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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 A8290C43603 for ; Fri, 6 Dec 2019 16:13:43 +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 7330E206DF for ; Fri, 6 Dec 2019 16:13:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="UlMiMOXj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7330E206DF 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]:40544 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idGEg-0007To-Fs for qemu-devel@archiver.kernel.org; Fri, 06 Dec 2019 11:13:42 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:48657) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1idF8l-0003SR-Vs for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:03:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1idF8k-0000of-7y for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:03:31 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:47915 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1idF8k-0000na-3P for qemu-devel@nongnu.org; Fri, 06 Dec 2019 10:03:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1575644609; 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=CCYAJx/IIBCLtbXTluUDn5tA+V9Tc3YwcHu39RSQD3E=; b=UlMiMOXj7gsPlcx1yD5Ym/GuSl533jlRvreCTaAengSmyfxDlfPK0KgbuG0ur6DPoipwwk rn7ohLSKM70w3CuU/kmQgyNDJX4hb4aDHLB3d785EgXlbg8P3FKBhUT2sh7O8irp8pY4+E dMzrLLBmgIOeZbczf6+9wSKQrcBDmNM= 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-432-QtOnezTVMeCNVSJiBR7SoQ-1; Fri, 06 Dec 2019 04:02:40 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C9D501005512; Fri, 6 Dec 2019 09:02:39 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-116-235.ams2.redhat.com [10.36.116.235]) by smtp.corp.redhat.com (Postfix) with ESMTP id B84E65D6BB; Fri, 6 Dec 2019 09:02:35 +0000 (UTC) Subject: Re: [PATCH v3] qga: fence guest-set-time if hwclock not available To: Markus Armbruster References: <20191205115350.18713-1-cohuck@redhat.com> <5aaa7f3a-e3d1-0057-5fe2-07dea4864bc7@redhat.com> <87h82dorfn.fsf@dusky.pond.sub.org> From: Laszlo Ersek Message-ID: Date: Fri, 6 Dec 2019 10:02:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <87h82dorfn.fsf@dusky.pond.sub.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: QtOnezTVMeCNVSJiBR7SoQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: "=?UTF-8?Q?Daniel_P_._Berrang=c3=a9?=" , Cornelia Huck , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Michael Roth , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 12/06/19 08:15, Markus Armbruster wrote: > Laszlo Ersek writes: >=20 >> On 12/05/19 14:05, Philippe Mathieu-Daud=C3=A9 wrote: >>> Hi Cornelia, >>> >>> On 12/5/19 12:53 PM, Cornelia Huck wrote: >>>> The Posix implementation of guest-set-time invokes hwclock to >>>> set/retrieve the time to/from the hardware clock. If hwclock >>>> is not available, the user is currently informed that "hwclock >>>> failed to set hardware clock to system time", which is quite >>>> misleading. This may happen e.g. on s390x, which has a different >>>> timekeeping concept anyway. >>>> >>>> Let's check for the availability of the hwclock command and >>>> return QERR_UNSUPPORTED for guest-set-time if it is not available. >>>> >>>> Reviewed-by: Laszlo Ersek >>>> Reviewed-by: Daniel P. Berrang=C3=A9 >>>> Reviewed-by: Michael Roth >>>> Signed-off-by: Cornelia Huck >>>> --- >>>> >>>> v2->v3: >>>> - added 'static' keyword to hwclock_path >>>> >>>> Not sure what tree this is going through; if there's no better place, >>>> I can also take this through the s390 tree. >>> >>> s390 or trivial trees seems appropriate. >>> >>>> >>>> --- >>>> qga/commands-posix.c | 13 ++++++++++++- >>>> 1 file changed, 12 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c >>>> index 1c1a165daed8..0be301a4ea77 100644 >>>> --- a/qga/commands-posix.c >>>> +++ b/qga/commands-posix.c >>>> @@ -156,6 +156,17 @@ void qmp_guest_set_time(bool has_time, int64_t >>>> time_ns, Error **errp) >>>> pid_t pid; >>>> Error *local_err =3D NULL; >>>> struct timeval tv; >>>> + static const char hwclock_path[] =3D "/sbin/hwclock"; >>>> + static int hwclock_available =3D -1; >>>> + >>>> + if (hwclock_available < 0) { >>>> + hwclock_available =3D (access(hwclock_path, X_OK) =3D=3D 0); >>>> + } >>>> + >>>> + if (!hwclock_available) { >>>> + error_setg(errp, QERR_UNSUPPORTED); >>> >>> In include/qapi/qmp/qerror.h we have: >>> >>> /* >>> * These macros will go away, please don't use in new code, and do not >>> * add new ones! >>> */ >> >> Obviously, the last word on this belongs to Markus (CC'd) -- he added >> that comment. I'd just like to point out *when* that comment was added: >> approx. four and half years ago. (See commit 4629ed1e9896.) >=20 > Yes, with a big push to finally kill qerror_report(). I was too > exhausted to finish the job and kill all the remaining QERR_, too. >=20 > I'm dead serious on the "do not add new ones" part. >=20 > On the "don't use in new code" part, I'm quite willing to tolerate > reasonable exceptions, e.g. to maintain consistency with old code. >=20 > This one looks like a reasonable exception to me. >=20 >> I've always associated QERR_UNSUPPORTED with QMP interfaces rejecting >> invocation due to lack of support. I don't think one more instance of >> QERR_UNSUPPORTED will matter much, when we'll "finally" :) convert or >> eliminate the other 35! (Yes, I've counted.) >> >> In case it's unacceptable to add one more QERR_UNSUPPORTED: what is the >> official solution that replaces it? >> >> I assume it was explained in the series that included commit >> 4629ed1e9896, but I can't easily tell. (And, there is no "QERR_" match >> in docs/.) >=20 > See "exhausted" above. >=20 >> Hmmm, more history digging... In the 4629ed1e9896..v4.2.0-rc4 set of >> commits, the following commits introduced new instances of >> QERR_UNSUPPORTED: >> >> - e09484efbc9d ("qmp: add QMP interface "query-cpu-model-expansion"", 20= 16-09-06) >> - 0031e0d68339 ("qmp: add QMP interface "query-cpu-model-comparison"", 2= 016-09-06) >> - b18b6043341d ("qmp: add QMP interface "query-cpu-model-baseline"", 201= 6-09-06) >> - 1007a37e2082 ("smbios: filter based on CONFIG_SMBIOS rather than TARGE= T", 2017-01-16) >> - 9f57061c3555 ("acpi: filter based on CONFIG_ACPI_X86 rather than TARGE= T", 2017-01-16) >> - 39164c136cba ("qmp/hmp: add query-vm-generation-id and 'info vm-genera= tion-id' commands", 2017-03-02) >> - 161a56a9065f ("qga: Add 'guest-get-users' command", 2017-04-26) >> - 53c58e64d0a2 ("qga: Add `guest-get-timezone` command", 2017-04-27) >> - e674605f9821 ("qemu-ga: check if utmpx.h is available on the system", = 2017-07-17) >> >> I don't claim that all of those additions have stuck with us, to >> v4.2.0-rc4. Yet, in general, practice doesn't seem to have followed the >> intended deprecation. >> >>> >>> Maybe we can replace it by "this feature is not supported on this >>> architecture"? (or without 'on this architecture'). >> >> I think if we replace QERR_UNSUPPORTED with anything, it should be >> "similarly standardized". (Lack of support for a given QMP interface is >> pretty common, I think.) >=20 > Here's my the general idea on getting rid of qerror.h. The QERR_ macros > effectively factor out common error message format strings. DRY is a > legitimate concern. However, I dislike (1) passing anything but string > literals as format to printf()-style function, and (2) tempting people > to reuse existing error messages where a new error message would be more > helpful. >=20 > Note that the error_setg() is *also* common. So take DRY to the next > level: factor out the common error_setg(errp, "literal error format > string", ...) along with whatever error handling is also common in a > helper function, and call that. Good point, I didn't think of (e.g.) error_set_qmp_unsupported(). Thank you for the details! Laszlo >=20 > However, do that only where the errors are truly common. Where they're > just similar, duplicate the error message, and maybe specialize it for > specific error situations. >=20 >>>> + return; >>>> + } >>>> /* If user has passed a time, validate and set it. */ >>>> if (has_time) { >>>> @@ -195,7 +206,7 @@ void qmp_guest_set_time(bool has_time, int64_t >>>> time_ns, Error **errp) >>>> /* Use '/sbin/hwclock -w' to set RTC from the system time, >>>> * or '/sbin/hwclock -s' to set the system time from RTC. */ >>>> - execle("/sbin/hwclock", "hwclock", has_time ? "-w" : "-s", >>>> + execle(hwclock_path, "hwclock", has_time ? "-w" : "-s", >>>> NULL, environ); >>>> _exit(EXIT_FAILURE); >>>> } else if (pid < 0) { >>>> >>>