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

[Nélio Laranjeiro]

Hi Konstantin, Bruce,

On Tue, Dec 06, 2016 at 11:55:02AM +0000, Bruce Richardson wrote:
> On Tue, Dec 06, 2016 at 11:23:42AM +0000, Ananyev, Konstantin wrote:
> > Hi Neilo,
> > 
> > 
> > Hi Neilo,
> > > > >
> > > > > This commit introduces new rte_{le,be}{16,32,64}_t types and updates
> > > > > rte_{le,be,cpu}_to_{le,be,cpu}_*() and network header structures
> > > > > accordingly.
> > > > >
> > > > > Specific big/little endian types avoid uncertainty and conversion mistakes.
> > > > >
> > > > > No ABI change since these are simply typedefs to the original types.
> > > >
> > > > It seems like quite a lot of changes...
> > > > Could you probably explain what will be the benefit in return?
> > > > Konstantin
> > > 
> > > Hi Konstantin,
> > > 
> > > The benefit is to provide documented byte ordering for data types
> > > software is manipulating to determine when network to CPU (or CPU to
> > > network) conversion must be performed.
> > 
> > Ok, but is it really worth it?
> > User can still make a mistake and forget to call ntoh()/hton() at some particular place.
> > From other side most people do know that network protocols headers are usually in BE format. 
> > I would understand the effort, if we'll have some sort of tool that would do some sort of static code analysis
> > based on these special types or so.
> > Again, does it mean that we should go and change uint32_t to rte_le_32 inside all Intel PMDs
> > (and might be  in some others too) to be consistent?
> > Konstantin
> > 
> 
> I actually quite like this patch as I think it will help make things
> clear when the user is possibly doing something wrong. I don't think we
> need to globally change all PMDs to use the types, though.

I agree, at least APIs should use this, PMDs can do as they want.

> One thing I'm wondering though, is if we might want to take this
> further. For little endian environments, we could define the big endian
> types as structs using typedefs, and similarly the le types on be
> platforms, so that assigning from the non-native type to the native one
> without a transformation function would cause a compiler error.
> 
> /Bruce

If I understand you correctly, this will break hton like functions which
expects an uint*_t not a structure.

-- 
Nélio Laranjeiro
6WIND