Re: [PATCH net-next v3 2/5] net: core: factor out the GSO device limit check

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Wang Zhan wrote:
> gso_features_check() decides whether an egress device can offload a GSO
> skb as a single TSO frame by comparing the segment count and the frame
> length against the device limits.  The resegmentation path added by a
> later patch caps the MSS segments per output skb and needs the same
> features computed without those limits, so put the two tests in a helper
> and gate them with one flag.
> 
> No functional changes.
> 
> Assisted-by: LLM
> Signed-off-by: Wang Zhan <wang.zhan@smartx.com>
> 
> ---
> v3:
> - rename the helper to gso_within_dev_limits
> - move the check_gso_limits flag and the wrapper split here from patch 4
> v2: https://lore.kernel.org/20260918084651.3022878-2-wang.zhan@smartx.com/
> v1: https://lore.kernel.org/20260917063854.2011613-2-wang.zhan@smartx.com/
> ---
>  net/core/dev.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index ffa9b0c27788c..d66b667071837 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3834,17 +3834,19 @@ static bool skb_gso_has_extension_hdr(const struct sk_buff *skb)
>  			 skb_inner_network_header_len(skb) != sizeof(struct ipv6hdr)));
>  }
>  
> +static bool
> +gso_within_dev_limits(const struct sk_buff *skb, const struct net_device *dev)
> +{
> +	return skb_shinfo(skb)->gso_segs <= READ_ONCE(dev->gso_max_segs) &&
> +	       skb->len < netif_get_gso_max_size(dev, vlan_get_protocol(skb));

nit: keep the separate return statements as before. It's easier to read.
> +}
> +
>  static netdev_features_t gso_features_check(const struct sk_buff *skb,
>  					    struct net_device *dev,
> -					    netdev_features_t features)
> +					    netdev_features_t features,
> +					    bool check_limits)
>  {
> -	u16 gso_segs = skb_shinfo(skb)->gso_segs;
> -
> -	if (gso_segs > READ_ONCE(dev->gso_max_segs))
> -		return features & ~NETIF_F_GSO_MASK;
> -
> -	if (unlikely(skb->len >=
> -		     netif_get_gso_max_size(dev, vlan_get_protocol(skb))))
> +	if (check_limits && !gso_within_dev_limits(skb, dev))
>  		return features & ~NETIF_F_GSO_MASK;
>  
>  	if (!skb_shinfo(skb)->gso_type) {
> @@ -3893,13 +3895,15 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
>  	return features;
>  }
>  
> -netdev_features_t netif_skb_features(struct sk_buff *skb)
> +static netdev_features_t
> +__netif_skb_features(struct sk_buff *skb, bool check_gso_limits)
>  {
>  	struct net_device *dev = skb->dev;
>  	netdev_features_t features = dev->features;
>  
>  	if (skb_is_gso(skb))
> -		features = gso_features_check(skb, dev, features);
> +		features = gso_features_check(skb, dev, features,
> +					      check_gso_limits);
>  
>  	/* If encapsulation offload request, verify we are testing
>  	 * hardware encapsulation features instead of standard
> @@ -3922,6 +3926,11 @@ netdev_features_t netif_skb_features(struct sk_buff *skb)
>  
>  	return harmonize_features(skb, features);
>  }
> +
> +netdev_features_t netif_skb_features(struct sk_buff *skb)
> +{
> +	return __netif_skb_features(skb, true);
> +}
>  EXPORT_SYMBOL(netif_skb_features);
>  
>  static int xmit_one(struct sk_buff *skb, struct net_device *dev,
> -- 
> 2.47.3
>