[dpdk-dev] [PATCH] net: introduce big and little endian types

[Ananyev, Konstantin]

> -----Original Message-----
> From: Nélio Laranjeiro [mailto:nelio.laranjeiro at 6wind.com]
> Sent: Tuesday, December 6, 2016 4:28 PM
> To: Morten Brørup <mb at smartsharesystems.com>
> Cc: Wiles, Keith <keith.wiles at intel.com>; Ananyev, Konstantin <konstantin.ananyev at intel.com>; Richardson, Bruce
> <bruce.richardson at intel.com>; dev at dpdk.org; Olivier Matz <olivier.matz at 6wind.com>; Lu, Wenzhuo <wenzhuo.lu at intel.com>; Adrien
> Mazarguil <adrien.mazarguil at 6wind.com>
> Subject: Re: [dpdk-dev] [PATCH] net: introduce big and little endian types
> 
> Hi all,
> 
> On Tue, Dec 06, 2016 at 04:34:07PM +0100, Morten Brørup wrote:
> > Hi all,
> >
> > Being a big fan of strong typing, I really like the concept of
> > explicit endian types. Especially if type mismatches can be caught at
> > compile time.
> 
> +1,
> 
> > However, I think it is too late! That train left the station when the
> > rest of the world - including libraries and headers that might be
> > linked with a DPDK application - decided to use implicit big endian
> > types for network protocols, and has been doing so for decades. And,
> > with all respect, I don't think the DPDK community has the momentum
> > required to change this tradition outside the community.
> 
> I don't think, those types can be use from now on to help new API to
> expose explicitly the type they are handling.  For older ones, it can
> come in a second step, even if there are not so numerous.  Only few of
> them touches the network types.
> 
> > Furthermore: If not enforced throughout DPDK (and beyond), it might
> > confuse more than it helps.
> 
> The current situation is more confusing,  nobody at any layer can rely
> on a precise information, at each function entry we need to verify if
> the callee has already handled the job.  The only solution is to browse
> the code to have this information.
> 
> Think about any function manipulating network headers (like flow director
> or rte_flow) from the API down to the PMD, it may take a lot of time to
> know at the end if the data is CPU or network ordered, with those types
> it takes less than a second.

Hmm, suppose I have such piece of code:

struct ipv4_hdr iph;
iph.total_length = val0;
iph.packet_id = val1;
...
iph.dst_addr = valn;

hton_whole_ipv4_hdr_at_once(&iph);

How I suppose to indicate via these new types that 
hton_whole_ipv4_hdr_at_once() expects ipv4_hdr fields in host byte order?
Other than just putting it into the doc?
Konstantin