netdev - Re: [PATCH net-next v6 06/15] ethtool: netlink bitset handling

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Date:   Thu, 04 Jul 2019 14:07:16 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Michal Kubecek <mkubecek@...e.cz>,
        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 v6 06/15] ethtool: netlink bitset handling

On Wed, 2019-07-03 at 16:37 +0200, Jiri Pirko wrote:
> Wed, Jul 03, 2019 at 03:44:57PM CEST, johannes@...solutions.net wrote:
> > On Wed, 2019-07-03 at 13:49 +0200, Jiri Pirko wrote:
> > > 
> > > > +Value and mask must have length at least ETHTOOL_A_BITSET_SIZE bits rounded up
> > > > +to a multiple of 32 bits. They consist of 32-bit words in host byte order,
> > > 
> > > Looks like the blocks are similar to NLA_BITFIELD32. Why don't you user
> > > nested array of NLA_BITFIELD32 instead?
> > 
> > That would seem kind of awkward to use, IMHO.
> > 
> > Perhaps better to make some kind of generic "arbitrary size bitfield"
> > attribute type?
> 
> Yep, I believe I was trying to make this point during bitfield32
> discussion, failed apparently. So if we have "NLA_BITFIELD" with
> arbitrary size, that sounds good to me.

I guess it could be the same way - just have the content be

u32 value[N];
u32 select[N];

where N = nla_len(attr) / 8

That'd be compatible with NLA_BITFIELD32, and we could basically change
all occurrences of NLA_BITFIELD32 to NLA_BITFIELD, and have NLA_BITFIELD
take something like a "max_bit" for the .len field or something like
that? And an entry in the validation union to point to a "u32 *mask"
instead of the current validation_data that just points to a single u32
mask...

So overall seems like a pretty simple extension to NLA_BITFIELD32 that
handles NLA_BITFIELD32 as a special case with simply .len=32.

(len is a 16-bit field, but a 64k bitmap should be sufficient I hope?)

johannes