netdev - Re: [PATCH net-next v5 07/22] ethtool: netlink bitset handling

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Message-ID: <20190327101923.GR26076@unicorn.suse.cz>
Date:   Wed, 27 Mar 2019 11:19:23 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 07/22] ethtool: netlink bitset handling

On Wed, Mar 27, 2019 at 10:57:49AM +0100, Jiri Pirko wrote:
> Tue, Mar 26, 2019 at 06:59:32PM CET, mkubecek@...e.cz wrote:
> >On Tue, Mar 26, 2019 at 04:59:11PM +0100, Jiri Pirko wrote:
> >> Mon, Mar 25, 2019 at 06:08:15PM CET, mkubecek@...e.cz wrote:
> >> >Declare attribute type constants and add helper functions to generate and
> >> >parse arbitrary length bit sets.
> >> 
> >> Hmm, this looks like a lot of work. Two things:
> >> 1) This is generic. Not really related to ethtool in any way. Could this
> >>    be done in netlink common code?
> >
> >I suppose it could if other netlink based APIs would be interested in
> >using it. The only ethtool specific part is the support for "legacy
> >style names" (fixed size strings) but that is something I'm not really
> >happy about.  Perhaps it's time to return to the original idea of
> >supporting only arrays of (char *) and creating them around existing
> >fixed size ones.
> 
> Wait, could you please describe this more?

At the moment, there are two formats of bit name tables. Legacy format
which is used by ioctl string sets, e.g.

const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN] = {
	...
};

(the same is provided by NIC drivers with ethtool_ops::get_strings())
and simple format used for newly added string sets, e.g.

const char *const link_mode_names[] = {
	...
};

If the bitset implementation is to be used by other APIs, legacy format
support would make little sense so I would suggest to drop legacy format
support from bitset code and build a (const char **) "index" for ethtool
legacy string arrays before passing it to bitset related functions.

Michal