netdev - Re: [PATCH 1/2] netlink: add NLA

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Date:   Thu, 13 Sep 2018 14:05:54 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] netlink: add NLA_REJECT policy type

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.

Michal Kubecek