> > On Tue, Dec 06, 2016 at 12:41:00PM +0000, Ananyev, Konstantin wrote: > > > > > > > -----Original Message----- > > > From: Richardson, Bruce > > > Sent: Tuesday, December 6, 2016 11:55 AM > > > To: Ananyev, Konstantin <konstantin.anan...@intel.com> > > > Cc: Nélio Laranjeiro <nelio.laranje...@6wind.com>; dev@dpdk.org; Olivier > > > Matz <olivier.m...@6wind.com>; Lu, Wenzhuo > > > <wenzhuo...@intel.com>; Adrien Mazarguil <adrien.mazarg...@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? > > Because those are not public APIs. It would be great if driver writers > used the typedefs, but I don't think it should be mandatory.
Ok, so only public API would have to use these typedefs when appropriate, correct? I still think that the effort to make these changes and keep this rule outweighs the benefit, but ok if everyone else think it is useful - I wouldn't object too much. > > > > > > > > > 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? > > > typedef struct { > short val; > } rte_be16_t; Hmm, so: uint32_t x = rte_be_to_cpu_32(1); would suddenly stop compiling? That definitely looks like an ABI breakage to me. Konstantin > > That way if you try to assign a value of type rte_be16_t to a uint16_t > variable you'll get a compiler error, unless you use an appropriate > conversion function. In short, it changes things from not just looking > wrong - which is the main purpose of Neilo's patchset - to actually > making it incorrect from the compiler's point of view too. > > /Bruce