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

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Thu, Sep 13, 2018 at 02:05:54PM +0200, Michal Kubecek wrote:
> On Thu, Sep 13, 2018 at 01:25:15PM +0200, Johannes Berg wrote:
> > On Thu, 2018-09-13 at 12:49 +0200, Michal Kubecek wrote:
> > 
> > > >  		if (type > 0 && type <= maxtype) {
> > > >  			if (policy) {
> > > > -				err = validate_nla(nla, maxtype, policy);
> > > > +				err = validate_nla(nla, maxtype, policy,
> > > > +						   extack);
> > > >  				if (err < 0) {
> > > > -					NL_SET_ERR_MSG_ATTR(extack, nla,
> > > > -							    "Attribute failed policy validation");
> > > > +					NL_SET_BAD_ATTR(extack, nla);
> > > > +					if (extack && !extack->_msg)
> > > > +						NL_SET_ERR_MSG(extack,
> > > > +							       "Attribute failed policy validation");
> > > >  					goto errout;
> > > >  				}
> > > >  			}
> > > > -- 
> > > 
> > > Technically, this would change the outcome when nla_parse() is called
> > > with extack->_msg already set nad validate_nla() fails on something else
> > > than NLA_REJECT; it will preserve the previous message in such case.
> > > But I don't think this is a serious problem.
> > 
> > Yes, that's true. I looked at quite a few of the setters just now (there
> > are ~500 already, wow!), and they all set & return, so this shouldn't be
> > an issue.
> 
> In ethtool (work in progress) I sometimes use extack message for
> non-fatal warnings but AFAICS never before parsing the userspace
> request (actually always shortly before returning). So I don't have
> a problem with it.

Considering we can only report 1 message, it should be okay to drop
the previous message in favor of the new one, which is either a
critical one or just another non-fatal one.

  Marcelo