netdev - Re: [PATCH net-next v2 1/3] net: bridge: add support for user-controlled bool options

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Date:   Sat, 24 Nov 2018 18:46:27 +0200
From:   nikolay@...ulusnetworks.com
To:     Andrew Lunn <andrew@...n.ch>
CC:     netdev@...r.kernel.org, roopa@...ulusnetworks.com,
        davem@...emloft.net, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v2 1/3] net: bridge: add support for user-controlled bool options

On 24 November 2018 18:25:41 EET, Andrew Lunn <andrew@...n.ch> wrote:
>On Sat, Nov 24, 2018 at 06:18:33PM +0200, nikolay@...ulusnetworks.com
>wrote:
>> On 24 November 2018 18:10:41 EET, Andrew Lunn <andrew@...n.ch> wrote:
>> >> +int br_boolopt_toggle(struct net_bridge *br, enum br_boolopt_id
>opt,
>> >bool on,
>> >> +		      struct netlink_ext_ack *extack)
>> >> +{
>> >> +	switch (opt) {
>> >> +	default:
>> >> +		/* shouldn't be called with unsupported options */
>> >> +		WARN_ON(1);
>> >> +		break;
>> >
>> >So you return 0 here, meaning the br_debug() lower down will not
>> >happen. Maybe return -EOPNOTSUPP?
>> >
>> 
>> No, the idea here is that some option in the future might return an
>error. 
>> This function cannot be called with unsupported option thus the warn.
>
>
>O.K, i was trying to make it easier to see which option caused it to
>happen.
>
>> >> +	}
>> >> +
>> >> +	return 0;
>> >> +}
>> >> +
>> >
>> >> +int br_boolopt_multi_toggle(struct net_bridge *br,
>> >> +			    struct br_boolopt_multi *bm,
>> >> +			    struct netlink_ext_ack *extack)
>> >> +{
>> >> +	unsigned long bitmap = bm->optmask;
>> >> +	int err = 0;
>> >> +	int opt_id;
>> >> +
>> >> +	for_each_set_bit(opt_id, &bitmap, BR_BOOLOPT_MAX) {
>> >> +		bool on = !!(bm->optval & BIT(opt_id));
>> >> +
>> >> +		err = br_boolopt_toggle(br, opt_id, on, extack);
>> >> +		if (err) {
>> >> +			br_debug(br, "boolopt multi-toggle error: option: %d current:
>%d
>> >new: %d error: %d\n",
>> >> +				 opt_id, br_boolopt_get(br, opt_id), on, err);
>> >> +			break;
>> >> +		}
>> >> +	}
>> >
>> >Does the semantics of extack allow you to return something even when
>> >there is no error? If there are bits > BR_BOOLOPT_MAX you could
>return
>> >0, but also add a warning in extack that some bits where not
>supported
>> >by this kernel.
>> 
>> If we return 0 there's no reason to check extack. 
>
>Well, the caller can check to see if extack is present, even on
>success. This is extack, not extnack after all...
>

Evenif it's possible to return it without an error (I need to confirm that), the real problem is extack doesn't support
format strings, i. e. we can't say which bit is missing which makes it useless in this case IMO. 

>	 Andrew