netdev - Re: [PATCH] pktgen: Clone skb to avoid corruption of skbs in ndo_start

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Date:	Wed, 20 Jul 2011 09:33:20 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	"David S. Miller" <davem@...emloft.net>, robert.olsson@....uu.se
Subject: Re: [PATCH] pktgen: Clone skb to avoid corruption of skbs in ndo_start_xmit
 methods

On 07/20/2011 08:18 AM, Neil Horman wrote:
> On Wed, Jul 20, 2011 at 06:24:15AM +0200, Eric Dumazet wrote:
>> Le mardi 19 juillet 2011 à 22:07 -0400, Neil Horman a écrit :
>>>>
>>> I think this is a good idea.  It lets pktgen dynamically make the clone/share
>>> decision dynamically and only impacts performance for those systems.
>>>
>>
>> Just let pktgen refuse to use clone_skb command for these devices.
>>
> copy that, This is by no means final, but what do you think of this?  If its
> agreeable to you, Ben, et al. I can add this to my local tree and start auditing
> all the drivers that may need to have the flag set.
>
> Regards
> Neil
>
>
> diff --git a/include/linux/if.h b/include/linux/if.h
> index 3bc63e6..ae904fe 100644
> --- a/include/linux/if.h
> +++ b/include/linux/if.h
> @@ -76,6 +76,7 @@
>   #define IFF_BRIDGE_PORT	0x4000		/* device used as bridge port */
>   #define IFF_OVS_DATAPATH	0x8000	/* device used as Open vSwitch
>   					 * datapath port */
> +#define IFF_CANT_SHARE_SKB	0x10000	/* Device can't share skbs in tx path */
>
>   #define IF_GET_IFACE	0x0001		/* for querying only */
>   #define IF_GET_PROTO	0x0002
> diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> index f76079c..bf6d88d 100644
> --- a/net/core/pktgen.c
> +++ b/net/core/pktgen.c
> @@ -1071,6 +1071,9 @@ static ssize_t pktgen_if_write(struct file *file,
>   		if (len<  0)
>   			return len;
>
> +		if (pkt_dev->priv_flags&  IFF_CANT_SHARE_SKB)
> +			return -EOPNOTSUPP;
> +
>   		i += len;
>   		pkt_dev->clone_skb = value;
>

Please only return an error if value > 1.

Also, if there is any place where user can configure pkt_dev,
you would want code there to check for the CANT_SHARE_SKB flag
and force clone_skb to zero if user changes to a different
device that cannot share skbs.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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