From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by dpdk.space (Postfix) with ESMTP id 07961A0096 for ; Thu, 6 Jun 2019 15:35:48 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id E0C641B95A; Thu, 6 Jun 2019 15:35:47 +0200 (CEST) Received: from smtp.tuxdriver.com (charlotte.tuxdriver.com [70.61.120.58]) by dpdk.org (Postfix) with ESMTP id 3257F1B958 for ; Thu, 6 Jun 2019 15:35:47 +0200 (CEST) Received: from cpe-2606-a000-111b-405a-0-0-0-162e.dyn6.twc.com ([2606:a000:111b:405a::162e] helo=localhost) by smtp.tuxdriver.com with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.63) (envelope-from ) id 1hYsYJ-0002v7-S7; Thu, 06 Jun 2019 09:35:42 -0400 Date: Thu, 6 Jun 2019 09:35:03 -0400 From: Neil Horman To: Jerin Jacob Kollanukkaran Cc: Bruce Richardson , "dev@dpdk.org" , Thomas Monjalon Message-ID: <20190606133503.GB29521@hmswarspite.think-freely.org> References: <20190525184346.27932-1-nhorman@tuxdriver.com> <20190605164541.GH1550@bricha3-MOBL.ger.corp.intel.com> <20190605181108.GC554@hmswarspite.think-freely.org> <20190606113422.GA29521@hmswarspite.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.3 (2019-02-01) X-Spam-Score: -2.9 (--) X-Spam-Status: No Subject: Re: [dpdk-dev] [EXT] [RFC PATCH 0/2] introduce __rte_internal tag X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list 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 Thu, Jun 06, 2019 at 12:04:57PM +0000, Jerin Jacob Kollanukkaran wrote: > > -----Original Message----- > > From: Neil Horman > > Sent: Thursday, June 6, 2019 5:04 PM > > To: Jerin Jacob Kollanukkaran > > Cc: Bruce Richardson ; dev@dpdk.org; > > Thomas Monjalon > > Subject: Re: [EXT] [RFC PATCH 0/2] introduce __rte_internal tag > > > > On Thu, Jun 06, 2019 at 09:44:52AM +0000, Jerin Jacob Kollanukkaran wrote: > > > > -----Original Message----- > > > > From: Neil Horman > > > > Sent: Wednesday, June 5, 2019 11:41 PM > > > > To: Bruce Richardson > > > > Cc: Jerin Jacob Kollanukkaran ; dev@dpdk.org; > > > > Thomas Monjalon > > > > Subject: Re: [EXT] [RFC PATCH 0/2] introduce __rte_internal tag > > > > > > > > On Wed, Jun 05, 2019 at 05:45:41PM +0100, Bruce Richardson wrote: > > > > > On Wed, Jun 05, 2019 at 04:24:09PM +0000, Jerin Jacob > > > > > Kollanukkaran > > > > wrote: > > > > > > > -----Original Message----- > > > > > > > From: Neil Horman > > > > > > > Sent: Sunday, May 26, 2019 12:14 AM > > > > > > > To: dev@dpdk.org > > > > > > > Cc: Neil Horman ; Jerin Jacob > > > > > > > Kollanukkaran ; Bruce Richardson > > > > > > > ; Thomas Monjalon > > > > > > > > > > > > > > Subject: [EXT] [RFC PATCH 0/2] introduce __rte_internal tag > > > > > > > > > > > > > > Hey- > > > > > > > Based on our recent conversations regarding the use of > > > > > > > symbols only meant for internal dpdk consumption (between dpdk > > > > > > > libraries), this is an idea that I've come up with that I'd > > > > > > > like to get some feedback on > > > > > > > > > > > > > > Summary: > > > > > > > 1) We have symbols in the DPDK that are meant to be used > > > > > > > between DPDK libraries, but not by applications linking to > > > > > > > them > > > > > > > 2) We would like to document those symbols in the code, so as > > > > > > > to note them clearly as for being meant for internal use only > > > > > > > 3) Linker symbol visibility is a very coarse grained tool, and > > > > > > > so there is no good way in a single library to mark items as > > > > > > > being meant for use only by other DPDK libraries, at least not > > > > > > > without some extensive runtime checking > > > > > > > > > > > > > > > > > > > > > Proposal: > > > > > > > I'm proposing that we introduce the __rte_internal tag. From > > > > > > > a coding standpoint it works a great deal like the > > > > > > > __rte_experimental tag in that it expempts the tagged symbol > > > > > > > from ABI constraints (as the only users should be represented > > > > > > > in the DPDK build environment). Additionally, the > > > > > > > __rte_internal macro resolves differently based on the > > > > > > > definition of the BUILDING_RTE_SDK flag (working under the > > > > > > > assumption that said flag should only ever be set if we are > > > > > > > actually building DPDK libraries which will make use of > > > > > > > internal calls). If the BUILDING_RTE_SDK flag is set > > > > > > > __rte_internal resolves to __attribute__((section > > > > > > > "text.internal)), placing it in a special text section which > > > > > > > is then used to validate that the the symbol appears in the > > > > > > > INTERNAL section of the corresponding library version map). > > > > > > > If BUILDING_RTE_SDK is not set, then __rte_internal resolves > > > > > > > to > > > > __attribute__((error("..."))), which causes any caller of the tagged > > > > function to throw an error at compile time, indicating that the > > > > symbol is not available for external use. > > > > > > > > > > > > > > This isn't a perfect solution, as applications can still hack > > > > > > > around it of course, > > > > > > > > > > > > I think, one way to, avoid, hack around could be to, > > > > > > > > > > > > 1) at config stage, create a random number for the build > > > > > > 2) introduce RTE_CALL_INTERNAL macro for calling internal > > > > > > function, compare the generated random number for allowing the > > > > > > calls to make within the library. i.e leverage the fact that > > > > > > external library would never know the random number generated > > > > > > for the DPDK build > > > > and internal driver code does. > > > > > > > > > > > Do we really need to care about this. If have some determined > > > > > enough to hack around our limitations, then they surely know that > > > > > they have an unsupported configuration. We just need to protect > > > > > against inadvertent use of internals, IMHO. > > > > > > > > > I agree, I too had thought about doing some sort of internal runtime > > > > checking to match internal only symbols, such that they were only > > > > accessable by internally approved users, but it started to feel like a great > > deal of overhead. > > > > Its a good idea for a general mechanism I think, but I believe the > > > > value here is more to internally document which apis we want to mark > > > > as being for internal use only, and create a lightweight roadblock > > > > at build time to catch users inadvertently using them. Determined > > > > users will get around anything, and theres not much we can do to stop > > them. > > > > > > I agree too. IMHO, Simply having following items would be enough > > > > > > 1) Avoid exposing the internal function prototype through public > > > header files > > > 2) Add @internal to API documentation > > > 3) Just decide the name space for internal API for tooling(i.e not > > > start with rte_ or so) Using objdump scheme to detect internal functions > > requires the the library to build prior to run the checkpatch. > > > > > > > No, I'm not comfortable with that approach, and I've stated why: > > 1) Not exposing the functions via header files is a fine start > > > > 2) Adding internal documentation is also fine, but does nothing to correlate > > the code implementing those functions to the documentation. Its valuable > > to have a tag on a function identifying it as internal only. > > > > 3) Using naming conventions to separate internal only from non-internal > > functions is a vague approach, requiring future developers to be cogniscent > > of the convention and make the appropriate naming choices. It also implicitly > > restricts the abliity for future developers to make naming changes in conflict > > with that convention > > Enforcing the naming convention can be achieved through tooling as well. > Sure, but why enforce any function naming at all, when you don't have to. > > > > 4) Adding a tag like __rte_internal creates an interlock whereby, not only are > > internal functions excused from ABI constraints, but forces developers to > > intentionally mark their internal functions as being internal in the code, which > > is beneficial to clarlity of understanding during the development process. > > No issues in adding __rte_internal. But, I am against current implementaion, > Ie. adding objdump dependency That dependency already exists for the __rte_external flag > to checkpatch i.e developer has to build the library first so that checkpatch can > can know, Is it belongs to internal section or not? > What developer is running checkpatch/posting patches without first building their changes? > > > > 5) Adding a tag like __rte_internal is explicit, and allows developers to use a > > single header file instead of multiple header files if they so choose > > > > We went through this with experimental symbols as well[1], and it just > > makes more sense to me to clearly document in the code what constitutes > > an internal symbol rather than relying on naming conventions and hoping > > that developers read the documentation before exporting a symbol > > publically. > > > > > > [1] https://mails.dpdk.org/archives/dev/2017-December/083828.html > > > > > > > > If we really wanted to go down that road, we could use a mechainsm > > > > simmilar to the EXPORT_SYMBOL / EXPORT_SYMBOL_GPL infrastructure > > > > that the kernel uses, but that would required building our own > > > > custom linker script, which seems like overkill here. > > > > > > > > Best > > > > Neil > > > > > > > > > /Bruce > > > > > > > > >