netdev - Re: [PATCH net-next v11 1/4] net netlink: Add new type NLA_BITFIELD

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Date:   Fri, 28 Jul 2017 16:08:40 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     David Ahern <dsahern@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, xiyou.wangcong@...il.com,
        eric.dumazet@...il.com, mrv@...atatu.com,
        simon.horman@...ronome.com, alex.aring@...il.com
Subject: Re: [PATCH net-next v11 1/4] net netlink: Add new type
 NLA_BITFIELD_32

Fri, Jul 28, 2017 at 03:51:41PM CEST, jhs@...atatu.com wrote:
>On 17-07-25 10:41 AM, David Ahern wrote:
>> On 7/23/17 7:35 PM, Jamal Hadi Salim wrote:
>> > In the most basic form, the user specifies the attribute policy as:
>> > [ATTR_GOO] = { .type = NLA_BITFIELD_32, .validation_data = &myvalidflags },
>> > 
>> > where myvalidflags is the bit mask of the flags the kernel understands.
>> > 
>> > If the user _does not_ provide myvalidflags then the attribute will
>> > also be rejected.
>> 
>> No other netlink attribute has this requirement.
>
>This is the first one where we have to inspect content. We add things
>when we need them - as in this case.
>
>> Users of the attributes
>> are the only ones that know if a value is valid or not (e.g, attribute
>> passing a device index) and those are always checked in line.
>
>It doesnt make sense that every user of the API has to repeat that
>validation code. Same principle as someone specifying that a type is
>u32 and have the nla validation check it. At some point we never had
>the u32 validation code. Then it was factored out because everyone
>repeats the same boilerplate code.
>I see this in the same spirit.

Agreed.