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

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Message-ID: <20110720153958.GE12349@hmsreliant.think-freely.org>
Date:	Wed, 20 Jul 2011 11:39:58 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Greear <greearb@...delatech.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 05:30:17PM +0200, Eric Dumazet wrote:
> Le mercredi 20 juillet 2011 à 11:18 -0400, Neil Horman a écrit :
> > 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;
> > +
> 
> Well, the general idea was to intercept the "clone_skb XXX" command and
> cap XXX to 0 for said devices.
> 
Isn't that exactly what this does?  Disallows a user from issuing the cone_skb
command in a pktgen script if the underlying driver can't support the sharing of
skbs.

> So some admin can still use pktgen without clone_skb stuff.
> 
Yes. this doesn't preclude that unless you see something I dont
Neil

> 
> 
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