netdev - [PATCH] veth: Optionally pad packets to minimum Ethernet length

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Date:   Tue, 12 Dec 2017 08:13:11 -0800
From:   Ed Swierk <eswierk@...portsystems.com>
To:     netdev@...r.kernel.org
Cc:     Ed Swierk <eswierk@...portsystems.com>,
        Benjamin Warren <ben@...portsystems.com>,
        Keith Holleman <holleman@...portsystems.com>
Subject: [PATCH] veth: Optionally pad packets to minimum Ethernet length

Most physical Ethernet devices pad short packets to the minimum length
of 64 bytes (including FCS) on transmit. It can be useful to simulate
this behavior when debugging a problem that results from it (such as
incorrect L4 checksum calculation).

Padding is unnecessary for most applications so leave it off by
default. Enable padding only when the otherwise unused IFF_AUTOMEDIA
flag is set (e.g. by writing 0x5003 to flags in sysfs).

Signed-off-by: Ed Swierk <eswierk@...portsystems.com>
---
 drivers/net/veth.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index f5438d0978ca..292029bf4bb2 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -111,6 +111,12 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
 		goto drop;
 	}

+	if (unlikely(dev->flags & IFF_AUTOMEDIA)) {
+		/* if eth_skb_pad returns an error the skb was freed */
+		if (eth_skb_pad(skb))
+			goto drop;
+	}
+
 	if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) {
 		struct pcpu_vstats *stats = this_cpu_ptr(dev->vstats);

-- 
2.11.0