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Date: Thu, 23 Jan 2020 09:28:21 +0100 From: Michal Kubecek <mkubecek@...e.cz> To: netdev@...r.kernel.org Cc: Luigi Rizzo <lrizzo@...gle.com>, Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net> Subject: Re: [PATCH] net-core: remove unnecessary ETHTOOL_GCHANNELS initialization On Wed, Jan 22, 2020 at 04:18:56PM -0800, Luigi Rizzo wrote: > On Wed, Jan 22, 2020 at 3:47 PM Andrew Lunn <andrew@...n.ch> wrote: > > > > On Wed, Jan 22, 2020 at 02:33:26PM -0800, Luigi Rizzo wrote: > > > struct ethtool_channels does not need .cmd to be set when calling the > > > driver's ethtool methods. Just zero-initialize it. > > > > > > Tested: run ethtool -l and ethtool -L > > > > Hi Luigi > > > > This seems pretty risky. You are assuming ethtool is the only user of > > this API. What is actually wrong with putting a sane cmd value, rather > > than the undefined value 0. > > Hi Andrew, if I understand correctly your suggestion is that even if > the values are unused, it is better to stay compliant with the header > file include/uapi/linux/ethtool.h, which does suggest a value for .cmd > for the various structs The point is that unless you check ethtool_ops::get_channels() of all in tree drivers, you cannot be sure there isn't one which depends on .cmd being set to expected value. And even then there could be some out of tree drivers; we usually don't care too much about those but it's always question of what you gain by the cleanup. AFAICS, in this case it might be few CPU cycles and even that isn't really sure. > and only replace the value in ethtool_set_channels() with the correct > one ETHTOOL_SCHANNELS ? That would be incorrect. In ethtool_set_channels(), the structure initialized is curr which is used with ->get_channels() to get current values (for comparison of new values against driver maximum) so that ETHTOOL_GCHANNELS is the right command. Michal
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