net: provide pending ring configuration in net_device

Record the pending configuration in net_device struct.
ethtool core duplicates the current config and the specific
handlers (for now just ringparam) can modify it.

Reviewed-by: Michael Chan <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

include/linux/netdevice.h

@@ -2413,6 +2413,12 @@ struct net_device {
 
 	/** @cfg: net_device queue-related configuration */
 	struct netdev_config	*cfg;
+	/**
+	 * @cfg_pending: same as @cfg but when device is being actively
+	 *	reconfigured includes any changes to the configuration
+	 *	requested by the user, but which may or may not be rejected.
+	 */
+	struct netdev_config	*cfg_pending;
 	struct ethtool_netdev_state *ethtool;
 
 	/* protected by rtnl_lock */

net/core/dev.c

@@ -11546,6 +11546,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 	dev->cfg = kzalloc(sizeof(*dev->cfg), GFP_KERNEL_ACCOUNT);
 	if (!dev->cfg)
 		goto free_all;
+	dev->cfg_pending = dev->cfg;
 
 	napi_config_sz = array_size(maxqs, sizeof(*dev->napi_config));
 	dev->napi_config = kvzalloc(napi_config_sz, GFP_KERNEL_ACCOUNT);
@@ -11615,6 +11616,7 @@ void free_netdev(struct net_device *dev)
 		return;
 	}
 
+	WARN_ON(dev->cfg != dev->cfg_pending);
 	kfree(dev->cfg);
 	kfree(dev->ethtool);
 	netif_free_tx_queues(dev);

net/ethtool/netlink.c

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 
+#include <net/netdev_queues.h>
 #include <net/sock.h>
 #include <linux/ethtool_netlink.h>
 #include <linux/phy_link_topology.h>
@@ -692,19 +693,33 @@ static int ethnl_default_set_doit(struct sk_buff *skb, struct genl_info *info)
 	dev = req_info.dev;
 
 	rtnl_lock();
+	dev->cfg_pending = kmemdup(dev->cfg, sizeof(*dev->cfg),
+				   GFP_KERNEL_ACCOUNT);
+	if (!dev->cfg_pending) {
+		ret = -ENOMEM;
+		goto out_tie_cfg;
+	}
+
 	ret = ethnl_ops_begin(dev);
 	if (ret < 0)
-		goto out_rtnl;
+		goto out_free_cfg;
 
 	ret = ops->set(&req_info, info);
-	if (ret <= 0)
+	if (ret < 0)
+		goto out_ops;
+
+	swap(dev->cfg, dev->cfg_pending);
+	if (!ret)
 		goto out_ops;
 	ethtool_notify(dev, ops->set_ntf_cmd, NULL);
 
 	ret = 0;
 out_ops:
 	ethnl_ops_complete(dev);
-out_rtnl:
+out_free_cfg:
+	kfree(dev->cfg_pending);
+out_tie_cfg:
+	dev->cfg_pending = dev->cfg;
 	rtnl_unlock();
 out_dev:
 	ethnl_parse_header_dev_put(&req_info);

net/ethtool/rings.c

@@ -294,13 +294,11 @@ ethnl_set_rings(struct ethnl_req_info *req_info, struct genl_info *info)
 		return -EINVAL;
 	}
 
+	dev->cfg_pending->hds_config = kernel_ringparam.tcp_data_split;
+	dev->cfg_pending->hds_thresh = kernel_ringparam.hds_thresh;
+
 	ret = dev->ethtool_ops->set_ringparam(dev, &ringparam,
 					      &kernel_ringparam, info->extack);
-	if (!ret) {
-		dev->cfg->hds_config = kernel_ringparam.tcp_data_split;
-		dev->cfg->hds_thresh = kernel_ringparam.hds_thresh;
-	}
-
 	return ret < 0 ? ret : 1;
 }