndev->dev_id == ndev->dev_port)
+		netdev_info_once(ndev,
+			"\"%s\" wants to know my dev_id. Should it look at dev_port instead? See Documentation/ABI/testing/sysfs-class-net for more info.\n",
+			current->comm);
+
+	return sprintf(buf, "%#x\n", ndev->dev_id);
+}
+static DEVICE_ATTR_RO(dev_id);
+
+int ipoib_intercept_dev_id_attr(struct net_device *dev)
+{
+	device_remove_file(&dev->dev, &dev_attr_dev_id);
+	return device_create_file(&dev->dev, &dev_attr_dev_id);
+}
+
 static struct net_device *ipoib_add_port(const char *format,
 					 struct ib_device *hca, u8 port)
 {
@@ -2427,6 +2456,8 @@ static struct net_device *ipoib_add_port(const char *format,
 	 */
 	ndev->priv_destructor = ipoib_intf_free;
 
+	if (ipoib_intercept_dev_id_attr(ndev))
+		goto sysfs_failed;
 	if (ipoib_cm_add_mode_attr(ndev))
 		goto sysfs_failed;
 	if (ipoib_add_pkey_attr(ndev))
-- 
2.19.0.rc2