[net,1/2] net: ethtool: fix ethtool_ringparam_get_cfg() returns a hds_thresh value always as 0.

Commit Message

Taehee Yoo April 3, 2025, 6:04 a.m. UTC

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 <[e-mail]>
---

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(+)

Patch

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)