[PATCH net-next v3 1/7] net: ethtool: netlink: Allow per-netdevice DUMP operations

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

We have a number of netlink commands in the ethnl family that may have
multiple objects to dump even for a single net_device, including :

 - PLCA, PSE-PD, phy: one message per PHY device
 - tsinfo: one message per timestamp source (netdev + phys)
 - rss: One per RSS context

To get this behaviour, these netlink commands need to roll a custom
->dumpit().

To prepare making per-netdev DUMP more generic in ethnl, introduce a
member in the ethnl ops to indicate if a given command may allow
pernetdev DUMPs (also referred to as filtered DUMPs).

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 net/ethtool/netlink.c | 45 +++++++++++++++++++++++++++++--------------
 net/ethtool/netlink.h |  2 ++
 2 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index a163d40c6431..7adede5e4ff1 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -587,21 +587,38 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
 	int ret = 0;
 
 	rcu_read_lock();
-	for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
-		dev_hold(dev);
+	if (ctx->req_info->dev) {
+		dev = ctx->req_info->dev;
 		rcu_read_unlock();
+		/* Filtered DUMP request targeted to a single netdev. We already
+		 * hold a ref to the netdev from ->start()
+		 */
+		ret = ethnl_default_dump_one(skb, dev, ctx,
+					     genl_info_dump(cb));
+		rcu_read_lock();
+		netdev_put(ctx->req_info->dev, &ctx->req_info->dev_tracker);
 
-		ret = ethnl_default_dump_one(skb, dev, ctx, genl_info_dump(cb));
+		if (ret < 0 && ret != -EOPNOTSUPP && likely(skb->len))
+			ret = skb->len;
 
-		rcu_read_lock();
-		dev_put(dev);
+	} else {
+		for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
+			dev_hold(dev);
+			rcu_read_unlock();
+
+			ret = ethnl_default_dump_one(skb, dev, ctx,
+						     genl_info_dump(cb));
+
+			rcu_read_lock();
+			dev_put(dev);
 
-		if (ret < 0 && ret != -EOPNOTSUPP) {
-			if (likely(skb->len))
-				ret = skb->len;
-			break;
+			if (ret < 0 && ret != -EOPNOTSUPP) {
+				if (likely(skb->len))
+					ret = skb->len;
+				break;
+			}
+			ret = 0;
 		}
-		ret = 0;
 	}
 	rcu_read_unlock();
 
@@ -635,10 +652,10 @@ static int ethnl_default_start(struct netlink_callback *cb)
 	}
 
 	ret = ethnl_default_parse(req_info, &info->info, ops, false);
-	if (req_info->dev) {
-		/* We ignore device specification in dump requests but as the
-		 * same parser as for non-dump (doit) requests is used, it
-		 * would take reference to the device if it finds one
+	if (req_info->dev && !ops->allow_pernetdev_dump) {
+		/* We ignore device specification in unfiltered dump requests
+		 * but as the same parser as for non-dump (doit) requests is
+		 * used, it would take reference to the device if it finds one
 		 */
 		netdev_put(req_info->dev, &req_info->dev_tracker);
 		req_info->dev = NULL;
diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
index ec6ab5443a6f..4aaa73282d6a 100644
--- a/net/ethtool/netlink.h
+++ b/net/ethtool/netlink.h
@@ -331,6 +331,7 @@ int ethnl_sock_priv_set(struct sk_buff *skb, struct net_device *dev, u32 portid,
  * @req_info_size:    size of request info
  * @reply_data_size:  size of reply data
  * @allow_nodev_do:   allow non-dump request with no device identification
+ * @allow_pernetdev_dump: allow filtering dump requests with ifname/ifindex
  * @set_ntf_cmd:      notification to generate on changes (SET)
  * @parse_request:
  *	Parse request except common header (struct ethnl_req_info). Common
@@ -388,6 +389,7 @@ struct ethnl_request_ops {
 	unsigned int		req_info_size;
 	unsigned int		reply_data_size;
 	bool			allow_nodev_do;
+	bool			allow_pernetdev_dump;
 	u8			set_ntf_cmd;
 
 	int (*parse_request)(struct ethnl_req_info *req_info,
-- 
2.48.1