netdev - Re: [PATCH v4 net-next 04/10] net/ncsi: Ethtool operation to get NCSI topology

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Date:   Thu, 4 May 2017 02:49:33 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Gavin Shan <gwshan@...ux.vnet.ibm.com>
Cc:     netdev@...r.kernel.org, joe@...ches.com, kubakici@...pl,
        f.fainelli@...il.com, davem@...emloft.net
Subject: Re: [PATCH v4 net-next 04/10] net/ncsi: Ethtool operation to get
 NCSI topology

> +void ncsi_ethtool_register_dev(struct net_device *dev)
> +{
> +	struct ethtool_ops *ops;
> +
> +	ops = (struct ethtool_ops *)(dev->ethtool_ops);

Why do you need the cast here?

Ah, is it because net_device has:

          const struct ethtool_ops *ethtool_ops;

i.e. you are casting off the const.

> +	if (!ops)
> +		return;
> +
> +	ops->get_ncsi_channels = ncsi_get_channels;

and here you modify it. Which is going to blow up, because it will be
in a read only segment and should throw an opps when you write to it?

You need to export ncsi_get_channels, and let the underlying driver
add it to its own ethtool_ops.

   Andrew