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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0EF90C433FE for ; Wed, 16 Nov 2022 16:05:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233087AbiKPQFK (ORCPT ); Wed, 16 Nov 2022 11:05:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230429AbiKPQFF (ORCPT ); Wed, 16 Nov 2022 11:05:05 -0500 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4629C2E9DC for ; Wed, 16 Nov 2022 08:05:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1668614705; x=1700150705; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=n9AN618bUNj13xisUH6R3r0HHk9xx57S07U0cpH9LJQ=; b=lZ9IHFT0J1YAw8eAnjtWtSCLVBgEh3hD8cfCUgJb00gfvOunPNQLua2i pLYR3juSB8U0j7TKv2g5J9upBkvrXi1Dfp5G7myvySOYlPuCN9Yw/JZ5S aNethwFzvNNyEkT1lRGtmCOdu1w0JT30KpdgNjj84ywZclKVPUWCNhHTb Zx/Y6OSmt8iMr68aC2PoiwfKuJiozj0K/gGntqQzNJmB89i4kaBqs1DJG I6jqGai+YICJNQhqXpy1hBzGH/jhJDzGarL2XTXb7/aroOG7ChBGtDFTi MeVmG2TARna4x/ktIEvRur2vAA/FFIIe+F4dvqjqs/yxiVHgmBkEJ23TO A==; X-IronPort-AV: E=McAfee;i="6500,9779,10533"; a="292973464" X-IronPort-AV: E=Sophos;i="5.96,167,1665471600"; d="scan'208";a="292973464" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Nov 2022 08:04:41 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10533"; a="590238725" X-IronPort-AV: E=Sophos;i="5.96,167,1665471600"; d="scan'208";a="590238725" Received: from smile.fi.intel.com ([10.237.72.54]) by orsmga003.jf.intel.com with ESMTP; 16 Nov 2022 08:04:39 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.96) (envelope-from ) id 1ovKty-00DD59-0o; Wed, 16 Nov 2022 18:04:38 +0200 Date: Wed, 16 Nov 2022 18:04:37 +0200 From: Andy Shevchenko To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, Fei Li , "Rafael J. Wysocki" Subject: Re: [PATCH v4 1/1] virt: acrn: Mark the uuid field as unused Message-ID: References: <20221116092254.66234-1-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 16, 2022 at 04:20:08PM +0100, Greg Kroah-Hartman wrote: > On Wed, Nov 16, 2022 at 03:29:31PM +0200, Andy Shevchenko wrote: > > On Wed, Nov 16, 2022 at 12:42:16PM +0100, Greg Kroah-Hartman wrote: > > > On Wed, Nov 16, 2022 at 11:22:54AM +0200, Andy Shevchenko wrote: ... > > > > - * @uuid: UUID of the VM. Pass to hypervisor directly. > > > > + * @uuid: Reserved (used to be UUID of the VM) > > > > > > If it's reserved, then don't you need to check for 0? > > > > Reserved in a way that it may content something we just don't care about. > > "reserved" in the kernel ioctls mean "must be 0 and we will test for it, > otherwise this is an empty/useless field that can never be touched again > in the future. > > Please spell it out in detail as to if you can ever use this later on, > and what the kernel will do (if anything) if it is set. > > And if "the kernel ignores it" then that means these bytes are now > "empty space never to be used again", right? Right, I will fix this in v5. ... > > > > + __u8 uuid[16]; > > > > > > You just changed the type here, so what is that going to break in > > > userspace that depended on this being of a structure type and now it's > > > an array? > > > > It's the same. The previous was hidden behind additional type level. > > Same size, yes. Same C structure definition, no. It doesn't matter, see below. > > > And no other kernel changes needed? Shouldn't you warn if this field is > > > set? > > > > No, as pointed out in the commit message kernel never ever used this. > > That does not mean that userspace tools never did, right? You are > changing the structure definition, what tool just broke? The only tool has been amended like a year ago, so the answer is none. The commit message has links to the commits in question that made that amendment. Maybe I should remove Fixes tags? In such case we will very much know that no old tools will be run on the new kernel. -- With Best Regards, Andy Shevchenko