Re: [PATCH v4 bluetooth] 6lowpan: fix incorrect return values in lowpan_rcv

[Alexander Aring <alex.aring@gmail.com>]

On Tue, Sep 16, 2014 at 08:53:06PM +0100, Martin Townsend wrote:
...
> >I make another c example, hopeful more correct than the last one:
> >
> >char *foo(char *skb)
> >{
> >         char *new;
> >
> >         if (some_error_before_consume)
> >                 return ERR_PTR(-EINVAL); /* here we need to do a free(skb) */
> >
> >         /* UDP expand */
> >         new = expand(skb, 16);
s/16/8 , argl, doesn't matter was only an example. :-)

> >         if (!new)
> >                 return ERR_PTR(-ENOMEM);
> >         consume(skb); /* parameter skb becomes dangling pointer */
> >         skb = new; /* doesn't rescue it, it is different than skb from caller function
> >                       at this point, the skb_inout had rescue it, because it was a pointer
> >                       of pointer */
> >
> >         /* IPv6 expand */
> >         new = expand(skb, 40);
> >         if (!new) /* some error after a consume(skb), will crash at drop_skb label */
> >                 return ERR_PTR(-ENOMEM);
> >         consume(skb);
> >         skb = new;
> >
> >         return skb;
> >}
> I see the problem now, once the skb has been copied and then an error occurs
> you have to return the error and the skb has been lost.  Would using the
> skb->cb to store decompress status get around this problem?

mhhh, complicated... on 802.15.4 6LoWPAN we use the control block
information for fragmentation information. I don't know right now if we
get trouble when we add the "uncompression on the fly when FRAG1 was
received".

What exactly do you mean with "decompress status"?

- Alex