[PATCH net-next v4 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.

__netif_skb_features() takes that flag and takes the place of
netif_skb_features(), which becomes an inline wrapper in netdevice.h and
passes the flag set.  Existing callers keep their call, and the
resegmentation path asks for the features without the limit checks.

No functional changes.

Assisted-by: LLM
Signed-off-by: Wang Zhan <wang.zhan@smartx.com>

---
v4:
- keep the two limit tests as separate returns
- move the wrapper into netdevice.h, export __netif_skb_features()
v3: https://lore.kernel.org/20260928044102.1004310-3-wang.zhan@smartx.com/
v2: https://lore.kernel.org/20260918084651.3022878-2-wang.zhan@smartx.com/
v1: https://lore.kernel.org/20260917063854.2011613-2-wang.zhan@smartx.com/
---
 include/linux/netdevice.h |  9 ++++++++-
 net/core/dev.c            | 30 ++++++++++++++++++++----------
 2 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 421c0f5952463e..5b7b0c87e4f637 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -5495,7 +5495,14 @@ void netif_stacked_transfer_operstate(const struct net_device *rootdev,
 netdev_features_t passthru_features_check(struct sk_buff *skb,
 					  struct net_device *dev,
 					  netdev_features_t features);
-netdev_features_t netif_skb_features(struct sk_buff *skb);
+netdev_features_t __netif_skb_features(struct sk_buff *skb,
+				       bool check_gso_limits);
+
+static inline netdev_features_t netif_skb_features(struct sk_buff *skb)
+{
+	return __netif_skb_features(skb, true);
+}
+
 void skb_warn_bad_offload(const struct sk_buff *skb);
 
 static inline bool net_gso_ok(netdev_features_t features, int gso_type)
diff --git a/net/core/dev.c b/net/core/dev.c
index 8475d5da64fdf0..a6213c9ed5e721 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3878,16 +3878,24 @@ netif_get_gso_max_size(const struct net_device *dev, const struct sk_buff *skb)
 	       READ_ONCE(dev->gso_ipv4_max_size);
 }
 
+static bool
+gso_within_dev_limits(const struct sk_buff *skb, const struct net_device *dev)
+{
+	if (skb_shinfo(skb)->gso_segs > READ_ONCE(dev->gso_max_segs))
+		return false;
+
+	if (unlikely(skb->len >= netif_get_gso_max_size(dev, skb)))
+		return false;
+
+	return true;
+}
+
 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, skb)))
+	if (check_limits && !gso_within_dev_limits(skb, dev))
 		return features & ~NETIF_F_GSO_MASK;
 
 	if (!skb_shinfo(skb)->gso_type) {
@@ -3936,13 +3944,15 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
 	return features;
 }
 
-netdev_features_t netif_skb_features(struct sk_buff *skb)
+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
@@ -3965,7 +3975,7 @@ netdev_features_t netif_skb_features(struct sk_buff *skb)
 
 	return harmonize_features(skb, features);
 }
-EXPORT_SYMBOL(netif_skb_features);
+EXPORT_SYMBOL(__netif_skb_features);
 
 static int xmit_one(struct sk_buff *skb, struct net_device *dev,
 		    struct netdev_queue *txq, bool more)
-- 
2.47.3