rtnetlink: add ndo_fdb_dump_context

rtnl_fdb_dump() and various ndo_fdb_dump() helpers share
a hidden layout of cb->ctx.

Before switching rtnl_fdb_dump() to for_each_netdev_dump()
in the following patch, make this more explicit.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241209100747.2269613-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

7 files changed, 32 insertions, 18 deletions

diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
index a293b08f36d4..147a93bf9fa9 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
@@ -780,13 +780,14 @@ struct ethsw_dump_ctx {
 static int dpaa2_switch_fdb_dump_nl(struct fdb_dump_entry *entry,
 				    struct ethsw_dump_ctx *dump)
 {
+	struct ndo_fdb_dump_context *ctx = (void *)dump->cb->ctx;
 	int is_dynamic = entry->type & DPSW_FDB_ENTRY_DINAMIC;
 	u32 portid = NETLINK_CB(dump->cb->skb).portid;
 	u32 seq = dump->cb->nlh->nlmsg_seq;
 	struct nlmsghdr *nlh;
 	struct ndmsg *ndm;
 
-	if (dump->idx < dump->cb->args[2])
+	if (dump->idx < ctx->fdb_idx)
 		goto skip;
 
 	nlh = nlmsg_put(dump->skb, portid, seq, RTM_NEWNEIGH,
diff --git a/drivers/net/ethernet/mscc/ocelot_net.c b/drivers/net/ethernet/mscc/ocelot_net.c
index 558e03301aa8..8d48468cddd7 100644
--- a/drivers/net/ethernet/mscc/ocelot_net.c
+++ b/drivers/net/ethernet/mscc/ocelot_net.c
@@ -758,12 +758,13 @@ static int ocelot_port_fdb_do_dump(const unsigned char *addr, u16 vid,
 				   bool is_static, void *data)
 {
 	struct ocelot_dump_ctx *dump = data;
+	struct ndo_fdb_dump_context *ctx = (void *)dump->cb->ctx;
 	u32 portid = NETLINK_CB(dump->cb->skb).portid;
 	u32 seq = dump->cb->nlh->nlmsg_seq;
 	struct nlmsghdr *nlh;
 	struct ndmsg *ndm;
 
-	if (dump->idx < dump->cb->args[2])
+	if (dump->idx < ctx->fdb_idx)
 		goto skip;
 
 	nlh = nlmsg_put(dump->skb, portid, seq, RTM_NEWNEIGH,
diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 43cf672b7b9f..0c356e0a61ef 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -1352,6 +1352,7 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
 			  struct net_device *dev,
 			  struct net_device *filter_dev, int *idx)
 {
+	struct ndo_fdb_dump_context *ctx = (void *)cb->ctx;
 	struct vxlan_dev *vxlan = netdev_priv(dev);
 	unsigned int h;
 	int err = 0;
@@ -1364,7 +1365,7 @@ static int vxlan_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb,
 			struct vxlan_rdst *rd;
 
 			if (rcu_access_pointer(f->nh)) {
-				if (*idx < cb->args[2])
+				if (*idx < ctx->fdb_idx)
 					goto skip_nh;
 				err = vxlan_fdb_info(skb, vxlan, f,
 						     NETLINK_CB(cb->skb).portid,
@@ -1381,7 +1382,7 @@ skip_nh:
 			}
 
 			list_for_each_entry_rcu(rd, &f->remotes, list) {
-				if (*idx < cb->args[2])
+				if (*idx < ctx->fdb_idx)
 					goto skip;
 
 				err = vxlan_fdb_info(skb, vxlan, f,
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 811ce44113f6..c43cffb014a7 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -178,6 +178,13 @@ void rtnetlink_init(void);
 void __rtnl_unlock(void);
 void rtnl_kfree_skbs(struct sk_buff *head, struct sk_buff *tail);
 
+/* Shared by rtnl_fdb_dump() and various ndo_fdb_dump() helpers. */
+struct ndo_fdb_dump_context {
+	unsigned long s_h;
+	unsigned long s_idx;
+	unsigned long fdb_idx;
+};
+
 extern int ndo_dflt_fdb_dump(struct sk_buff *skb,
 			     struct netlink_callback *cb,
 			     struct net_device *dev,
diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 82bac2426631..902694c0ce64 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -955,6 +955,7 @@ int br_fdb_dump(struct sk_buff *skb,
 		struct net_device *filter_dev,
 		int *idx)
 {
+	struct ndo_fdb_dump_context *ctx = (void *)cb->ctx;
 	struct net_bridge *br = netdev_priv(dev);
 	struct net_bridge_fdb_entry *f;
 	int err = 0;
@@ -970,7 +971,7 @@ int br_fdb_dump(struct sk_buff *skb,
 
 	rcu_read_lock();
 	hlist_for_each_entry_rcu(f, &br->fdb_list, fdb_node) {
-		if (*idx < cb->args[2])
+		if (*idx < ctx->fdb_idx)
 			goto skip;
 		if (filter_dev && (!f->dst || f->dst->dev != filter_dev)) {
 			if (filter_dev != dev)
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index ab5f201bf0ab..453cc8bf18fb 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -4762,15 +4762,16 @@ static int nlmsg_populate_fdb(struct sk_buff *skb,
 			      int *idx,
 			      struct netdev_hw_addr_list *list)
 {
+	struct ndo_fdb_dump_context *ctx = (void *)cb->ctx;
 	struct netdev_hw_addr *ha;
-	int err;
 	u32 portid, seq;
+	int err;
 
 	portid = NETLINK_CB(cb->skb).portid;
 	seq = cb->nlh->nlmsg_seq;
 
 	list_for_each_entry(ha, &list->list, list) {
-		if (*idx < cb->args[2])
+		if (*idx < ctx->fdb_idx)
 			goto skip;
 
 		err = nlmsg_populate_fdb_fill(skb, dev, ha->addr, 0,
@@ -4909,10 +4910,9 @@ static int valid_fdb_dump_legacy(const struct nlmsghdr *nlh,
 
 static int rtnl_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 {
-	struct net_device *dev;
-	struct net_device *br_dev = NULL;
-	const struct net_device_ops *ops = NULL;
-	const struct net_device_ops *cops = NULL;
+	const struct net_device_ops *ops = NULL, *cops = NULL;
+	struct ndo_fdb_dump_context *ctx = (void *)cb->ctx;
+	struct net_device *dev, *br_dev = NULL;
 	struct net *net = sock_net(skb->sk);
 	struct hlist_head *head;
 	int brport_idx = 0;
@@ -4922,6 +4922,8 @@ static int rtnl_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 	int err = 0;
 	int fidx = 0;
 
+	NL_ASSERT_CTX_FITS(struct ndo_fdb_dump_context);
+
 	if (cb->strict_check)
 		err = valid_fdb_dump_strict(cb->nlh, &br_idx, &brport_idx,
 					    cb->extack);
@@ -4939,8 +4941,8 @@ static int rtnl_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 		ops = br_dev->netdev_ops;
 	}
 
-	s_h = cb->args[0];
-	s_idx = cb->args[1];
+	s_h = ctx->s_h;
+	s_idx = ctx->s_idx;
 
 	for (h = s_h; h < NETDEV_HASHENTRIES; h++, s_idx = 0) {
 		idx = 0;
@@ -4992,7 +4994,7 @@ static int rtnl_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb)
 			cops = NULL;
 
 			/* reset fdb offset to 0 for rest of the interfaces */
-			cb->args[2] = 0;
+			ctx->fdb_idx = 0;
 			fidx = 0;
 cont:
 			idx++;
@@ -5000,9 +5002,9 @@ cont:
 	}
 
 out:
-	cb->args[0] = h;
-	cb->args[1] = idx;
-	cb->args[2] = fidx;
+	ctx->s_h = h;
+	ctx->s_idx = idx;
+	ctx->fdb_idx = fidx;
 
 	return skb->len;
 }
diff --git a/net/dsa/user.c b/net/dsa/user.c
index 06c30a9e29ff..c736c019e2af 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -515,12 +515,13 @@ dsa_user_port_fdb_do_dump(const unsigned char *addr, u16 vid,
 			  bool is_static, void *data)
 {
 	struct dsa_user_dump_ctx *dump = data;
+	struct ndo_fdb_dump_context *ctx = (void *)dump->cb->ctx;
 	u32 portid = NETLINK_CB(dump->cb->skb).portid;
 	u32 seq = dump->cb->nlh->nlmsg_seq;
 	struct nlmsghdr *nlh;
 	struct ndmsg *ndm;
 
-	if (dump->idx < dump->cb->args[2])
+	if (dump->idx < ctx->fdb_idx)
 		goto skip;
 
 	nlh = nlmsg_put(dump->skb, portid, seq, RTM_NEWNEIGH,