linux-kernel - [PATCH net-next 3/3] net: dsa: trailer: don't allocate additional memory for padding/tagging

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Message-ID: <20201016200226.23994-4-ceggers@arri.de>
Date:   Fri, 16 Oct 2020 22:02:26 +0200
From:   Christian Eggers <ceggers@...i.de>
To:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Kurt Kanzenbach <kurt@...utronix.de>
CC:     "David S . Miller" <davem@...emloft.net>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Christian Eggers <ceggers@...i.de>
Subject: [PATCH net-next 3/3] net: dsa: trailer: don't allocate additional memory for padding/tagging

The caller (dsa_slave_xmit) guarantees that the frame length is at least
ETH_ZLEN and that enough memory for tail tagging is available.

Signed-off-by: Christian Eggers <ceggers@...i.de>
---
 net/dsa/tag_trailer.c | 31 ++-----------------------------
 1 file changed, 2 insertions(+), 29 deletions(-)

diff --git a/net/dsa/tag_trailer.c b/net/dsa/tag_trailer.c
index 3a1cc24a4f0a..5b97ede56a0f 100644
--- a/net/dsa/tag_trailer.c
+++ b/net/dsa/tag_trailer.c
@@ -13,42 +13,15 @@
 static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct dsa_port *dp = dsa_slave_to_port(dev);
-	struct sk_buff *nskb;
-	int padlen;
 	u8 *trailer;
 
-	/*
-	 * We have to make sure that the trailer ends up as the very
-	 * last 4 bytes of the packet.  This means that we have to pad
-	 * the packet to the minimum ethernet frame size, if necessary,
-	 * before adding the trailer.
-	 */
-	padlen = 0;
-	if (skb->len < 60)
-		padlen = 60 - skb->len;
-
-	nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);
-	if (!nskb)
-		return NULL;
-	skb_reserve(nskb, NET_IP_ALIGN);
-
-	skb_reset_mac_header(nskb);
-	skb_set_network_header(nskb, skb_network_header(skb) - skb->head);
-	skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head);
-	skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));
-	consume_skb(skb);
-
-	if (padlen) {
-		skb_put_zero(nskb, padlen);
-	}
-
-	trailer = skb_put(nskb, 4);
+	trailer = skb_put(skb, 4);
 	trailer[0] = 0x80;
 	trailer[1] = 1 << dp->index;
 	trailer[2] = 0x10;
 	trailer[3] = 0x00;
 
-	return nskb;
+	return skb;
 }
 
 static struct sk_buff *trailer_rcv(struct sk_buff *skb, struct net_device *dev,
-- 
Christian Eggers
Embedded software developer

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