linux-kernel - Re: [RFC PATCH net-next v3 13/21] ethtool: provide timestamping information in GET

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Date:   Wed, 20 Feb 2019 10:37:09 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>, Jiri Pirko <jiri@...nulli.us>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next v3 13/21] ethtool: provide timestamping
 information in GET_INFO request

On Wed, 20 Feb 2019 14:00:07 +0100, Michal Kubecek wrote:
> On Tue, Feb 19, 2019 at 07:00:48PM -0800, Jakub Kicinski wrote:
> > On Mon, 18 Feb 2019 19:22:29 +0100 (CET), Michal Kubecek wrote:  
> > > Add timestamping information as provided by ETHTOOL_GET_TS_INFO ioctl
> > > command in GET_INFO reply if ETH_INFO_IM_TSINFO flag is set in the request.
> > > 
> > > Add constants for counts of HWTSTAMP_TX_* and HWTSTAM_FILTER_* constants
> > > and provide symbolic names for timestamping related values so that they can
> > > be retrieved in GET_STRSET and GET_INFO requests.  
> > 
> > What's the reason for providing the symbolic names?  
> 
> One of the the goals I had was to reduce the need to keep the lists of
> possible values in sync between kernel and userspace ethtool and other
> users of the interface so that when a new value is added, we don't have
> to update all userspace tools to be able to use or present it.
> 
> This already works in ethtool for some newer commands (e.g. features)
> and obviously for those where the list of available options depends on
> the device (e.g. private flags or statistics). I would like to extend
> the principle also to older commands and new ones which do not work like
> this (e.g. device reset).

Let me try to argue that's the wrong direction.  People should learn to
update their user space tooling if they want access to new features.  
In my (limited) experience trying to solve forward compatibility leads
to short term gains, and long term warts in the APIs and increased
maintenance burden in the kernel.