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

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Message-ID: <20110720154057.GF12349@hmsreliant.think-freely.org>
Date:	Wed, 20 Jul 2011 11:40:57 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Michał Mirosław <mirqus@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	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 05:35:47PM +0200, Michał Mirosław wrote:
> 2011/7/20 Neil Horman <nhorman@...driver.com>:
> > 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;
> >
> 
> I would prefer that the flag be inclusive, i.e. it should mark drivers
> which can use shared skbs. And it might be better to clone the skb in
> case the flag is disabled to keep functionality working.
> 
Ok, I can agree with that.  But you're ok with the general approach?
Neil

> Best Regards,
> Michał Mirosław
> 
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