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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 6B7E2C432C3 for ; Thu, 14 Nov 2019 00:59:06 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 70DB2206EC for ; Thu, 14 Nov 2019 00:59:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 70DB2206EC Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52576 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iV3TT-00057w-EM for qemu-devel@archiver.kernel.org; Wed, 13 Nov 2019 19:59:03 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:51175) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iV3Mn-0003EL-PL for qemu-devel@nongnu.org; Wed, 13 Nov 2019 19:52:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iV3Mi-0006xq-8Y for qemu-devel@nongnu.org; Wed, 13 Nov 2019 19:52:06 -0500 Received: from mga18.intel.com ([134.134.136.126]:7558) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iV3Mh-0006KL-UI for qemu-devel@nongnu.org; Wed, 13 Nov 2019 19:52:04 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 Nov 2019 16:51:55 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,302,1569308400"; d="scan'208";a="235481398" Received: from unknown (HELO [10.239.196.128]) ([10.239.196.128]) by fmsmga002.fm.intel.com with ESMTP; 13 Nov 2019 16:51:52 -0800 Subject: Re: [PATCH v14 03/11] tests: Add test for QAPI builtin type time To: Eduardo Habkost References: <20191028075220.25673-1-tao3.xu@intel.com> <20191028075220.25673-4-tao3.xu@intel.com> <20191106205359.GR3812@habkost.net> <1f2fa942-0993-548b-1f5c-8345d564bf29@intel.com> <20191107133112.GS3812@habkost.net> <9ecafb7f-69b9-870b-b109-939fef47acde@intel.com> <87lfsqbxnj.fsf@dusky.pond.sub.org> <20191112201558.GG3812@habkost.net> <8d8f7a45-b337-2ec8-d83d-4baec1efdaec@intel.com> <20191113220636.GK3812@habkost.net> From: Tao Xu Message-ID: Date: Thu, 14 Nov 2019 08:51:52 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20191113220636.GK3812@habkost.net> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 134.134.136.126 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "lvivier@redhat.com" , "thuth@redhat.com" , "mst@redhat.com" , "qemu-devel@nongnu.org" , "Liu, Jingqi" , "Du, Fan" , Markus Armbruster , "mdroth@linux.vnet.ibm.com" , "jonathan.cameron@huawei.com" , "imammedo@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/14/2019 6:06 AM, Eduardo Habkost wrote: > On Wed, Nov 13, 2019 at 09:01:29AM +0800, Tao Xu wrote: >> On 11/13/2019 4:15 AM, Eduardo Habkost wrote: >>> On Fri, Nov 08, 2019 at 09:05:52AM +0100, Markus Armbruster wrote: >>>> Tao Xu writes: >>>> >>>>> On 11/7/2019 9:31 PM, Eduardo Habkost wrote: >>>>>> On Thu, Nov 07, 2019 at 02:24:52PM +0800, Tao Xu wrote: >>>>>>> On 11/7/2019 4:53 AM, Eduardo Habkost wrote: >>>>>>>> On Mon, Oct 28, 2019 at 03:52:12PM +0800, Tao Xu wrote: >>>>>>>>> Add tests for time input such as zero, around limit of precision, >>>>>>>>> signed upper limit, actual upper limit, beyond limits, time suffixes, >>>>>>>>> and etc. >>>>>>>>> >>>>>>>>> Signed-off-by: Tao Xu >>>>>>>>> --- >>>>>>>> [...] >>>>>>>>> + /* Close to signed upper limit 0x7ffffffffffffc00 (53 msbs set) */ >>>>>>>>> + qdict = keyval_parse("time1=9223372036854774784," /* 7ffffffffffffc00 */ >>>>>>>>> + "time2=9223372036854775295", /* 7ffffffffffffdff */ >>>>>>>>> + NULL, &error_abort); >>>>>>>>> + v = qobject_input_visitor_new_keyval(QOBJECT(qdict)); >>>>>>>>> + qobject_unref(qdict); >>>>>>>>> + visit_start_struct(v, NULL, NULL, 0, &error_abort); >>>>>>>>> + visit_type_time(v, "time1", &time, &error_abort); >>>>>>>>> + g_assert_cmphex(time, ==, 0x7ffffffffffffc00); >>>>>>>>> + visit_type_time(v, "time2", &time, &error_abort); >>>>>>>>> + g_assert_cmphex(time, ==, 0x7ffffffffffffc00); >>>>>>>> >>>>>>>> I'm confused by this test case and the one below[1]. Are these >>>>>>>> known bugs? Shouldn't we document them as known bugs? >>>>>>> >>>>>>> Because do_strtosz() or do_strtomul() actually parse with strtod(), so the >>>>>>> precision is 53 bits, so in these cases, 7ffffffffffffdff and >>>>>>> fffffffffffffbff are rounded. >>>>>> >>>>>> My questions remain: why isn't this being treated like a bug? >>>>>> >>>>> Hi Markus, >>>>> >>>>> I am confused about the code here too. Because in do_strtosz(), the >>>>> upper limit is >>>>> >>>>> val * mul >= 0xfffffffffffffc00 >>>>> >>>>> So some data near 53 bit may be rounded. Is there a bug? >>>> >>>> No, but the design is surprising, and the functions lack written >>>> contracts, except for the do_strtosz() helper, which has one that sucks. >>>> >>>> qemu_strtosz() & friends are designed to accept fraction * unit >>>> multiplier. Example: 1.5M means 1.5 * 1024 * 1024 with qemu_strtosz() >>>> and qemu_strtosz_MiB(), and 1.5 * 1000 * 1000 with >>>> qemu_strtosz_metric(). Whether supporting fractions is a good idea is >>>> debatable, but it's what we've got. >>>> >>>> The implementation limits the numeric part to the precision of double, >>>> i.e. 53 bits. "8PiB should be enough for anybody." >>>> >>>> Switching it from double to long double raises the limit to the >>>> precision of long double. At least 64 bit on common hosts, but hosts >>>> exist where it's the same 53 bits. Do we support any such hosts? If >>>> yes, then we'd make the precision depend on the host, which feels like a >>>> bad idea. >>>> >>>> A possible alternative is to parse the numeric part both as a double and >>>> as a 64 bit unsigned integer, then use whatever consumes more >>>> characters. This enables providing full 64 bits unless you actually use >>>> a fraction. >>>> >>> >>> This sounds like the right thing to do, if user input is an >>> integer and the code in the other end is consuming an integer. >>> >>> >>>> As far as I remember, the only problem we've ever had with the 53 bits >>>> limit is developer confusion :) >>>> >>> >>> Developer confusion, I can deal with. However, exposing this >>> behavior on external interfaces is a bug to me. >>> >>> I don't know how serious the bug is because I don't know which >>> interfaces are affected by it. Do we have a list? >>> >>>> Patches welcome. >>> >>> My first goal is to get the maintainers of that code to recognize >>> it as a bug. Then I hope this will motivate somebody else to fix >>> it. :) >>> >> >> Hi Eduardo, >> >> If it is a bug, could the fix patch merged during rc1-rc3? Because I made 2 >> patches, and I want to submit before HMAT (HMAT patches is big, so submit >> together may be slow). > > Even if I convince other maintainers it is a bug, I don't think > it is serious enough to require a fix in QEMU 4.2. I suggest > finishing the ongoing HMAT work first, and worry about this issue > later. > > Or, if you really prefer to address it before HMAT, it's OK to > make the next version of the HMAT series depend on a series > that's not merged yet. Just make this explicit in the series > cover letter (publishing a git branch to help review and testing > is also appreciated). > OK I will submit them together.