netdev - Re: [PATCH v2 net-next] net/core: generic support for disabling netdev features down stack

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Date:	Sat, 2 Apr 2016 04:21:15 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Veaceslav Falico <vfalico@...il.com>,
	Andy Gospodarek <gospo@...ulusnetworks.com>,
	Jiri Pirko <jiri@...nulli.us>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Michal Kubecek <mkubecek@...e.cz>,
	Alexander Duyck <alexander.duyck@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] net/core: generic support for disabling
 netdev features down stack

Hi,

Sorry for digging up an old patch, but... ;-)

dev_disable_lro() is a leftover from ancient times. If you read commit
27660515a,
there is a hint where it should go. Please, read on if you'd like to
fix this properly.

2015-11-03 3:55 GMT+01:00 Jarod Wilson <jarod@...hat.com>:
> There are some netdev features, which when disabled on an upper device,
> such as a bonding master or a bridge, must be disabled and cannot be
> re-enabled on underlying devices.
[...]
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6288,6 +6288,44 @@ static void rollback_registered(struct net_device *dev)
>         list_del(&single);
>  }
>
> +static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
> +       struct net_device *upper, netdev_features_t features)
> +{
> +       netdev_features_t upper_disables = NETIF_F_UPPER_DISABLES;
> +       netdev_features_t feature;
> +
> +       for_each_netdev_feature(&upper_disables, feature) {
> +               if (!(upper->wanted_features & feature)
> +                   && (features & feature)) {
> +                       netdev_dbg(lower, "Dropping feature %pNF, upper dev %s has it off.\n",
> +                                  &feature, upper->name);
> +                       features &= ~feature;
> +               }
> +       }

You could do this once:

disable_features = ~upper->features & features & NETIF_F_UPPER_DISABLES;
if (features & disable_features)
  netdev_dbg(...)
features &= ~disable_features;

> +
> +       return features;
> +}
[...]
> @@ -6370,6 +6410,10 @@ int __netdev_update_features(struct net_device *dev)
>         /* driver might be less strict about feature dependencies */
>         features = netdev_fix_features(dev, features);
>
> +       /* some features can't be enabled if they're off an an upper device */
> +       netdev_for_each_upper_dev_rcu(dev, upper, iter)
> +               features = netdev_sync_upper_features(dev, upper, features);
> +
>         if (dev->features == features)
>                 return 0;
>

This should go into netdev_fix_features(), as it is a one single place,
where are feature dependencies are verified.

[...]
> @@ -6386,6 +6430,12 @@ int __netdev_update_features(struct net_device *dev)
>                 return -1;
>         }
>
> +       /* some features must be disabled on lower devices when disabled
> +        * on an upper device (think: bonding master or bridge)
> +        */
> +       netdev_for_each_lower_dev(dev, lower, iter)
> +               netdev_sync_lower_features(dev, lower, features);
> +
[...]

This should be equal in resulting flags to:

   netdev_for_each_lower_dev(dev, lower...)
     netdev_update_features(lower);

because netdev_fix_features(lower) will see already changed dev->features.

Best Regards,
Michał Mirosław