netdev - Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL device

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Date: Fri, 16 Feb 2024 10:41:52 -0800
From: Florian Fainelli <f.fainelli@...il.com>
To: Stephen Hemminger <stephen@...workplumber.org>,
 Breno Leitao <leitao@...ian.org>
Cc: kuba@...nel.org, davem@...emloft.net, pabeni@...hat.com,
 edumazet@...gle.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 horms@...nel.org, Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL
 device

On 2/16/24 09:29, Stephen Hemminger wrote:
> On Fri, 16 Feb 2024 01:41:52 -0800
> Breno Leitao <leitao@...ian.org> wrote:
> 
>> +static bool netdev_uses_bql(const struct net_device *dev)
>> +{
>> +	if (dev->features & NETIF_F_LLTX ||
>> +	    dev->priv_flags & IFF_NO_QUEUE)
>> +		return false;
>> +
>> +	return IS_ENABLED(CONFIG_BQL);
>> +}
> 
> Various compilers will warn about missing parens in that expression.
> It is valid but mixing & and || can be bug trap.
> 
> 	if ((dev->features & NETIF_F_LLTX) || (dev->priv_flags & IFF_NO_QUEUE))
> 		return false;
> 
> Not all drivers will be using bql, it requires driver to have that code.
> So really it means driver could be using BQL.
> Not sure if there is a way to find out if driver has the required BQL bits.

There is not a feature flag to be keying off if that is what you are 
after, you would need to audit the drivers and see whether they make 
calls to netdev_tx_sent_queue(), netdev_tx_reset_queue(), 
netdev_tx_completed_queue().

I suppose you might be able to programmatically extract that information 
by looking at whether a given driver object file has a reference to 
dql_{reset,avail,completed} or do that at the source level, whichever is 
easier.
-- 
Florian