netdev - Re: [PATCH V2 2/3] net: dsa: ksz: Factor out common tag code

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Date:   Sat, 15 Dec 2018 01:39:08 +0100
From:   Marek Vasut <marex@...x.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, f.fainelli@...il.com,
        Tristram Ha <Tristram.Ha@...rochip.com>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH V2 2/3] net: dsa: ksz: Factor out common tag code

On 12/14/2018 09:11 PM, Andrew Lunn wrote:
> On Fri, Dec 14, 2018 at 02:30:35PM +0100, Marek Vasut wrote:
>> On 12/14/2018 10:05 AM, Andrew Lunn wrote:
>>>> +static struct sk_buff *ksz_common_xmit(struct sk_buff *skb,
>>>> +				       struct net_device *dev, int len)
>>>>  {
>>>> -	struct dsa_port *dp = dsa_slave_to_port(dev);
>>>>  	struct sk_buff *nskb;
>>>>  	int padlen;
>>>> -	u8 *tag;
>>>>  
>>>>  	padlen = (skb->len >= ETH_ZLEN) ? 0 : ETH_ZLEN - skb->len;
>>>>  
>>>> -	if (skb_tailroom(skb) >= padlen + KSZ_INGRESS_TAG_LEN) {
>>>> +	if (skb_tailroom(skb) >= padlen + len) {
>>>>  		/* Let dsa_slave_xmit() free skb */
>>>>  		if (__skb_put_padto(skb, skb->len + padlen, false))
>>>>  			return NULL;
>>>
>>> Hi Marek
>>
>> Hi,
>>
>>> This can return NULL.
>>>
>>>> +static struct sk_buff *ksz9477_xmit(struct sk_buff *skb,
>>>> +				    struct net_device *dev)
>>>> +{
>>>> +	struct dsa_port *dp = dsa_slave_to_port(dev);
>>>> +	struct sk_buff *nskb;
>>>> +	u16 *tag;
>>>> +	u8 *addr;
>>>> +
>>>> +	nskb = ksz_common_xmit(skb, dev, KSZ9477_INGRESS_TAG_LEN);
>>>
>>> So here you need to check for NULL
>>
>> What do we do if the xmit returns NULL ?
> 
> Return NULL to the caller. There are comments which explain this:

Ahh ... right, of course.

> static netdev_tx_t dsa_slave_xmit(struct sk_buff *skb, struct net_device *dev)
> {
> [snip]
>         /* Transmit function may have to reallocate the original SKB,
>          * in which case it must have freed it. Only free it here on error.
>          */
>         nskb = p->xmit(skb, dev);
>         if (!nskb) {
>                 kfree_skb(skb);
>                 return NETDEV_TX_OK;
>         }
> 
> 	Andrew
> 


-- 
Best regards,
Marek Vasut