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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 EDB33C00A89 for ; Fri, 30 Oct 2020 15:44:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 940CA20936 for ; Fri, 30 Oct 2020 15:44:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726899AbgJ3Po0 (ORCPT ); Fri, 30 Oct 2020 11:44:26 -0400 Received: from mail-out.m-online.net ([212.18.0.9]:39528 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726491AbgJ3Po0 (ORCPT ); Fri, 30 Oct 2020 11:44:26 -0400 Received: from frontend01.mail.m-online.net (unknown [192.168.8.182]) by mail-out.m-online.net (Postfix) with ESMTP id 4CN67B72Fjz1qs0P; Fri, 30 Oct 2020 16:44:22 +0100 (CET) Received: from localhost (dynscan1.mnet-online.de [192.168.6.70]) by mail.m-online.net (Postfix) with ESMTP id 4CN67B649sz1qv52; Fri, 30 Oct 2020 16:44:22 +0100 (CET) X-Virus-Scanned: amavisd-new at mnet-online.de Received: from mail.mnet-online.de ([192.168.8.182]) by localhost (dynscan1.mail.m-online.net [192.168.6.70]) (amavisd-new, port 10024) with ESMTP id ZGZQQ6uWxFJ6; Fri, 30 Oct 2020 16:44:21 +0100 (CET) X-Auth-Info: oCko4kOVV9bSFGSiWx9nh6Yq9889MkbD8f+dbL7NnSM= Received: from jawa (85-222-111-42.dynamic.chello.pl [85.222.111.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.mnet-online.de (Postfix) with ESMTPSA; Fri, 30 Oct 2020 16:44:21 +0100 (CET) Date: Fri, 30 Oct 2020 16:43:37 +0100 From: Lukasz Majewski To: Thomas Gleixner Cc: Andrei Vagin , Dmitry Safonov , GNU C Library , Arnd Bergmann , linux-kernel@vger.kernel.org Subject: Re: [Y2038][time namespaces] Question regarding CLOCK_REALTIME support plans in Linux time namespaces Message-ID: <20201030164337.347fe961@jawa> In-Reply-To: <871rhfoo7z.fsf@nanos.tec.linutronix.de> References: <20201030110229.43f0773b@jawa> <871rhfoo7z.fsf@nanos.tec.linutronix.de> Organization: denx.de X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; boundary="Sig_/_jqYRZN8T2/HbbtXNFCRlTS"; protocol="application/pgp-signature" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_/_jqYRZN8T2/HbbtXNFCRlTS Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Hi Thomas, > Lukasz, >=20 > On Fri, Oct 30 2020 at 11:02, Lukasz Majewski wrote: > > I do have a question regarding the Linux time namespaces in respect > > of adding support for virtualizing the CLOCK_REALTIME. > > > > According to patch description [1] and time_namespaces documentation > > [2] the CLOCK_REALTIME is not supported (for now?) to avoid > > complexity and overhead in the kernel. > > > > Is there any plan to add support for it in a near future? =20 >=20 > Not really. Just having an offset on clock realtime would be incorrect > in a number of ways. Doing it correct is a massive trainwreck. >=20 > For a debug aid, which is what you are looking for, the correctness > would not really matter, but providing that is a really slippery > slope. >=20 > If at all we could hide it under a debug option which depends on > CONFIG_BROKEN and emitting a big fat warning in dmesg with a clear > statement that it _is_ broken, stays so forever and any attempt to > "fix" it results in a permanent ban from all kernel lists. >=20 > Preferrably we don't go there. I see. Thanks for the explanation. Now, I do use QEMU to emulate ARM 32 bit system with recent kernel (5.1+). It works.=20 Another option would be to give a shoot to QEMU with the "user mode" to run cross-compiled tests (with using a cross-compiled glibc in earlier CI stage). The problem with above is the reliance on QEMU emulation of ARM syscalls (and if 64 bit time supporting syscalls - i.e. clock_settime64 - are available). >=20 > Thanks, >=20 > tglx >=20 >=20 Best regards, Lukasz Majewski -- DENX Software Engineering GmbH, Managing Director: Wolfgang Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de --Sig_/_jqYRZN8T2/HbbtXNFCRlTS Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEgAyFJ+N6uu6+XupJAR8vZIA0zr0FAl+cNKkACgkQAR8vZIA0 zr1kdQgAxMpyJHLr7oWeB34cpyPU5D+gz+HgLKq4LZS/Tf7xMe4aZuwmPAti5FCn Nxu9Mv3r5j/g33jV8ZD0GJih+/Bey+5HYk3veAnLsJ78j3mERFT6z77erMMqDC0T Yl1BxjbIpFWRm5342R1o6EUoGmxGFRkWESPr/GXpNdFJZDSHUcb+MRDrtykzQZic ImQbZ51jg51gRkdfWme+0fcx1+J4nX/9QnClW2vRFR6hKK21vtsPxfzS+x/jANyZ e/YpF8wSgVwQHFwaZikW3mlJQHJMkkyTBcETFsWlca+2IS0fTE4kAq3g7y+hUFAz I8scySUJAxMivKdyQkuSktPm2TyPQg== =YQGD -----END PGP SIGNATURE----- --Sig_/_jqYRZN8T2/HbbtXNFCRlTS--