From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bruce Richardson Subject: Re: [PATCH] net: introduce big and little endian types Date: Tue, 6 Dec 2016 13:30:57 +0000 Message-ID: <20161206133057.GA15416@bricha3-MOBL3.ger.corp.intel.com> References: <2601191342CEEE43887BDE71AB9772583F0E3F68@irsmsx105.ger.corp.intel.com> <20161205120603.GL21794@autoinstall.dev.6wind.com> <2601191342CEEE43887BDE71AB9772583F0E4632@irsmsx105.ger.corp.intel.com> <20161206115502.GA12224@bricha3-MOBL3.ger.corp.intel.com> <20161206131416.GR21794@autoinstall.dev.6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: "Ananyev, Konstantin" , "dev@dpdk.org" , Olivier Matz , "Lu, Wenzhuo" , Adrien Mazarguil To: =?iso-8859-1?Q?N=E9lio?= Laranjeiro Return-path: Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by dpdk.org (Postfix) with ESMTP id EAD4E2BB3 for ; Tue, 6 Dec 2016 14:31:01 +0100 (CET) Content-Disposition: inline In-Reply-To: <20161206131416.GR21794@autoinstall.dev.6wind.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 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