[dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and nbsegments

[Morten Brørup]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Tuesday, July 11, 2017 5:06 PM
> To: Morten Brørup
> Cc: dev at dpdk.org; Wiles, Keith; Olivier Matz; Wang, Zhihong; Yuanhan
> Liu; Ananyev, Konstantin; Richardson, Bruce; Chilikin, Andrey; Jan
> Blunck; nelio.laranjeiro at 6wind.com; arybchenko at solarflare.com;
> jerin.jacob at caviumnetworks.com
> Subject: Re: [dpdk-dev] [PATCH v2 6/8] mbuf: use 2 bytes for port and
> nbsegments
> 
> 11/07/2017 15:30, Morten Brørup:
> > Morten Brørup wrote:
> > > Olivier Matz wrote:
> > > > As I said in a previous message, I think a good first step would
> > > > be to introduce a typedef for the port number:
> rte_eth_port_num_t.
> > > > It can still be uint8_t for now, and can be switched to 16 bits
> in
> > > > one step when everyone uses this new type.
> > >
> > > I think that DPDK follows the Linux tradition of exposing the
> > > variable types, as opposed to hiding them behind typedefs. This has
> > > the unfortunate consequence that when a variable type changes, it
> > > has to be changed everywhere.
> > >
> > > Introducing a rte_eth_port_num_t will require changing the same
> > > files at the same locations everywhere, so not even as a temporary
> > > solution will it be beneficial.
> [...]
> > What I was trying to communicate with my long argument about type
> definitions was: When the type changed from 8 bit to 16 bit, the type
> needs to change from uint8_t to uint16_t everywhere too, including in
> the ethdev APIs.
> >
> > Don't start breaking coding conventions here by hiding the type of
> this variable.
> 
> So, Morten, you are against the typedef, right?
> Because we need to change it everywhere anyway, right?
> 
> Note: I have no strong opinion.

I'm against the typedef because it would break convention, and I'm a strong proponent of conventions. In other projects, I'm all for typedefs, virtual classes, inheritance etc., but DPDK follows the Linux convention of not hiding simple types.

We need to change it from uint8_t everywhere, regardless what we change it to. (But if we need to change it again sometime in the future, then a typedef will save us next time.)

However, if we change the convention and start hiding simple types, they still need the rte_ prefix regardless if they are popular or obscure types. Even struct rte_mbuf has the rte_ prefix, and I consider that a very popular type. If so, rte_port_t would be a good name for this type.

My preference: Follow convention and change it to uint16_t everywhere.

Med venlig hilsen / kind regards
- Morten Brørup