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

Ananyev, Konstantin konstantin.ananyev at intel.com
Tue Dec 6 13:41:00 CET 2016



> -----Original Message-----
> From: Richardson, Bruce
> Sent: Tuesday, December 6, 2016 11:55 AM
> To: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Cc: Nélio Laranjeiro <nelio.laranjeiro at 6wind.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
> 
> 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.

Ok, so where do you believe we should draw a line?
Why let say inside lib/librte_net people should use these typedefs, but
inside drivers/net/ixgbe they don't?
 
> 
> 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.

Not sure I understand you here.
Could you possibly provide some example?

Konstantin


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