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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 BCF2BC3402A for ; Mon, 17 Feb 2020 21:48:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9157F2070B for ; Mon, 17 Feb 2020 21:48:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="H+p1UwY0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729978AbgBQVsG (ORCPT ); Mon, 17 Feb 2020 16:48:06 -0500 Received: from mail-ed1-f65.google.com ([209.85.208.65]:39990 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728935AbgBQVsG (ORCPT ); Mon, 17 Feb 2020 16:48:06 -0500 Received: by mail-ed1-f65.google.com with SMTP id p3so22337064edx.7; Mon, 17 Feb 2020 13:48:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:reply-to:from:date:message-id :subject:to:cc; bh=zfMS77r2/yOT69zQZB5nUanXr9vmDwcibatswF77RLM=; b=H+p1UwY0pkxpP9j7tLcvoTxufeba8MCcndAMKeLxuH8IdIhOzeXQD8tOmiF/2a301y XAaXMFIBn/5LcPF5yJy/vmIXjQC2xtRIhXMm0E1n0jsVnKlLJIeVKDx6RXW13r4Q7H06 04bk9OYBeyEfXLOdoJGu3RLO6u0FMKYUmCXgPGy6aKMG7EdtuaHAIad+XVdBQg8xV+pp Q6kWvUmeX/MJZ0w6oka1GRbXw4LHE85qsrg9xJoc3Dx12eUdR5T65mlUyvuQqq1zlsVz 4c1eF5f3tgfF1yZTjyJ9wW3Nmkvy32hEr4avE7NQQa6ZN6iYoniXXs+AtE6wY/6hzsUQ kWRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:reply-to :from:date:message-id:subject:to:cc; bh=zfMS77r2/yOT69zQZB5nUanXr9vmDwcibatswF77RLM=; b=O1MSnS8CEILWujWies2U9UMN33s8xq547ar5cuk4CLEIUEX55sUhKSENcx4vdJ/nBu n5VRCw/yTYru4dbUzJmDcSfXPwPV5M01fEVgfnRgiXerK618JQUnb6I7cePMp1pBCTSE mCUvWcOIji0q2bbmWGPPgnHfYpmyA50ziDCPZ2xDVMGQwz9Q/T9WwxMD+rTqnR1G3CQY coEOUFqwyBkGCocNoGiDOwZjJOw3/G/EDVDccs80lYhFJARqD4V1cDlvU8Ilr2b+ZcPN LS/R1/AQ6AGyxd1YAxfFn6rg5jDdhmXlrcFYp3QBadHh3YmyD2NFav/Vy7OKKYXL2frI 718Q== X-Gm-Message-State: APjAAAXL4aZsOaUvXj5IhldGddJv5qSVYAkEyhG+Rodqix1MjBmBP+0a MG27MZEUqydDppqy5cR70l584Ubf4GBnkiFTUlk= X-Google-Smtp-Source: APXvYqwdswv+8mGQteeErSB7yFQjychp2XnULWOThIztPi9Y3g89o2LbrvtqVap9ZG9uYBcsUUGdgo7T4c9hhkrtsfQ= X-Received: by 2002:a17:906:7c9:: with SMTP id m9mr16348125ejc.243.1581976083916; Mon, 17 Feb 2020 13:48:03 -0800 (PST) MIME-Version: 1.0 References: <20191112012724.250792-1-dima@arista.com> <20191112012724.250792-4-dima@arista.com> <20200217145908.7epzz5nescccwvzv@wittgenstein> In-Reply-To: <20200217145908.7epzz5nescccwvzv@wittgenstein> Reply-To: mtk.manpages@gmail.com From: "Michael Kerrisk (man-pages)" Date: Mon, 17 Feb 2020 22:47:53 +0100 Message-ID: Subject: Re: Time Namespaces: CLONE_NEWTIME and clone3()? To: Christian Brauner Cc: Dmitry Safonov , Andrei Vagin , Linux Kernel , Dmitry Safonov <0x7f454c46@gmail.com>, Adrian Reber , Andy Lutomirski , Arnd Bergmann , Cyrill Gorcunov , "Eric W. Biederman" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Jeff Dike , Oleg Nesterov , Pavel Emelyanov , Shuah Khan , Thomas Gleixner , Vincenzo Frascino , containers , criu@openvz.org, Linux API , x86@kernel.org, Andrei Vagin Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Christian, On Mon, 17 Feb 2020 at 16:15, Christian Brauner wrote: > > On Mon, Feb 17, 2020 at 03:20:55PM +0100, Michael Kerrisk wrote: > > Hello Dmitry, Andrei, > > > > Is the CLONE_NEWTIME flag intended to be usable with clone3()? The > > mail quoted below implies (in my reading) that this should be possible > > once clone3() is available, which it is by now. (See also [1].) > > > > If the answer is yes, CLONE_NEWTIME should be usable with clone3(), > > then I have a bug report and a question. > > > > I successfully used CLONE_NEWTIME with unshare(). But if I try to use > > CLONE_NEWSIGNAL with clone3(), it errors out with EINVAL, because of > > s/CLONE_NEWSIGNAL/CLONE_NEWTIME/ > > > the following check in clone3_args_valid(): > > > > /* > > * - make the CLONE_DETACHED bit reuseable for clone3 > > * - make the CSIGNAL bits reuseable for clone3 > > */ > > if (kargs->flags & (CLONE_DETACHED | CSIGNAL)) > > return false; > > > > The problem is that CLONE_NEWTIME matches one of the bits in the > > CSIGNAL mask. If the intention is to allow CLONE_NEWTIME with > > clone3(), then either the bit needs to be redefined, or the error > > checking in clone3_args_valid() needs to be reworked. > > If this is intended to be useable with clone3() the check should be > adapted to allow for CLONE_NEWTIME. (I asked about this a while ago I > think.) > But below rather sounds like it should simply be an unshare() flag. The > code seems to set frozen_offsets to true right after copy_namespaces() > in timens_on_fork(new_ns, tsk) and so the offsets can't be changed > anymore unless I'm reading this wrong. > Alternatives seem to either make timens_offsets writable once after fork > and before exec, I guess - though that's probably not going to work > with the vdso judging from timens_on_fork(). > > The other alternative is that Andrei and Dmitry send me a patch to > enable CLONE_NEWTIME with clone3() by exposing struct timens_offsets (or > a version of it) in the uapi and extend struct clone_args to include a > pointer to a struct timens_offset that is _only_ set when CLONE_NEWTIME > is set. > Though the unshare() way sounds way less invasive simpler. Actually, I think the alternative you propose just here is better. I imagine there are times when one will want to create multiple namespaces with a single call to clone3(), including a time namespace. I think this should be allowed by the API. And, otherwise, clone3() becomes something of a second-class citizen for creating namespaces. (I don't really get the "less invasive" argument. Implementing this is just a piece of kernel to code to make user-space's life a bit simpler and more consistent.) Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/