netdev - Re: [PATCH v2 net-next] net: cleanup and document skb fclone layout

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Message-ID: <1412162524.16704.53.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 01 Oct 2014 04:22:04 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vijay Subramanian <subramanian.vijay@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] net: cleanup and document skb fclone layout

On Wed, 2014-10-01 at 00:38 -0700, Vijay Subramanian wrote:
> >         case SKB_FCLONE_CLONE:
> > -               fclone_ref = (atomic_t *) (skb + 1);
> > -               other = skb - 1;
> > +               fclones = container_of(skb, struct sk_buff_fclones, skb2);
> >
> >                 /* The clone portion is available for
> >                  * fast-cloning again.
> >                  */
> >                 skb->fclone = SKB_FCLONE_UNAVAILABLE;
> >
> 
> It looks like SKB_FCLONE_UNAVAILABLE has overloaded use depending on
> whether we are referring to skb allocated from head_cache or from
> fclone_cache. In the former case, it means this skb cannot be cloned
> i.e.(clone is unavailable) but in latter case, it means clone is free
> to be used.
> This overleading is confusing as seen in the comment in snippet above.
> 
> Should we add  something like SKB_CLONE_FREE for the second case that
> indicates that clone is free for use.?  I can send a patch if it makes
> sense..

FCLONE_UNAVAILABLE always had two meanings, one for a normal skb telling
there is no fclone companion, one for the companion telling he is free.

It would be indeed clear to have SKB_CLONE_FREE for the companion.



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