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[209.132.180.67]) by mx.google.com with ESMTP id a185si9318373oii.252.2020.03.24.10.57.39; Tue, 24 Mar 2020 10:57:53 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727561AbgCXR5I (ORCPT + 99 others); Tue, 24 Mar 2020 13:57:08 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:51828 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727466AbgCXR5I (ORCPT ); Tue, 24 Mar 2020 13:57:08 -0400 Received: from ip5f5bf7ec.dynamic.kabel-deutschland.de ([95.91.247.236] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1jGnnH-0005ms-Ii; Tue, 24 Mar 2020 17:56:51 +0000 Date: Tue, 24 Mar 2020 18:56:49 +0100 From: Christian Brauner To: Adrian Reber Cc: Andrei Vagin , Arnd Bergmann , Eric Biederman , Pavel Emelyanov , Oleg Nesterov , Dmitry Safonov <0x7f454c46@gmail.com>, "linux-kernel@vger.kernel.org" , Mike Rapoport , Radostin Stoyanov , Michael Kerrisk , Cyrill Gorcunov , Thomas Gleixner , Aleksa Sarai , Linux API Subject: Re: clone3: allow creation of time namespace with offset Message-ID: <20200324175649.fqkwiuvs2drk26ln@wittgenstein> References: <20200317083043.226593-1-areber@redhat.com> <20200319081137.GC223854@dcbz.redhat.com> <20200319102955.i7slokibkkysz6g6@wittgenstein> <20200320183355.GA118769@gmail.com> <20200324160945.orcm75avj2ol3eop@wittgenstein> <20200324162546.GG358599@dcbz.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200324162546.GG358599@dcbz.redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 24, 2020 at 05:25:46PM +0100, Adrian Reber wrote: > On Tue, Mar 24, 2020 at 05:09:45PM +0100, Christian Brauner wrote: > > On Fri, Mar 20, 2020 at 11:33:55AM -0700, Andrei Vagin wrote: > > > On Thu, Mar 19, 2020 at 11:29:55AM +0100, Christian Brauner wrote: > > > > On Thu, Mar 19, 2020 at 09:16:43AM +0100, Arnd Bergmann wrote: > > > > > On Thu, Mar 19, 2020 at 9:11 AM Adrian Reber wrote: > > > > > > > > > > > With Arnd's idea of only using nanoseconds, timens_offset would then > > > > > > contain something like this: > > > > > > > > > > > > struct timens_offset { > > > > > > __aligned_s64 monotonic_offset_ns; > > > > > > __aligned_s64 boottime_offset_ns; > > > > > > }; > > > > > > > > > > > > I kind of prefer adding boottime and monotonic directly to struct clone_args > > > > > > > > > > > > __aligned_u64 tls; > > > > > > __aligned_u64 set_tid; > > > > > > __aligned_u64 set_tid_size; > > > > > > + __aligned_s64 monotonic_offset_ns; > > > > > > + __aligned_s64 boottime_offset_ns; > > > > > > }; > > > > > > > > > > I would also prefer the second approach using two 64-bit integers > > > > > instead of a pointer, as it keeps the interface simpler to implement > > > > > and simpler to interpret by other tools. > > > > > > > > Why I don't like has two reasons. There's the scenario where we have > > > > added new extensions after the new boottime member and then we introduce > > > > another offset. Then you'd be looking at: > > > > > > > > __aligned_u64 tls; > > > > __aligned_u64 set_tid; > > > > __aligned_u64 set_tid_size; > > > > + __aligned_s64 monotonic_offset_ns; > > > > + __aligned_s64 boottime_offset_ns; > > > > __aligned_s64 something_1 > > > > __aligned_s64 anything_2 > > > > + __aligned_s64 sometime_offset_ns > > > > > > > > which bothers me just by looking at it. That's in addition to adding two > > > > new members to the struct when most people will never set CLONE_NEWTIME. > > > > We'll also likely have more features in the future that will want to > > > > pass down more info than we want to directly expose in struct > > > > clone_args, e.g. for a long time I have been thinking about adding a > > > > struct for CLONE_NEWUSER that allows you to specify the id mappings you > > > > want the new user namespace to get. We surely don't want to force all > > > > new info into the uppermost struct. So I'm not convinced we should here. > > > > > > I think here we can start thinking about a netlink-like interface. > > > > I think netlink is just not a great model for an API and I would not > > want us to go down that route. > > > > I kept thinking about this for a bit and I think that we will end up > > growing more namespace-related functionality. So one thing that came to > > my mind is the following layout: > > > > struct { > > struct { > > __s64 monotonic; > > __s64 boot; > > } time; > > } namespaces; > > > > struct _clone_args { > > __aligned_u64 flags; > > __aligned_u64 pidfd; > > __aligned_u64 child_tid; > > __aligned_u64 parent_tid; > > __aligned_u64 exit_signal; > > __aligned_u64 stack; > > __aligned_u64 stack_size; > > __aligned_u64 tls; > > __aligned_u64 set_tid; > > __aligned_u64 set_tid_size; > > __aligned_u64 namespaces; > > __aligned_u64 namespaces_size; > > }; > > > > Then when we end up adding id mapping support for CLONE_NEWUSER we can > > extend this with: > > > > struct { > > struct { > > __aligned_u64 monotonic; > > __aligned_u64 boot; s/__aligned_u64/__s64/g Sorry, leftover from my first draft. > > } time; > > > > struct { > > /* id mapping members */ > > } user; > > } namespaces; > > > > Thoughts? Other ideas? > > Works for me. > > If we add the user namespace id mappings and then at some point a third > element for the time namespace appears it would also start to be mixed. > Just as you mentioned that a few mails ago. I think you misunderstand me or I'm misunderstanding you. That new time namespace member would go into struct time {} so struct { struct { __s64 monotonic; __s64 boot; __s64 someothertime; } time; struct { /* id mapping members */ } user; } namespaces; Christian