netdev - Re: [PATCH iproute2] devlink: Ignore unknown attributes

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Date:   Fri, 19 Jan 2018 14:02:31 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     David Ahern <dsahern@...il.com>
Cc:     Arkadi Sharshevsky <arkadis@...lanox.com>, netdev@...r.kernel.org,
        davem@...emloft.net, mlxsw@...lanox.com
Subject: Re: [PATCH iproute2] devlink: Ignore unknown attributes

On Thu, 18 Jan 2018 20:42:44 -0800
David Ahern <dsahern@...il.com> wrote:

> On 1/17/18 5:28 AM, Arkadi Sharshevsky wrote:
> > In case of extending the UAPI old packages would break.
> > 
> > Signed-off-by: Arkadi Sharshevsky <arkadis@...lanox.com>
> > ---
> >  devlink/devlink.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/devlink/devlink.c b/devlink/devlink.c
> > index 39cda06..c9d1838 100644
> > --- a/devlink/devlink.c
> > +++ b/devlink/devlink.c
> > @@ -343,7 +343,7 @@ static int attr_cb(const struct nlattr *attr, void *data)
> >  	int type;
> >  
> >  	if (mnl_attr_type_valid(attr, DEVLINK_ATTR_MAX) < 0)
> > -		return MNL_CB_ERROR;
> > +		return MNL_CB_OK;
> >  
> >  	type = mnl_attr_get_type(attr);
> >  	if (mnl_attr_validate(attr, devlink_policy[type]) < 0)
> >   
> 
> What's the point of calling mnl_attr_type_valid if you disregard a
> failure? you might as well not call mnl_attr_type_valid at all.

The way mnl handles attributes, you have to have a callback and it is up
to the callback to copy the values it wants.  The idea is that old code
running against a newer kernel will have a smaller array of attributes
it wants, and only copy those.