netdev - Re: [PATCHv2 net-next 1/5] net: add a common function to compute features from lowers devices

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Message-ID: <aLxymFjpPjckFb2Q@krikkit>
Date: Sat, 6 Sep 2025 19:42:48 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org, Jay Vosburgh <jv@...sburgh.net>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jiri Pirko <jiri@...nulli.us>, Simon Horman <horms@...nel.org>,
	Ido Schimmel <idosch@...dia.com>, Shuah Khan <shuah@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Ahmed Zaki <ahmed.zaki@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	bridge@...ts.linux.dev, linux-kselftest@...r.kernel.org
Subject: Re: [PATCHv2 net-next 1/5] net: add a common function to compute
 features from lowers devices

2025-09-02, 07:25:58 +0000, Hangbin Liu wrote:
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 1d1650d9ecff..5c1c8b016c8e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -12577,6 +12577,82 @@ netdev_features_t netdev_increment_features(netdev_features_t all,
>  }
>  EXPORT_SYMBOL(netdev_increment_features);
>  
> +/**
> + *	netdev_compute_features_from_lowers - compute feature from lowers
> + *	@dev: the upper device
> + *
> + *	Recompute the upper device's feature based on all lower devices.
> + */
> +void netdev_compute_features_from_lowers(struct net_device *dev)
> +{
> +	unsigned int dst_release_flag = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
> +	netdev_features_t gso_partial_features = VIRTUAL_DEV_GSO_PARTIAL_FEATURES;
> +#ifdef CONFIG_XFRM_OFFLOAD
> +	netdev_features_t xfrm_features  = VIRTUAL_DEV_XFRM_FEATURES;
> +#endif
> +	netdev_features_t mpls_features  = VIRTUAL_DEV_MPLS_FEATURES;
> +	netdev_features_t vlan_features = VIRTUAL_DEV_VLAN_FEATURES;
> +	netdev_features_t enc_features  = VIRTUAL_DEV_ENC_FEATURES;
> +	unsigned int tso_max_size = TSO_MAX_SIZE;
> +	u16 tso_max_segs = TSO_MAX_SEGS;
> +	struct net_device *lower_dev;
> +	struct list_head *iter;
> +
> +	mpls_features = netdev_base_features(mpls_features);
> +	vlan_features = netdev_base_features(vlan_features);
> +	enc_features = netdev_base_features(enc_features);
> +
> +	netdev_for_each_lower_dev(dev, lower_dev, iter) {
> +		gso_partial_features = netdev_increment_features(gso_partial_features,
> +								 lower_dev->gso_partial_features,
> +								 VIRTUAL_DEV_GSO_PARTIAL_FEATURES);
> +
> +		vlan_features = netdev_increment_features(vlan_features,
> +							  lower_dev->vlan_features,
> +							  VIRTUAL_DEV_VLAN_FEATURES);
> +
> +#ifdef CONFIG_XFRM_OFFLOAD
> +		xfrm_features = netdev_increment_features(xfrm_features,
> +							  lower_dev->hw_enc_features,
> +							  VIRTUAL_DEV_XFRM_FEATURES);
> +#endif
> +
> +		enc_features = netdev_increment_features(enc_features,
> +							 lower_dev->hw_enc_features,
> +							 VIRTUAL_DEV_ENC_FEATURES);
> +
> +		mpls_features = netdev_increment_features(mpls_features,
> +							  lower_dev->mpls_features,
> +							  VIRTUAL_DEV_MPLS_FEATURES);
> +
> +		dst_release_flag &= lower_dev->priv_flags;
> +
> +		tso_max_size = min(tso_max_size, lower_dev->tso_max_size);
> +		tso_max_segs = min(tso_max_segs, lower_dev->tso_max_segs);
> +	}
> +
> +	dev->gso_partial_features = gso_partial_features;
> +	dev->vlan_features = vlan_features;
> +#ifdef CONFIG_XFRM_OFFLOAD
> +	dev->hw_enc_features |= xfrm_features;
> +#endif

I'm not completely sure we want xfrm_features for upper devices other
than bonding [1], but this will get overwritten immediately
afterwards:

> +	dev->hw_enc_features = enc_features | NETIF_F_GSO_ENCAP_ALL |
> +				    NETIF_F_HW_VLAN_CTAG_TX |
> +				    NETIF_F_HW_VLAN_STAG_TX;


[1] those lines in bond_compute_features were only added alongside
bond IPsec offload, see 18cb261afd7b ("bonding: support hardware
encryption offload to slaves")

but AFAIU hw_enc_features is only used as a mask over dev->features so
it shouldn't be a problem to have xfrm stuff in bridge/team as well

-- 
Sabrina