[PATCH RFC net-next 2/6] net: build gso segs in multi release time SO_TXTIME

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

From: Willem de Bruijn <willemb@google.com>

When sending multiple segments per interval and the device supports
hardware segmentation, build one GSO segment per interval.

Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 net/core/dev.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5058083375fb..05f538f0f631 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3379,7 +3379,9 @@ EXPORT_SYMBOL(__skb_gso_segment);
 
 struct sk_buff *skb_gso_segment_txtime(struct sk_buff *skb)
 {
+	const netdev_features_t hw_features = NETIF_F_GSO_UDP_L4;
 	int mss_per_ival, mss_in_cur_ival;
+	u16 gso_size_orig, gso_segs_orig;
 	struct sk_buff *segs, *seg;
 	struct skb_shared_info *sh;
 	u64 step_ns, tstamp;
@@ -3401,13 +3403,27 @@ struct sk_buff *skb_gso_segment_txtime(struct sk_buff *skb)
 	if (sh->gso_segs <= mss_per_ival)
 		return NULL;
 
+	/* update gso size and segs to build 1 GSO packet per ival */
+	gso_size_orig = sh->gso_size;
+	gso_segs_orig = sh->gso_segs;
+	if (mss_per_ival > 1 && skb->dev->features & hw_features) {
+		sh->gso_size *= mss_per_ival;
+		sh->gso_segs = DIV_ROUND_UP(sh->gso_segs, mss_per_ival);
+		mss_per_ival = 1;
+	}
+
 	segs = skb_gso_segment(skb, NETIF_F_SG | NETIF_F_HW_CSUM);
-	if (IS_ERR_OR_NULL(segs))
+	if (IS_ERR_OR_NULL(segs)) {
+		sh->gso_size = gso_size_orig;
+		sh->gso_segs = gso_segs_orig;
 		return segs;
+	}
 
 	mss_in_cur_ival = 0;
 
 	for (seg = segs; seg; seg = seg->next) {
+		unsigned int data_len, data_off;
+
 		seg->tstamp = tstamp & ~0xFF;
 
 		mss_in_cur_ival++;
@@ -3415,6 +3431,17 @@ struct sk_buff *skb_gso_segment_txtime(struct sk_buff *skb)
 			tstamp += step_ns;
 			mss_in_cur_ival = 0;
 		}
+
+		data_off = skb_checksum_start_offset(skb) +
+			   skb->csum_offset + sizeof(__sum16);
+		data_len = seg->len - data_off;
+
+		if (data_len > gso_size_orig) {
+			sh = skb_shinfo(seg);
+			sh->gso_type = skb_shinfo(skb)->gso_type;
+			sh->gso_size = gso_size_orig;
+			sh->gso_segs = DIV_ROUND_UP(data_len, gso_size_orig);
+		}
 	}
 
 	return segs;
-- 
2.27.0.278.ge193c7cf3a9-goog