Hi Alex,
On 16/09/14 21:07, Alexander Aring wrote:
> 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"?
An integer that either contains an error code or 0 that process_data
would set as process_data is now IPHC decompression.
> - Alex
- Martin.
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