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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Lennart Poettering <mzxreary@0pointer.de>
Cc: Miklos Szeredi <miklos@szeredi.hu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	David Howells <dhowells@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>, Karel Zak <kzak@redhat.com>,
	Jeff Layton <jlayton@redhat.com>,
	Miklos Szeredi <mszeredi@redhat.com>,
	Nicolas Dichtel <nicolas.dichtel@6wind.com>,
	Christian Brauner <christian@brauner.io>,
	Linux API <linux-api@vger.kernel.org>,
	Ian Kent <raven@themaw.net>,
	LSM <linux-security-module@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)
Date: Tue, 11 Aug 2020 21:50:29 +0200	[thread overview]
Message-ID: <20200811195029.cnowfkikr2xajhgo@wittgenstein> (raw)
In-Reply-To: <20200811193105.GA228302@gardel-login>

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
> > <torvalds@linux-foundation.org> 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

  reply	other threads:[~2020-08-11 19:50 UTC|newest]

Thread overview: 89+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 15:27 [GIT PULL] Mount notifications David Howells
2020-08-03 15:49 ` [GIT PULL] Filesystem Information David Howells
2020-08-03 16:42   ` Miklos Szeredi
2020-08-04  2:15     ` Ian Kent
2020-08-04 14:36       ` Miklos Szeredi
2020-08-05  1:33         ` Ian Kent
2020-08-05  8:00           ` Miklos Szeredi
2020-08-05 11:13             ` Ian Kent
2020-08-05  8:24         ` file metadata via fs API (was: [GIT PULL] Filesystem Information) Miklos Szeredi
2020-08-11 13:54           ` Miklos Szeredi
2020-08-11 14:08             ` Al Viro
2020-08-11 14:22               ` Miklos Szeredi
2020-08-11 14:31                 ` Al Viro
     [not found]                   ` <CAAgocE07=vVKpQhG+rjEGO=NEBKZ02gjg4TRPxECAc+RKrzn=Q@mail.gmail.com>
2020-08-11 14:36                     ` Al Viro
2020-08-11 14:36                   ` Miklos Szeredi
2020-08-11 14:42                     ` Al Viro
2020-08-11 14:47                       ` Miklos Szeredi
2020-08-11 15:20             ` Linus Torvalds
2020-08-11 15:30               ` Miklos Szeredi
2020-08-11 16:05                 ` Linus Torvalds
2020-08-11 18:49                   ` Miklos Szeredi
2020-08-11 19:31                     ` Lennart Poettering
2020-08-11 19:50                       ` Christian Brauner [this message]
2020-08-11 19:39                   ` Christian Brauner
2020-08-12  0:53                     ` Ian Kent
2020-08-11 15:39               ` Andy Lutomirski
2020-08-11 16:17                 ` Casey Schaufler
2020-08-11 16:30                   ` Linus Torvalds
2020-08-11 20:28                   ` Miklos Szeredi
2020-08-11 20:36                     ` Jann Horn
2020-08-11 20:56                       ` Miklos Szeredi
2020-08-11 21:17                         ` Andy Lutomirski
2020-08-11 21:18                         ` Linus Torvalds
2020-08-12  7:23                           ` Miklos Szeredi
2020-08-12 14:39                             ` Al Viro
2020-08-12 14:46                               ` Miklos Szeredi
2020-08-12 15:08                                 ` Al Viro
2020-08-12 15:13                                   ` Miklos Szeredi
2020-08-12 16:33                                     ` Al Viro
2020-08-12 17:16                                       ` Miklos Szeredi
2020-08-12 17:39                                         ` Al Viro
2020-08-12 18:33                                           ` Al Viro
2020-08-12 21:30                                             ` Al Viro
2020-08-18  9:41                                               ` Miklos Szeredi
2020-08-18  9:30                                             ` Miklos Szeredi
2020-08-12 15:22                                   ` David Howells
2020-08-11 21:20                     ` Al Viro
2020-08-11 21:35                     ` Casey Schaufler
2020-08-11 16:05               ` Al Viro
2020-08-11 16:09                 ` Linus Torvalds
2020-08-11 16:39                   ` Al Viro
2020-08-12 10:14               ` Karel Zak
2020-08-12 13:09                 ` Miklos Szeredi
2020-08-12 13:33                 ` David Howells
2020-08-12 13:54                   ` Miklos Szeredi
2020-08-12  0:05             ` David Howells
2020-08-12  7:55               ` Miklos Szeredi
2020-08-12  8:29               ` David Howells
2020-08-12  8:37                 ` Miklos Szeredi
2020-08-12  9:43                   ` file metadata via fs API Steven Whitehouse
2020-08-12 10:04                     ` Miklos Szeredi
2020-08-12 11:28                       ` Karel Zak
2020-08-12 12:43                         ` Miklos Szeredi
2020-08-13  8:52                           ` Karel Zak
2020-08-12 13:06                         ` David Howells
2020-08-13  1:01                           ` Ian Kent
2020-08-12 18:18               ` file metadata via fs API (was: [GIT PULL] Filesystem Information) Linus Torvalds
2020-08-12 19:34                 ` file metadata via fs API Steven Whitehouse
2020-08-12 19:50                   ` Linus Torvalds
2020-08-13  3:44                     ` Ian Kent
2020-08-13 10:36                     ` Karel Zak
2020-08-14  7:58                     ` Lennart Poettering
2020-08-17 11:32                     ` Steven Whitehouse
2020-08-17 17:15                       ` Linus Torvalds
2020-08-17 22:44                         ` Linus Torvalds
2020-08-18 12:50                           ` Miklos Szeredi
2020-08-18 18:51                             ` Linus Torvalds
2020-08-18 20:18                               ` Miklos Szeredi
2020-08-18 20:53                                 ` Linus Torvalds
2020-08-21 13:17                                   ` Miklos Szeredi
2020-08-19  2:29                               ` Al Viro
2020-08-13  3:53                 ` file metadata via fs API (was: [GIT PULL] Filesystem Information) Jeffrey E Altman
2020-08-14 17:05                   ` Linus Torvalds
2020-08-18 15:01                     ` Jeffrey E Altman
2020-08-14  8:06                 ` Lennart Poettering
2020-08-12 13:54             ` David Howells
2020-08-12 14:10               ` Miklos Szeredi
2020-08-12 14:23               ` David Howells
2020-08-03 22:48 ` [GIT PULL] Mount notifications Ian Kent

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