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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:53220 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lEbGH-0004UI-5O for qemu-devel@archiver.kernel.org; Tue, 23 Feb 2021 12:14:13 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48908) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lEbFO-0003xl-Lx for qemu-devel@nongnu.org; Tue, 23 Feb 2021 12:13:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41759) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lEbFM-0000yR-6h for qemu-devel@nongnu.org; Tue, 23 Feb 2021 12:13:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614100394; h=from:from:reply-to: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=DcgydohWU8EZ5dNqkvW5WRZ4AOS74VMFKVy431vWr90=; b=VV+YS75IWLrWO9XwQpReBaof1SmZM+G4flrjQRzrpAUcNa4dDMz4aFQURQri/WkV/uDQY5 SArVy6ib9nNY6BNiwoP78vXHN9jf6hjmNFdcCajyFtyNSy3BtAQZEbFpvLzA4BGM1fJxcY U6vtw/5gHOM/19EyGGZVN2JheTG4UuM= 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-563-mT4UfS9AO2m3Lt0hPMC_SQ-1; Tue, 23 Feb 2021 12:13:07 -0500 X-MC-Unique: mT4UfS9AO2m3Lt0hPMC_SQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9BF9818E8761; Tue, 23 Feb 2021 17:13:06 +0000 (UTC) Received: from redhat.com (ovpn-115-33.ams2.redhat.com [10.36.115.33]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 63B8B5C3FD; Tue, 23 Feb 2021 17:13:04 +0000 (UTC) Date: Tue, 23 Feb 2021 17:13:01 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Subject: Re: [PATCH v2 2/4] utils: Improve qemu_strtosz() to have 64 bits of precision Message-ID: References: <20210211204438.1184395-1-eblake@redhat.com> <20210211204438.1184395-3-eblake@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210211204438.1184395-3-eblake@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , vsementsov@virtuozzo.com, qemu-block@nongnu.org, rjones@redhat.com, tao3.xu@intel.com, armbru@redhat.com, qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Feb 11, 2021 at 02:44:36PM -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 until the previous patch. > 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 modulo > 2^64, so we have to explicitly check whether the user passed in a '-'; > and make it consistent to also reject '-0'. This has the minor effect > of treating negative values as EINVAL (with no change to endptr) > rather than ERANGE (with endptr advanced to what was parsed), visible > in the updated iotest output. > > We also had no testsuite coverage of "1.1e0k", which happened to parse > under strtod() but is unlikely to occur in practice; as long as we are > making things more robust, it is easy enough to reject the use of > exponents in a strtod parse. > > The fix is done by breaking the parse into an integer prefix (no loss > in precision), rejecting negative values (since we can no longer rely > on strtod() to do that), determining if a decimal or hexadecimal parse > was intended (with the new restriction that a fractional hex parse is > not allowed), and where appropriate, using a floating point fractional > parse (where we also scan to reject use of exponents in the fraction). > The bulk of the patch is then updates to the testsuite to match our > new precision, as well as adding new cases we reject (whether they > were rejected or inadvertently accepted before). > > Signed-off-by: Eric Blake > > --- > > Note that this approach differs from what has been attempted in the > past; see the thread starting at > https://lists.gnu.org/archive/html/qemu-devel/2019-12/msg00852.html > That approach tried to parse both as strtoull and strtod and take > whichever was longer, but that was harder to document. > --- > tests/test-cutils.c | 74 ++++++++++---------------- > tests/test-keyval.c | 35 +++++++++---- > tests/test-qemu-opts.c | 33 ++++++++---- > util/cutils.c | 90 ++++++++++++++++++++++++-------- > tests/qemu-iotests/049.out | 14 +++-- > tests/qemu-iotests/178.out.qcow2 | 3 +- > tests/qemu-iotests/178.out.raw | 3 +- > 7 files changed, 158 insertions(+), 94 deletions(-) Reviewed-by: Daniel P. Berrangé Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|