From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Lunn <andrew@lunn.ch>
Subject: Re: [PATCH v4 net-next 04/10] net/ncsi: Ethtool operation to get
 NCSI topology
Date: Thu, 4 May 2017 02:49:33 +0200
Message-ID: <20170504004933.GP8029@lunn.ch>
References: <1493786681-27468-1-git-send-email-gwshan@linux.vnet.ibm.com>
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To: Gavin Shan <gwshan@linux.vnet.ibm.com>
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> +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