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

[Wang Zhan <wang.zhan@smartx.com>]

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));
+}
+
 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