netdev - [SC92031] [BUG-FIX] [Patch 1/1]: Revert use of skb

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Message-ID: <20080502202940.GA5116@gerrit.erg.abdn.ac.uk>
Date:	Fri, 2 May 2008 21:29:40 +0100
From:	Gerrit Renker <gerrit@....abdn.ac.uk>
To:	davem@...emloft.net, netdev@...r.kernel.org
Cc:	shemminger@...tta.com
Subject: [SC92031] [BUG-FIX] [Patch 1/1]: Revert use of skb_padto

[SC92031]: Revert use of skb_padto (does not update skb->len)

This reverts use of skb_padto() introduced in 

 commit 26a17b7bbb36a8552d531bc1ad08472fb5aa3007
 Date:   Wed Apr 2 10:11:11 2008 -0700
 sc92031: start transmit return value bugfix

The padto does not work because the driver code evaluates `len' later on
and there are cases where skb->len is not updated accordingly.

This was observed with ARP frames (skb->len = 42 bytes, !skb_cloned(),
skb_tailroom = 84 bytes). Then in skb_pad(), the first condition is true,
where skb->len is not updated. As a consequence, the driver uses 42 bytes
instead of the 60 bytes, and the ARP frame never makes it onto the wire.

Signed-off-by: Gerrit Renker <gerrit@....abdn.ac.uk>
---
 sc92031.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/net/sc92031.c
+++ b/drivers/net/sc92031.c
@@ -953,9 +953,6 @@ static int sc92031_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	unsigned entry;
 	u32 tx_status;
 
-	if (skb_padto(skb, ETH_ZLEN))
-		return NETDEV_TX_OK;
-
 	if (unlikely(skb->len > TX_BUF_SIZE)) {
 		dev->stats.tx_dropped++;
 		goto out;
@@ -975,6 +972,11 @@ static int sc92031_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	skb_copy_and_csum_dev(skb, priv->tx_bufs + entry * TX_BUF_SIZE);
 
 	len = skb->len;
+	if (unlikely(len < ETH_ZLEN)) {
+		memset(priv->tx_bufs + entry * TX_BUF_SIZE + len,
+				0, ETH_ZLEN - len);
+		len = ETH_ZLEN;
+	}
 
 	wmb();
 


The University of Aberdeen is a charity registered in Scotland, No SC013683.

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