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

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Message-ID: <CAHXqBFJhChXOpDOON-bz-DAkFUaggTYjwe6qjggb07Pf9bF8Vw@mail.gmail.com>
Date:	Wed, 20 Jul 2011 18:08:39 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Neil Horman <nhorman@...driver.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

W dniu 20 lipca 2011 17:40 użytkownik Neil Horman
<nhorman@...driver.com> napisał:
> 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?

I assumed you wanted to use netdev->features and I noticed priv_flags
just now. If the flag is supposed to be permanent then its fine by me.
Actually this makes me wonder if NETIF_F_LLTX and similar should get
moved to netdev->priv_flags.

Best Regards,
Michał Mirosław
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