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

Commit Message

Maxime Chevallier March 2, 2025, 4:21 p.m. UTC

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 <[e-mail]>
---

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(+)

Patch

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();