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

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Message-ID: <2f1a8edb0b000b4eb7adcaca0d1fb05fdd73a587.camel@sipsolutions.net>
Date:   Thu, 04 Jul 2019 14:21:52 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Michal Kubecek <mkubecek@...e.cz>, netdev@...r.kernel.org
Cc:     Jiri Pirko <jiri@...nulli.us>, David Miller <davem@...emloft.net>,
        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 Thu, 2019-07-04 at 14:17 +0200, Michal Kubecek wrote:
> On Thu, Jul 04, 2019 at 02:03:02PM +0200, Johannes Berg wrote:
> > On Thu, 2019-07-04 at 13:52 +0200, Michal Kubecek wrote:
> > > 
> > > There is still the question if it it should be implemented as a nested
> > > attribute which could look like the current compact form without the
> > > "list" flag (if there is no mask, it's a list). Or an unstructured data
> > > block consisting of u32 bit length 
> > 
> > You wouldn't really need the length, since the attribute has a length
> > already :-)
> 
> It has byte length, not bit length. The bitmaps we are dealing with
> can have any bit length, not necessarily multiples of 8 (or even 32).

Not sure why that matters? You have the mask, so you don't really need
to additionally say that you're only going up to a certain bit?

I mean, say you want to set some bits <=17, why would you need to say
that they're <=17 if you have a
 value: 0b00000000'000000xx'xxxxxxxx'xxxxxxxx
 mask:  0b00000000'00000011'11111111'11111111

johannes