Re: [PATCH v2 1/2] netlink: add NLA_REJECT policy type

[David Miller <davem@redhat.com>]

From: Johannes Berg <johannes@sipsolutions.net>
Date: Mon, 17 Sep 2018 11:57:28 +0200

> From: Johannes Berg <johannes.berg@intel.com>
> 
> In some situations some netlink attributes may be used for output
> only (kernel->userspace) or may be reserved for future use. It's
> then helpful to be able to prevent userspace from using them in
> messages sent to the kernel, since they'd otherwise be ignored and
> any future will become impossible if this happens.
> 
> Add NLA_REJECT to the policy which does nothing but reject (with
> EINVAL) validation of any messages containing this attribute.
> Allow for returning a specific extended ACK error message in the
> validation_data pointer.
> 
> While at it clear up the documentation a bit - the NLA_BITFIELD32
> documentation was added to the list of len field descriptions.
> 
> Also, use NL_SET_BAD_ATTR() in one place where it's open-coded.
> 
> The specific case I have in mind now is a shared nested attribute
> containing request/response data, and it would be pointless and
> potentially confusing to have userspace include response data in
> the messages that actually contain a request.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
> v2: preserve behaviour of overwriting the extack message, with
>     either the generic or the specific one now

Applied.