netdev - [PATCH net 1/2] net: ethtool: fix ethtool_ringparam_get_cfg() returns a hds

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Message-Id: <20250403060423.1209435-2-ap420073@gmail.com>
Date: Thu,  3 Apr 2025 06:04:22 +0000
From: Taehee Yoo <ap420073@...il.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
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Cc: kory.maincent@...tlin.com,
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	ap420073@...il.com
Subject: [PATCH net 1/2] net: ethtool: fix ethtool_ringparam_get_cfg() returns a hds_thresh value always as 0.

When hds-thresh is configured, ethnl_set_rings() is called, and it calls
ethtool_ringparam_get_cfg() to get ringparameters from .get_ringparam()
callback and dev->cfg.
Both hds_config and hds_thresh values should be set from dev->cfg, not
from .get_ringparam().
But ethtool_ringparam_get_cfg() sets only hds_config from dev->cfg.
So, ethtool_ringparam_get_cfg() returns always a hds_thresh as 0.

If an input value of hds-thresh is 0, a hds_thresh value from
ethtool_ringparam_get_cfg() are same. So ethnl_set_rings() does
nothing and returns immediately.
It causes a bug that setting a hds-thresh value to 0 is not working.

Reproducer:
    modprobe netdevsim
    echo 1 > /sys/bus/netdevsim/new_device
    ethtool -G eth0 hds-thresh 100
    ethtool -G eth0 hds-thresh 0
    ethtool -g eth0
    #hds-thresh value should be 0, but it shows 100.

The tools/testing/selftests/drivers/net/hds.py can test it too with
applying a following patch for hds.py.

Fixes: 928459bbda19 ("net: ethtool: populate the default HDS params in the core")
Signed-off-by: Taehee Yoo <ap420073@...il.com>
---

The ethtool command doesn't support hds-thresh option yet.
So, RFC[1] patch is needed to be applied.

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

diff --git a/net/ethtool/common.c b/net/ethtool/common.c
index 0cb6da1f692a..49bea6b45bd5 100644
--- a/net/ethtool/common.c
+++ b/net/ethtool/common.c
@@ -830,6 +830,7 @@ void ethtool_ringparam_get_cfg(struct net_device *dev,

 	/* Driver gives us current state, we want to return current config */
 	kparam->tcp_data_split = dev->cfg->hds_config;
+	kparam->hds_thresh = dev->cfg->hds_thresh;
 }

 static void ethtool_init_tsinfo(struct kernel_ethtool_ts_info *info)
-- 
2.34.1