netdev - Re: [PATCH net-next 05/13] genetlink: check for callback type at op load time

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Message-ID: <20221019144534.04d22ced@kernel.org>
Date:   Wed, 19 Oct 2022 14:45:34 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     <davem@...emloft.net>, <johannes@...solutions.net>,
        <netdev@...r.kernel.org>, <edumazet@...gle.com>,
        <pabeni@...hat.com>, <jiri@...nulli.us>, <razor@...ckwall.org>,
        <nicolas.dichtel@...nd.com>, <gnault@...hat.com>, <fw@...len.de>
Subject: Re: [PATCH net-next 05/13] genetlink: check for callback type at op
 load time

On Wed, 19 Oct 2022 14:33:39 -0700 Jacob Keller wrote:
> > +static int
> >  genl_cmd_full_to_split(struct genl_split_ops *op,
> >  		       const struct genl_family *family,
> >  		       const struct genl_ops *full, u8 flags)
> >  {
> > +	if ((flags & GENL_CMD_CAP_DO && !full->doit) ||
> > +	    (flags & GENL_CMD_CAP_DUMP && !full->dumpit)) {
> > +		memset(op, 0, sizeof(*op));
> > +		return -ENOENT;
> > +	}
> > +  
> 
> Should this check that exactly one of GENL_CMD_CAP_DO and
> GENL_CMD_CAP_DUMP is set? Or is some earlier flow enforcing this?

I check at registration time that the family-provided flags only 
have one of those two set. Internally, inside genetlink.c it'd be 
a programming error to request both at the same time, IOW it'd be
defensive programming to check for it.