As there are multiple ethnl commands that report messages based on
phy_device information, let's introduce a set of ethnl generic dump
helpers to allow DUMP support for each PHY on a given netdev.

This logic iterates over the phy_link_topology of each netdev (or a
single netdev for filtered DUMP), and call ethnl_default_dump_one() with
the req_info populated with ifindex + phyindex.

This allows re-using all the existing infra for phy-targetting commands
that already use ethnl generic helpers.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
V4 : No changes

 net/ethtool/netlink.c | 78 +++++++++++++++++++++++++++++++++++++++++++
 net/ethtool/netlink.h |  6 ++++
 2 files changed, 84 insertions(+)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index 0345bffa0678..171290eaf406 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c

@@ -560,6 +560,84 @@ static int ethnl_default_dump_one(struct sk_buff *skb,
 	return ret;
 }
 
+/* Specific context for phy-targeting command DUMP operatins. We keep in

context
+ * the latest phy_index we dumped, in case of an interrupted DUMP.
+ */
+struct ethnl_dump_ctx_perphy {
+	unsigned long phy_index;
+};
+
+/**
+ * ethnl_dump_start_perphy() - Initialise a dump for PHY cmds
+ * @ctx: Generic ethnl dump context whose cmd_ctx will be initialized
+ *
+ * Initializes a dump context for ethnl commands that may return
+ * one message per PHY on a single netdev.
+ *
+ * Returns: 0 for success, a negative value for errors.