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=-4.0 required=3.0 tests=BAYES_00, 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 3B211C433DF for ; Tue, 11 Aug 2020 19:50:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C0EF204EC for ; Tue, 11 Aug 2020 19:50:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726474AbgHKTuf (ORCPT ); Tue, 11 Aug 2020 15:50:35 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54056 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726173AbgHKTue (ORCPT ); Tue, 11 Aug 2020 15:50:34 -0400 Received: from ip5f5af08c.dynamic.kabel-deutschland.de ([95.90.240.140] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1k5aI2-0002GB-Ig; Tue, 11 Aug 2020 19:50:30 +0000 Date: Tue, 11 Aug 2020 21:50:29 +0200 From: Christian Brauner To: Lennart Poettering Cc: Miklos Szeredi , Linus Torvalds , linux-fsdevel , David Howells , Al Viro , Karel Zak , Jeff Layton , Miklos Szeredi , Nicolas Dichtel , Christian Brauner , Linux API , Ian Kent , LSM , Linux Kernel Mailing List Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information) Message-ID: <20200811195029.cnowfkikr2xajhgo@wittgenstein> References: <20200811135419.GA1263716@miu.piliscsaba.redhat.com> <20200811193105.GA228302@gardel-login> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200811193105.GA228302@gardel-login> Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Aug 11, 2020 at 09:31:05PM +0200, Lennart Poettering wrote: > On Di, 11.08.20 20:49, Miklos Szeredi (miklos@szeredi.hu) wrote: > > > On Tue, Aug 11, 2020 at 6:05 PM Linus Torvalds > > wrote: > > > > > and then people do "$(srctree)/". If you haven't seen that kind of > > > pattern where the pathname has two (or sometimes more!) slashes in the > > > middle, you've led a very sheltered life. > > > > Oh, I have. That's why I opted for triple slashes, since that should > > work most of the time even in those concatenated cases. And yes, I > > know, most is not always, and this might just be hiding bugs, etc... > > I think the pragmatic approach would be to try this and see how many > > triple slash hits a normal workload gets and if it's reasonably low, > > then hopefully that together with warnings for O_ALT would be enough. > > There's no point. Userspace relies on the current meaning of triple > slashes. It really does. > > I know many places in systemd where we might end up with a triple > slash. Here's a real-life example: some code wants to access the > cgroup attribute 'cgroup.controllers' of the root cgroup. It thus > generates the right path in the fs for it, which is the concatenation of > "/sys/fs/cgroup/" (because that's where cgroupfs is mounted), of "/" > (i.e. for the root cgroup) and of "/cgroup.controllers" (as that's the > file the attribute is exposed under). > > And there you go: > > "/sys/fs/cgroup/" + "/" + "/cgroup.controllers" → "/sys/fs/cgroup///cgroup.controllers" > > This is a real-life thing. Don't break this please. Taken from a log from a container: lxc f4 20200810105815.742 TRACE cgfsng - cgroups/cgfsng.c:cg_legacy_handle_cpuset_hierarchy:552 - "cgroup.clone_children" was already set to "1" lxc f4 20200810105815.742 WARN cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset///lxc.monitor.f4" lxc f4 20200810105815.743 INFO cgfsng - cgroups/cgfsng.c:cgfsng_monitor_create:1366 - The monitor process uses "lxc.monitor.f4" as cgroup lxc f4 20200810105815.743 DEBUG storage - storage/storage.c:get_storage_by_name:211 - Detected rootfs type "dir" lxc f4 20200810105815.743 TRACE cgfsng - cgroups/cgfsng.c:cg_legacy_handle_cpuset_hierarchy:552 - "cgroup.clone_children" was already set to "1" lxc f4 20200810105815.743 WARN cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset///lxc.payload.f4" lxc f4 20200810105815.743 INFO cgfsng - cgroups/cgfsng.c:cgfsng_payload_create:1469 - The container process uses "lxc.payload.f4" as cgroup lxc f4 20200810105815.744 TRACE start - start.c:lxc_spawn:1731 - Spawned container directly into target cgroup via cgroup2 fd 17 Christian