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=-17.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 5CB5BC433E0 for ; Thu, 4 Feb 2021 20:13:52 +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 AC89B64F67 for ; Thu, 4 Feb 2021 20:13:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AC89B64F67 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]:38968 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7l0b-0000Nk-2O for qemu-devel@archiver.kernel.org; Thu, 04 Feb 2021 15:13:45 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:35634) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7kzj-0008Ij-BA for qemu-devel@nongnu.org; Thu, 04 Feb 2021 15:12:51 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:31033) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7kzf-0003Yl-6Z for qemu-devel@nongnu.org; Thu, 04 Feb 2021 15:12:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612469564; 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=YfophCiIB9zra3Y5ymTvwCo1KMyI9S8r5R47FgHiHBU=; b=YAZH04bKpO7uD5q2YLalOF/YZ4hB8O2BDSPhSnBeAzz9NRJQdDm2U3NydmfhIKB13RbUoV 4W06VDrpZ2FH/bU2rhT4ZSxMY/8PaSSMBGbuXzN13D/CdSAkf2NwWvkQpwZ9Ha+6ai8dVn zOAFdTxyT+PbEmME/EycTUc6bgjG8Yg= 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-247-wDnOQNyCPxuKNg1higrhnA-1; Thu, 04 Feb 2021 15:12:42 -0500 X-MC-Unique: wDnOQNyCPxuKNg1higrhnA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5C33885B664; Thu, 4 Feb 2021 20:12:41 +0000 (UTC) Received: from [10.3.112.103] (ovpn-112-103.phx2.redhat.com [10.3.112.103]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 862DF10074FC; Thu, 4 Feb 2021 20:12:40 +0000 (UTC) From: Eric Blake To: qemu-devel@nongnu.org References: <20210204190708.1306296-1-eblake@redhat.com> <20210204190708.1306296-2-eblake@redhat.com> Organization: Red Hat, Inc. Subject: Re: [PATCH 1/3] utils: Improve qemu_strtosz() to have 64 bits of precision Message-ID: Date: Thu, 4 Feb 2021 14:12:39 -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: <20210204190708.1306296-2-eblake@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, 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: , Cc: Kevin Wolf , vsementsov@virtuozzo.com, berrange@redhat.com, qemu-block@nongnu.org, tao3.xu@intel.com, armbru@redhat.com, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/4/21 1:07 PM, 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 > 2^64, so we have to explicitly check whether the user passed in a '-'. > > 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 inadvertenly accepted before). inadvertently > > Signed-off-by: Eric Blake > > --- > Is it a bad sign when I review my own code? > > /* > - * Convert string to bytes, allowing either B/b for bytes, K/k for KB, > - * M/m for MB, G/g for GB or T/t for TB. End pointer will be returned > - * in *end, if not NULL. Return -ERANGE on overflow, and -EINVAL on > - * other error. > + * Convert size string to bytes. > + * > + * Allow either B/b for bytes, K/k for KB, M/m for MB, G/g for GB or > + * T/t for TB, with scaling based on @unit, and with @default_suffix > + * implied if no explicit suffix was given. Reformatted existing text, but incomplete; we also support 'P' and 'E'. > + * > + * The end pointer will be returned in *end, if not NULL. If there is > + * no fraction, the input can be decimal or hexadecimal; if there is a > + * fraction, then the input must be decimal and there must be a suffix > + * (possibly by @default_suffix) larger than Byte, and the fractional > + * portion may suffer from precision loss or rounding. The input must > + * be positive. > + * > + * Return -ERANGE on overflow (with *@end advanced), and -EINVAL on > + * other error (with *@end left unchanged). If we take patch 2 and 3, this contract should also be updated to mention what we consider to be deprecated. > */ > static int do_strtosz(const char *nptr, const char **end, > const char default_suffix, int64_t unit, > @@ -253,40 +264,66 @@ static int do_strtosz(const char *nptr, const char **end, > int retval; > const char *endptr; > unsigned char c; > - int mul_required = 0; > - double val, mul, integral, fraction; > + bool mul_required = false; > + uint64_t val; > + int64_t mul; > + double fraction = 0.0; > > - retval = qemu_strtod_finite(nptr, &endptr, &val); > + /* Parse integral portion as decimal. */ > + retval = qemu_strtou64(nptr, &endptr, 10, &val); > if (retval) { > goto out; > } > - fraction = modf(val, &integral); > - if (fraction != 0) { > - mul_required = 1; > + if (strchr(nptr, '-') != NULL) { > + retval = -ERANGE; > + goto out; > + } > + if (val == 0 && (*endptr == 'x' || *endptr == 'X')) { > + /* Input looks like hex, reparse, and insist on no fraction. */ > + retval = qemu_strtou64(nptr, &endptr, 16, &val); > + if (retval) { > + goto out; > + } > + if (*endptr == '.') { > + endptr = nptr; > + retval = -EINVAL; > + goto out; > + } > + } else if (*endptr == '.') { > + /* Input is fractional, insist on 0 <= fraction < 1, with no exponent */ > + retval = qemu_strtod_finite(endptr, &endptr, &fraction); > + if (retval) { > + endptr = nptr; > + goto out; > + } > + if (fraction >= 1.0 || memchr(nptr, 'e', endptr - nptr) > + || memchr(nptr, 'E', endptr - nptr)) { > + endptr = nptr; > + retval = -EINVAL; > + goto out; > + } > + if (fraction != 0) { > + mul_required = true; > + } > } > c = *endptr; > mul = suffix_mul(c, unit); > - if (mul >= 0) { > + if (mul > 0) { > endptr++; > } else { > mul = suffix_mul(default_suffix, unit); > - assert(mul >= 0); > + assert(mul > 0); > } > if (mul == 1 && mul_required) { > + endptr = nptr; > retval = -EINVAL; > goto out; > } > - /* > - * Values near UINT64_MAX overflow to 2**64 when converting to double > - * precision. Compare against the maximum representable double precision > - * value below 2**64, computed as "the next value after 2**64 (0x1p64) in > - * the direction of 0". > - */ > - if ((val * mul > nextafter(0x1p64, 0)) || val < 0) { > + if (val > UINT64_MAX / mul) { Hmm, do we care about: 15.9999999999999999999999999999E where the fractional portion becomes large enough to actually bump our sum below to 16E which indeed overflows? Then again, we rejected a fraction of 1.0 above, and 0.9999999999999999999999999999 parses to 1.0 due to rounding. Maybe it's just worth a good comment why the overflow check here works without consulting fraction. > retval = -ERANGE; > goto out; > } > - *result = val * mul; > + *result = val * mul + (uint64_t) (fraction * mul); > retval = 0; > > out: -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org