From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62C58C4346E for ; Thu, 24 Sep 2020 08:40:25 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F289523787 for ; Thu, 24 Sep 2020 08:40:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F289523787 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=8bytes.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 6FA462E0E9; Thu, 24 Sep 2020 08:40:24 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Ka2uWFrh3oDB; Thu, 24 Sep 2020 08:40:23 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 2AA1220113; Thu, 24 Sep 2020 08:40:23 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1ACCDC0889; Thu, 24 Sep 2020 08:40:23 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id F0B78C0051 for ; Thu, 24 Sep 2020 08:40:21 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id E4168874D8 for ; Thu, 24 Sep 2020 08:40:21 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id POcTssMFoTN9 for ; Thu, 24 Sep 2020 08:40:20 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from theia.8bytes.org (8bytes.org [81.169.241.247]) by hemlock.osuosl.org (Postfix) with ESMTPS id 94F06874D7 for ; Thu, 24 Sep 2020 08:40:20 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id D53C3295; Thu, 24 Sep 2020 10:40:17 +0200 (CEST) Date: Thu, 24 Sep 2020 10:40:16 +0200 From: Joerg Roedel To: Jacob Pan Subject: Re: [PATCH v9 3/7] iommu/uapi: Introduce enum type for PASID data format Message-ID: <20200924084015.GC27174@8bytes.org> References: <1599861476-53416-1-git-send-email-jacob.jun.pan@linux.intel.com> <1599861476-53416-4-git-send-email-jacob.jun.pan@linux.intel.com> <20200918094450.GP31590@8bytes.org> <20200918101108.672c2f5a@jacob-builder> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200918101108.672c2f5a@jacob-builder> User-Agent: Mutt/1.10.1 (2018-07-13) Cc: "Tian, Kevin" , Jacob Pan , Raj Ashok , Jonathan Corbet , Jean-Philippe Brucker , iommu@lists.linux-foundation.org, LKML , Alex Williamson , Wu Hao , David Woodhouse , Yi Sun X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi Jacob, On Fri, Sep 18, 2020 at 10:11:08AM -0700, Jacob Pan wrote: > On Fri, 18 Sep 2020 11:44:50 +0200, Joerg Roedel wrote: > > > On Fri, Sep 11, 2020 at 02:57:52PM -0700, Jacob Pan wrote: > > > There can be multiple vendor-specific PASID data formats used in UAPI > > > structures. This patch adds enum type with a last entry which makes > > > range checking much easier. > > > > But it also makes it much easier to screw up the numbers (which are ABI) > > by inserting a new value into the middle. I prefer defines here, or > > alternativly BUILD_BUG_ON() checks for the numbers. > > > I am not following, the purpose of IOMMU_PASID_FORMAT_LAST *is* for > preparing the future insertion of new value into the middle. > The checking against IOMMU_PASID_FORMAT_LAST is to protect ABI > compatibility by making sure that out of range format are rejected in all > versions of the ABI. But with the enum you could have: enum { VTD_FOO, SMMU_FOO, LAST, }; which makes VTD_FOO==0 and SMMU_FOO==1, and when in the next version someone adds: enum { VTD_FOO, VTD_BAR, SMMU_FOO, LAST, }; then SMMU_FOO will become 2 and break ABI. So I'd like to have this checked somewhere. Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu