[RFC PATCH 4/4] mpls: use typed fields for per-device sysctls

[Alexey Gladkov <legion@kernel.org>]

MPLS clones its device sysctl table and converts relative data pointers
into mpls_dev addresses at registration time. It also stores the device
and network namespace in extra1 and extra2 for the handler.

Use a context wrapper to retain both objects and select mpls_dev as the
backing object for typed field offsets. The static field table can then
be shared by all devices without allocating and rewriting a ctl_table
array.

Signed-off-by: Alexey Gladkov <legion@kernel.org>
---
 net/mpls/af_mpls.c | 66 ++++++++++++++++++++++------------------------
 1 file changed, 31 insertions(+), 35 deletions(-)

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 26340a7306b5..725df199cf1d 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -1387,8 +1387,18 @@ static int mpls_netconf_dump_devconf(struct sk_buff *skb,
 	return err;
 }
 
-#define MPLS_PERDEV_SYSCTL_OFFSET(field)	\
-	(&((struct mpls_dev *)0)->field)
+struct mpls_dev_sysctl_context {
+	struct sysctl_context context;
+	struct mpls_dev *mdev;
+};
+
+static void *mpls_dev_sysctl_object(const struct sysctl_context *ctx)
+{
+	const struct mpls_dev_sysctl_context *mpls_ctx;
+
+	mpls_ctx = container_of(ctx, struct mpls_dev_sysctl_context, context);
+	return mpls_ctx->mdev;
+}
 
 static int mpls_conf_proc(const struct ctl_table *ctl, int write,
 			  void *buffer, size_t *lenp, loff_t *ppos)
@@ -1397,14 +1407,12 @@ static int mpls_conf_proc(const struct ctl_table *ctl, int write,
 	int ret = proc_dointvec(ctl, write, buffer, lenp, ppos);
 
 	if (write) {
-		struct mpls_dev *mdev = ctl->extra1;
-		int i = (int *)ctl->data - (int *)mdev;
-		struct net *net = ctl->extra2;
+		struct mpls_dev *mdev;
 		int val = *(int *)ctl->data;
 
-		if (i == offsetof(struct mpls_dev, input_enabled) &&
-		    val != oval) {
-			mpls_netconf_notify_devconf(net, RTM_NEWNETCONF,
+		mdev = container_of(ctl->data, struct mpls_dev, input_enabled);
+		if (val != oval) {
+			mpls_netconf_notify_devconf(dev_net(mdev->dev), RTM_NEWNETCONF,
 						    NETCONFA_INPUT, mdev);
 		}
 	}
@@ -1412,13 +1420,13 @@ static int mpls_conf_proc(const struct ctl_table *ctl, int write,
 	return ret;
 }
 
-static const struct ctl_table mpls_dev_table[] = {
+static const struct sysctl_field mpls_dev_table[] = {
 	{
 		.procname	= "input",
-		.maxlen		= sizeof(int),
 		.mode		= 0644,
+		.type		= SYSCTL_FIELD_INT,
 		.proc_handler	= mpls_conf_proc,
-		.data		= MPLS_PERDEV_SYSCTL_OFFSET(input_enabled),
+		.data_offset	= SYSCTL_FIELD_INT_OFFSET(struct mpls_dev, input_enabled),
 	},
 };
 
@@ -1426,35 +1434,27 @@ static int mpls_dev_sysctl_register(struct net_device *dev,
 				    struct mpls_dev *mdev)
 {
 	char path[sizeof("net/mpls/conf/") + IFNAMSIZ];
-	size_t table_size = ARRAY_SIZE(mpls_dev_table);
 	struct net *net = dev_net(dev);
-	struct ctl_table *table;
-	int i;
-
-	table = kmemdup(&mpls_dev_table, sizeof(mpls_dev_table), GFP_KERNEL);
-	if (!table)
-		goto out;
-
-	/* Table data contains only offsets relative to the base of
-	 * the mdev at this point, so make them absolute.
-	 */
-	for (i = 0; i < table_size; i++) {
-		table[i].data = (char *)mdev + (uintptr_t)table[i].data;
-		table[i].extra1 = mdev;
-		table[i].extra2 = net;
-	}
+	struct mpls_dev_sysctl_context ctx = {
+		.context = {
+			.object_size = sizeof(*mdev),
+			.object = mpls_dev_sysctl_object,
+		},
+		.mdev = mdev,
+	};
 
 	snprintf(path, sizeof(path), "net/mpls/conf/%s", dev->name);
 
-	mdev->sysctl = register_net_sysctl_sz(net, path, table, table_size);
+	mdev->sysctl =
+		__register_sysctl_fields(&net->sysctls, path, mpls_dev_table,
+					 ARRAY_SIZE(mpls_dev_table), &ctx.context,
+					 sizeof(ctx));
 	if (!mdev->sysctl)
-		goto free;
+		goto out;
 
 	mpls_netconf_notify_devconf(net, RTM_NEWNETCONF, NETCONFA_ALL, mdev);
 	return 0;
 
-free:
-	kfree(table);
 out:
 	mdev->sysctl = NULL;
 	return -ENOBUFS;
@@ -1464,14 +1464,10 @@ static void mpls_dev_sysctl_unregister(struct net_device *dev,
 				       struct mpls_dev *mdev)
 {
 	struct net *net = dev_net(dev);
-	const struct ctl_table *table;
-
 	if (!mdev->sysctl)
 		return;
 
-	table = mdev->sysctl->ctl_table_arg;
 	unregister_net_sysctl_table(mdev->sysctl);
-	kfree(table);
 
 	mpls_netconf_notify_devconf(net, RTM_DELNETCONF, 0, mdev);
 }
-- 
2.55.0