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

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Date:   Tue, 25 Jul 2017 08:41:43 -0600
From:   David Ahern <dsahern@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, 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

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. 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.
Furthermore, you are locking this attribute into a static meaning of
what is a valid value when flags can be valid or invalid based on other
attributes passed in the request.