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

From: Jiri Pirko <[email-masked]>
Date: Wed, 27 Mar 2019 10:57:49 +0100

Tue, Mar 26, 2019 at 06:59:32PM CET, [email-masked] wrote:
>On Tue, Mar 26, 2019 at 04:59:11PM +0100, Jiri Pirko wrote:
>> Mon, Mar 25, 2019 at 06:08:15PM CET, [email-masked] 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?

>
>> 2) Did you think about leveraging NLA_BITFIELD32? What I mean is this:
>> NEST_START
>>    NLA_BITFIELD32 index 0 (bit 0-31)
>>    NLA_BITFIELD32 index 1 (bit 32-63)
>>    NLA_BITFIELD32 index 2 (bit 64-95)
>>    NLA_BITFIELD32 index 3 (bit 96-127)
>>    ....
>> NEST_END
>> It is basically an array of NLA_BITFIELD32.
>
>That would be similar to compact form but it would introduce the
>interleaving and extra struct nlattr header for each block. I don't
>think it would make things easier.

I'm just trying to figure out if it would be possible to use existing
building block instead of introducing new ones....

>
>The verbose form is meant to allow requests like
>
>  ethtool -K eth0 tx-vlan-stag-hw-insert on
>  ethtool -s eth0 advertise 1000baseT/Full off
>
>without either keeping the table of available flags in sync between
>kernel and userspace (all userspace users of the API) or having to ask
>for the list first (in case of one shot requests as above; long running
>tools like "ethtool --monitor" or config management daemons would keep
>the tables and use compact form).

Okay, I have to go over those patches but this smells.

>Michal