On Tue, Dec 06, 2016 at 02:14:17PM +0100, Nélio Laranjeiro wrote:
> 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.
>
Yes, it would break the standard ones, which is the downside of doing
this. We could try "fixing" that with a macro, but that too won't always
work. It's a question of whether the additional safety given by having
the compiler flag an error on an invalid assignment, e.g. of a big-endian
value to a native-little endian value, is worth having to change existing
code using htons to use e.g. rte_htons. Given the cost of changing a lot of
existing code, it may just not be worthwhile, but I thought I'd suggest
it anyway as a way of even better guaranteeing endian-ness safety.
/Bruce
