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

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Date:	Wed, 20 Jul 2011 12:36:31 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Ben Greear <greearb@...delatech.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 Wed, Jul 20, 2011 at 09:33:20AM -0700, Ben Greear wrote:
> 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
> 
Understood, thank you Ben.
Neil

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