netdev - Re: [patch net-next v3 03/10] flow_offload: check for basic action hw stats type

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Date:   Mon, 9 Mar 2020 12:17:22 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, saeedm@...lanox.com,
        leon@...nel.org, michael.chan@...adcom.com, vishal@...lsio.com,
        jeffrey.t.kirsher@...el.com, idosch@...lanox.com,
        aelior@...vell.com, peppe.cavallaro@...com,
        alexandre.torgue@...com, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        ecree@...arflare.com, mlxsw@...lanox.com
Subject: Re: [patch net-next v3 03/10] flow_offload: check for basic action
 hw stats type

On Sat, 7 Mar 2020 07:59:48 +0100 Jiri Pirko wrote:
> >> +static inline bool
> >> +flow_action_hw_stats_types_check(const struct flow_action *action,
> >> +				 struct netlink_ext_ack *extack,
> >> +				 u8 allowed_hw_stats_type)
> >> +{
> >> +	const struct flow_action_entry *action_entry;
> >> +
> >> +	if (!flow_action_has_entries(action))
> >> +		return true;
> >> +	if (!flow_action_mixed_hw_stats_types_check(action, extack))
> >> +		return false;
> >> +	action_entry = flow_action_first_entry_get(action);
> >> +	if (!allowed_hw_stats_type &&
> >> +	    action_entry->hw_stats_type != FLOW_ACTION_HW_STATS_TYPE_ANY) {
> >> +		NL_SET_ERR_MSG_MOD(extack, "Driver supports only default HW stats type \"any\"");
> >> +		return false;
> >> +	} else if (allowed_hw_stats_type &&
> >> +		   action_entry->hw_stats_type != allowed_hw_stats_type) {  
> >
> >Should this be an logical 'and' if we're doing it the bitfield way?  
> 
> No. I driver passes allowed_hw_stats_type != 0, means that allowed_hw_stats_type
> should be checked against action_entry->hw_stats_type.

Right, the "allowed_hw_stats_type &&" is fine.

> With bitfield, this is a bit awkward, I didn't figure out to do it
> better though.

The bitfield passed from user space means any of the set bits, right?

Condition would be better as:

allowed_hw_stats_type && (allowed_hw_stats_type & entry->hw_stats_type)

Otherwise passing more than one bit will not work well, no?

Driver can pass IMMEDIATE | DELAYED, action has IMMEDIATE, your
condition would reject it.. Same if driver has only one type and user
space asks for any of a few.

Drivers can't do a straight comparisons either, but:

if (act->stats & TYPE1) {
   /* preferred stats type*/
} else if (act->stats & TYPE2) {
   /* also supported, lower prio */
} else if (act->Stats & TYPE3) {
   /* lowest prio */
}