netdev - [PATCH net] net: ethtool: Set the req_info->dev on DUMP requests for each dev

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Message-ID: <20250302162137.698092-1-maxime.chevallier@bootlin.com>
Date: Sun,  2 Mar 2025 17:21:36 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: davem@...emloft.net,
	Andrew Lunn <andrew@...n.ch>,
	Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Heiner Kallweit <hkallweit1@...il.com>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	thomas.petazzoni@...tlin.com,
	linux-arm-kernel@...ts.infradead.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Herve Codina <herve.codina@...tlin.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Köry Maincent <kory.maincent@...tlin.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Simon Horman <horms@...nel.org>,
	Romain Gantois <romain.gantois@...tlin.com>,
	Piergiorgio Beruto <piergiorgio.beruto@...il.com>
Subject: [PATCH net] net: ethtool: Set the req_info->dev on DUMP requests for each dev

There are a few netlink commands that rely on the req_info->dev field
being populated by ethnl in their ->prepare_data() and ->fill_reply().

For a regular GET request, this will be set by ethnl_default_parse(),
which calls ethnl_parse_header_dev_get().

In the case of a DUMP request, the ->prepare_data() and ->fill_reply()
callbacks will be called with the req_info->dev being NULL, which can
cause discrepancies in the behaviour between GET and DUMP results.

The main impact is that ethnl_req_get_phydev() will not find any
phy_device, impacting :
 - plca
 - pse-pd
 - stats

Some other commands rely on req_info->dev, namely :
 - coalesce in ->fill_reply to look for an irq_moder

Although cable_test and tunnels also rely on req_info->dev being set,
that's not a problem for these commands as :
 - cable_test doesn't support DUMP
 - tunnels rolls its own ->dumpit (and sets dev in the req_info).
 - phy also has its own ->dumpit

All other commands use reply_data->dev (probably the correct way of
doing things) and aren't facing this issue.

Simply set the dev in the req_info context when iterating to dump each
dev.

Fixes: c15e065b46dc ("net: ethtool: Allow passing a phy index for some commands")
Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
---

Fixes tag targets the phy-index commit, as it introduced a change in
behaviour for PLCA. From what I can tell, coalesce never correctly
detected irq_moder in DUMP requests.

We could also consider fixing all individual commands that use
req_info->dev, however I'm not actually sure it's incorrect to do so,
feel free to correct me though.

Maxime

 net/ethtool/netlink.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index b4c45207fa32..de967961d8fe 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -582,6 +582,7 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
 		dev_hold(dev);
 		rcu_read_unlock();

+		ctx->req_info->dev = dev;
 		ret = ethnl_default_dump_one(skb, dev, ctx, genl_info_dump(cb));

 		rcu_read_lock();
-- 
2.48.1