[PATCH net-next v4 2/8] 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>
---
V4: - Don't hold RCU in the filtered path
    - Move dump_all into a new separate helper

 net/ethtool/netlink.c | 37 ++++++++++++++++++++++++++++++-------
 net/ethtool/netlink.h |  2 ++
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index 6b1725795435..31ab89ca0bcc 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -577,9 +577,7 @@ static int ethnl_default_dump_one(struct sk_buff *skb, struct net_device *dev,
 	return ret;
 }
 
-/* Default ->dumpit() handler for GET requests. */
-static int ethnl_default_dumpit(struct sk_buff *skb,
-				struct netlink_callback *cb)
+static int ethnl_dump_all(struct sk_buff *skb, struct netlink_callback *cb)
 {
 	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
 	struct net *net = sock_net(skb->sk);
@@ -609,6 +607,31 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
 	return ret;
 }
 
+/* Default ->dumpit() handler for GET requests. */
+static int ethnl_default_dumpit(struct sk_buff *skb,
+				struct netlink_callback *cb)
+{
+	struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
+	int ret;
+
+	if (ctx->req_info->dev) {
+		/* Filtered DUMP request targeted to a single netdev. We already
+		 * hold a ref to the netdev from ->start()
+		 */
+		ret = ethnl_default_dump_one(skb, ctx->req_info->dev, ctx,
+					     genl_info_dump(cb));
+		netdev_put(ctx->req_info->dev, &ctx->req_info->dev_tracker);
+
+		if (ret < 0 && ret != -EOPNOTSUPP && likely(skb->len))
+			ret = skb->len;
+
+	} else {
+		ret = ethnl_dump_all(skb, cb);
+	}
+
+	return ret;
+}
+
 /* generic ->start() handler for GET requests */
 static int ethnl_default_start(struct netlink_callback *cb)
 {
@@ -636,10 +659,10 @@ 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