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=-5.4 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 3A722C433DB for ; Fri, 5 Feb 2021 14:16:56 +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 3F49265021 for ; Fri, 5 Feb 2021 14:16:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3F49265021 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:51456 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l81un-00044V-Tz for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 09:16:53 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36052) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l81ti-0003UY-EF for qemu-devel@nongnu.org; Fri, 05 Feb 2021 09:15:46 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:24535) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l81tQ-0006On-QO for qemu-devel@nongnu.org; Fri, 05 Feb 2021 09:15:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612534528; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ljw2wLhpi9oYkBLh7xIF1ZgGHNv8l9odOL91z775Gio=; b=i4VOzPDoomZyv/yYtXWhswzLQzDBma5Wpgk+3jlmvsdDmTer8kjDpTtynEF/5j32aXJ/eS 3XHrF8EaJW02X1qlzupsHG1HarwCZEiAKDk16yn7tJ5XBxGbCJ6u5kDS6jOBrY/x+ICdfV oOwEkab1svZ/ftk61Mjr0QYUX2lB6bs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-350-X4B9pbt9MxK7XYGTKbmEJQ-1; Fri, 05 Feb 2021 09:15:26 -0500 X-MC-Unique: X4B9pbt9MxK7XYGTKbmEJQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2A6F0192AB7A; Fri, 5 Feb 2021 14:15:25 +0000 (UTC) Received: from [10.3.112.253] (ovpn-112-253.phx2.redhat.com [10.3.112.253]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 517A65DEF9; Fri, 5 Feb 2021 14:15:24 +0000 (UTC) Subject: Re: [PATCH 1/3] utils: Improve qemu_strtosz() to have 64 bits of precision To: "Richard W.M. Jones" References: <20210204190708.1306296-1-eblake@redhat.com> <20210204190708.1306296-2-eblake@redhat.com> <20210205102805.GA30079@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <03923751-7a8e-2e64-6eab-b49c604d4590@redhat.com> Date: Fri, 5 Feb 2021 08:15:23 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <20210205102805.GA30079@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eblake@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.352, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.33, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Kevin Wolf , vsementsov@virtuozzo.com, berrange@redhat.com, qemu-block@nongnu.org, tao3.xu@intel.com, qemu-devel@nongnu.org, armbru@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/5/21 4:28 AM, Richard W.M. Jones wrote: > On Thu, Feb 04, 2021 at 01:07:06PM -0600, Eric Blake wrote: >> We have multiple clients of qemu_strtosz (qemu-io, the opts visitor, >> the keyval visitor), and it gets annoying that edge-case testing is >> impacted by implicit rounding to 53 bits of precision due to parsing >> with strtod(). As an example posted by Rich Jones: >> $ nbdkit memory $(( 2**63 - 2**30 )) --run \ >> 'build/qemu-io -f raw "$uri" -c "w -P 3 $(( 2**63 - 2**30 - 512 )) 512" ' >> write failed: Input/output error >> >> because 9223372035781033472 got rounded to 0x7fffffffc0000000 which is >> out of bounds. >> >> It is also worth noting that our existing parser, by virtue of using >> strtod(), accepts decimal AND hex numbers, even though test-cutils >> previously lacked any coverage of the latter. We do have existing >> clients that expect a hex parse to work (for example, iotest 33 using >> qemu-io -c "write -P 0xa 0x200 0x400"), but strtod() parses "08" as 8 >> rather than as an invalid octal number, so we know there are no >> clients that depend on octal. Our use of strtod() also means that >> "0x1.8k" would actually parse as 1536 (the fraction is 8/16), rather >> than 1843 (if the fraction were 8/10); but as this was not covered in >> the testsuite, I have no qualms forbidding hex fractions as invalid, >> so this patch declares that the use of fractions is only supported >> with decimal input, and enhances the testsuite to document that. >> >> Our previous use of strtod() meant that -1 parsed as a negative; now >> that we parse with strtoull(), negative values can wrap around module > > ^^ modulo > > The patch looked fine to me although Vladimir found some problems > which I didn't spot. I have a question: What happens with leading or > trailing whitespace? Is that ignored, rejected or impossible? leading whitespace: ignored (because both strtod() pre-patch, and now strtoull() post-patch, do so for free). And that is why we have to memchr() (and not strchr(), as pointed out by Vladimir) for a '-' sign, because merely checking *nptr=='-' would be wrong in the presence of leading space. trailing whitespace: treated the same as any other trailing garbage (again, what strtod() and strtoull() give you for free). If endptr was non-NULL, then *endptr now points to that trailing space; if it was NULL, the parse is rejected because of the trailing garbage. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org