Re: [dpdk-dev] [PATCH RFC] mbuf/ip_frag: Move mbuf chaining to common code

["Simon Kågström" <simon.kagstrom@netinsight.net>]

On 2015-09-07 11:35, Olivier MATZ wrote:

>> Wonder why do we need to do that?
>> Probably head mbuf is out of space and want to expand it using pktmbuf_chain()?
>> So in that case seems logical:
>> 1) allocate new mbuf (it's pkt_len will be 0)
>> b) call pktmbuf_chain()
> 
> By experience, having empty segments in the middle of a mbuf
> chain is problematic (functions getting ptr at offsets, some pmds
> or hardware may behave badly), I wanted to avoid that risk.
> 
> Now, the use-case you described is legitimate. Another option would
> be to have another function pktmbuf_append_new(m) that returns a new
> mbuf that is already chained to the other.

I see with that method in that you have to remember to actually update
pkt_len in the head buffer when chaining an empty mbuf. Anyway, to
disallow this behavior should probably not be the responsibility of
rte_pktmbuf_chain(), so I'm fine with leaving the check out.

// Simon