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Date:   Sat, 17 Apr 2021 11:13:51 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Ido Schimmel <idosch@idosch.org>
Cc:     netdev@vger.kernel.org, davem@davemloft.net, andrew@lunn.ch,
        mkubecek@suse.cz, idosch@nvidia.com, saeedm@nvidia.com,
        michael.chan@broadcom.com
Subject: Re: [PATCH net-next v2 3/9] ethtool: add a new command for reading
 standard stats
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On Sat, 17 Apr 2021 10:57:42 -0700 Jakub Kicinski wrote:
> > I tried to understand how you add new groups without user space
> > changes and I think this statement is not entirely accurate.
> > 
> > At minimum, user space needs to know the names of these groups, but
> > currently there is no way to query the information, so it's added to
> > ethtool's help message:
> > 
> > ethtool [ FLAGS ] -S|--statistics DEVNAME       Show adapter statistics       
> >        [ --groups [eth-phy] [eth-mac] [eth-ctrl] [rmon] ]  
> 
> Um, yes and now. The only places the user space puts those names 
> is the help message and man page.
> 
> Thru the magic of bitsets it doesn't actually interpret them, so
> with old user space you can still query a new group, it will just 
> not show up in "ethtool -h".
> 
> Is that what you're saying?

FWIW ethnl_parse_bit() -> ETHTOOL_A_BITSET_BIT_NAME
User space can also use raw flags like --groups 0xf but that's perhaps
too spartan for serious use.