From: Miklos Szeredi <miklos@szeredi.hu>
To: Ian Kent <raven@themaw.net>
Cc: David Howells <dhowells@redhat.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
Steven Whitehouse <swhiteho@redhat.com>,
Miklos Szeredi <mszeredi@redhat.com>,
viro <viro@zeniv.linux.org.uk>,
Christian Brauner <christian@brauner.io>,
Jann Horn <jannh@google.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Linux API <linux-api@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH 00/17] VFS: Filesystem information and notifications [ver #17]
Date: Tue, 3 Mar 2020 08:46:09 +0100 [thread overview]
Message-ID: <CAJfpegtu6VqhPdcudu79TX3e=_NZaJ+Md3harBGV7Bg_-+fR8Q@mail.gmail.com> (raw)
In-Reply-To: <0403cda7345e34c800eec8e2870a1917a8c07e5c.camel@themaw.net>
On Tue, Mar 3, 2020 at 6:28 AM Ian Kent <raven@themaw.net> wrote:
>
> On Mon, 2020-03-02 at 10:09 +0100, Miklos Szeredi wrote:
> > On Fri, Feb 28, 2020 at 5:36 PM David Howells <dhowells@redhat.com>
> > wrote:
> > > sysfs also has some other disadvantages for this:
> > >
> > > (1) There's a potential chicken-and-egg problem in that you have
> > > to create a
> > > bunch of files and dirs in sysfs for every created mount and
> > > superblock
> > > (possibly excluding special ones like the socket mount) - but
> > > this
> > > includes sysfs itself. This might work - provided you create
> > > sysfs
> > > first.
> >
> > Sysfs architecture looks something like this (I hope Greg will
> > correct
> > me if I'm wrong):
> >
> > device driver -> kobj tree <- sysfs tree
> >
> > The kobj tree is created by the device driver, and the dentry tree is
> > created on demand from the kobj tree. Lifetime of kobjs is bound to
> > both the sysfs objects and the device but not the other way round.
> > I.e. device can go away while the sysfs object is still being
> > referenced, and sysfs can be freely mounted and unmounted
> > independently of device initialization.
> >
> > So there's no ordering requirement between sysfs mounts and other
> > mounts. I might be wrong on the details, since mounts are created
> > very early in the boot process...
> >
> > > (2) sysfs is memory intensive. The directory structure has to be
> > > backed by
> > > dentries and inodes that linger as long as the referenced
> > > object does
> > > (procfs is more efficient in this regard for files that aren't
> > > being
> > > accessed)
> >
> > See above: I don't think dentries and inodes are pinned, only kobjs
> > and their associated cruft. Which may be too heavy, depending on the
> > details of the kobj tree.
> >
> > > (3) It gives people extra, indirect ways to pin mount objects and
> > > superblocks.
> >
> > See above.
> >
> > > For the moment, fsinfo() gives you three ways of referring to a
> > > filesystem
> > > object:
> > >
> > > (a) Directly by path.
> >
> > A path is always representable by an O_PATH descriptor.
> >
> > > (b) By path associated with an fd.
> >
> > See my proposal about linking from /proc/$PID/fdmount/$FD ->
> > /sys/devices/virtual/mounts/$MOUNT_ID.
> >
> > > (c) By mount ID (perm checked by working back up the tree).
> >
> > Check that perm on lookup of /sys/devices/virtual/mounts/$MOUNT_ID.
> > The proc symlink would bypass the lookup check by directly jumping to
> > the mountinfo dir.
> >
> > > but will need to add:
> > >
> > > (d) By fscontext fd (which is hard to find in sysfs). Indeed, the
> > > superblock
> > > may not even exist yet.
> >
> > Proc symlink would work for that too.
>
> There's mounts enumeration too, ordering is required to identify the
> top (or bottom depending on terminology) with more than one mount on
> a mount point.
>
> >
> > If sysfs is too heavy, this could be proc or a completely new
> > filesystem. The implementation is much less relevant at this stage
> > of
> > the discussion than the interface.
>
> Ha, proc with the seq file interface, that's already proved to not
> work properly and looks difficult to fix.
I'm doing a patch. Let's see how it fares in the face of all these
preconceptions.
Thanks,
Miklos
next prev parent reply other threads:[~2020-03-03 7:46 UTC|newest]
Thread overview: 117+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-21 18:01 [PATCH 00/17] VFS: Filesystem information and notifications [ver #17] David Howells
2020-02-21 18:01 ` [PATCH 01/17] watch_queue: Add security hooks to rule on setting mount and sb watches " David Howells
2020-02-21 18:02 ` [PATCH 02/17] watch_queue: Implement mount topology and attribute change notifications " David Howells
2020-02-21 18:02 ` [PATCH 03/17] watch_queue: sample: Display mount tree " David Howells
2020-02-21 18:02 ` [PATCH 04/17] watch_queue: Introduce a non-repeating system-unique superblock ID " David Howells
2020-02-21 18:02 ` [PATCH 05/17] watch_queue: Add superblock notifications " David Howells
2020-02-21 18:02 ` [PATCH 06/17] watch_queue: sample: Display " David Howells
2020-02-21 18:02 ` [PATCH 07/17] fsinfo: Add fsinfo() syscall to query filesystem information " David Howells
2020-02-26 2:29 ` Aleksa Sarai
2020-02-28 14:44 ` David Howells
2020-02-21 18:02 ` [PATCH 08/17] fsinfo: Provide a bitmap of supported features " David Howells
2020-02-21 18:03 ` [PATCH 09/17] fsinfo: Allow fsinfo() to look up a mount object by ID " David Howells
2020-02-21 18:03 ` [PATCH 10/17] fsinfo: Allow mount information to be queried " David Howells
2020-03-04 14:58 ` Miklos Szeredi
2020-03-04 16:10 ` Miklos Szeredi
2020-02-21 18:03 ` [PATCH 11/17] fsinfo: sample: Mount listing program " David Howells
2020-02-21 18:03 ` [PATCH 12/17] fsinfo: Allow the mount topology propogation flags to be retrieved " David Howells
2020-02-21 18:03 ` [PATCH 13/17] fsinfo: Query superblock unique ID and notification counter " David Howells
2020-02-21 18:03 ` [PATCH 14/17] fsinfo: Add API documentation " David Howells
2020-02-21 18:03 ` [PATCH 15/17] fsinfo: Add support for AFS " David Howells
2020-02-21 18:03 ` [PATCH 16/17] fsinfo: Add example support for Ext4 " David Howells
2020-02-21 18:04 ` [PATCH 17/17] fsinfo: Add example support for NFS " David Howells
2020-02-21 20:21 ` [PATCH 00/17] VFS: Filesystem information and notifications " James Bottomley
2020-02-24 10:24 ` Miklos Szeredi
2020-02-24 14:55 ` James Bottomley
2020-02-24 15:28 ` Miklos Szeredi
2020-02-25 12:13 ` Steven Whitehouse
2020-02-25 15:28 ` James Bottomley
2020-02-25 15:47 ` Steven Whitehouse
2020-02-26 9:11 ` Miklos Szeredi
2020-02-26 10:51 ` Steven Whitehouse
2020-02-27 5:06 ` Ian Kent
2020-02-27 9:36 ` Miklos Szeredi
2020-02-27 11:34 ` Ian Kent
2020-02-27 13:45 ` Miklos Szeredi
2020-02-27 15:14 ` Karel Zak
2020-02-28 0:43 ` Ian Kent
2020-02-28 8:35 ` Miklos Szeredi
2020-02-28 12:27 ` Greg Kroah-Hartman
2020-02-28 16:24 ` Miklos Szeredi
2020-02-28 17:15 ` Al Viro
2020-03-02 8:43 ` Miklos Szeredi
2020-03-02 10:34 ` Karel Zak
2020-02-28 16:42 ` David Howells
2020-02-28 15:08 ` James Bottomley
2020-02-28 15:40 ` Miklos Szeredi
2020-02-28 0:12 ` Ian Kent
2020-02-28 15:52 ` Christian Brauner
2020-02-28 16:36 ` David Howells
2020-03-02 9:09 ` Miklos Szeredi
2020-03-02 9:38 ` Greg Kroah-Hartman
2020-03-03 5:27 ` Ian Kent
2020-03-03 7:46 ` Miklos Szeredi [this message]
2020-03-06 16:25 ` Miklos Szeredi
2020-03-06 19:43 ` Al Viro
2020-03-06 19:54 ` Miklos Szeredi
2020-03-06 19:58 ` Al Viro
2020-03-06 20:05 ` Al Viro
2020-03-06 20:11 ` Miklos Szeredi
2020-03-06 20:37 ` Al Viro
2020-03-06 20:38 ` Al Viro
2020-03-06 20:45 ` Al Viro
2020-03-06 20:49 ` Al Viro
2020-03-06 20:51 ` Miklos Szeredi
2020-03-06 21:28 ` Al Viro
2020-03-06 20:56 ` Al Viro
2020-03-06 20:51 ` Miklos Szeredi
2020-03-07 9:48 ` Greg Kroah-Hartman
2020-03-07 20:48 ` Miklos Szeredi
2020-03-03 9:12 ` David Howells
2020-03-03 9:26 ` Miklos Szeredi
2020-03-03 9:48 ` Miklos Szeredi
2020-03-03 10:21 ` Steven Whitehouse
2020-03-03 10:32 ` Miklos Szeredi
2020-03-03 11:09 ` Ian Kent
2020-03-03 10:00 ` Christian Brauner
2020-03-03 10:13 ` Miklos Szeredi
2020-03-03 10:25 ` Christian Brauner
2020-03-03 11:33 ` Miklos Szeredi
2020-03-03 11:56 ` Christian Brauner
2020-03-03 11:38 ` Karel Zak
2020-03-03 13:03 ` Greg Kroah-Hartman
2020-03-03 13:14 ` Greg Kroah-Hartman
2020-03-03 13:34 ` Miklos Szeredi
2020-03-03 13:43 ` Greg Kroah-Hartman
2020-03-03 14:10 ` Greg Kroah-Hartman
2020-03-03 14:13 ` Jann Horn
2020-03-03 14:24 ` Greg Kroah-Hartman
2020-03-03 15:44 ` Jens Axboe
2020-03-03 16:37 ` Greg Kroah-Hartman
2020-03-03 16:51 ` Jeff Layton
2020-03-03 16:55 ` Jens Axboe
2020-03-03 19:02 ` Jeff Layton
2020-03-03 19:07 ` Jens Axboe
2020-03-03 19:23 ` Jens Axboe
2020-03-03 19:43 ` Jeff Layton
2020-03-03 20:33 ` Jens Axboe
2020-03-03 21:03 ` Jeff Layton
2020-03-03 21:20 ` Jens Axboe
2020-03-03 14:10 ` Miklos Szeredi
2020-03-03 14:29 ` Greg Kroah-Hartman
2020-03-03 14:40 ` Jann Horn
2020-03-03 16:51 ` Greg Kroah-Hartman
2020-03-03 16:57 ` Jann Horn
2020-03-03 20:15 ` Greg Kroah-Hartman
2020-03-03 14:40 ` David Howells
2020-03-04 4:20 ` Ian Kent
2020-03-03 14:19 ` David Howells
2020-03-03 16:59 ` Greg Kroah-Hartman
2020-03-03 14:23 ` Christian Brauner
2020-03-03 15:23 ` Greg Kroah-Hartman
2020-03-03 15:53 ` David Howells
2020-03-04 2:01 ` Ian Kent
2020-03-04 15:22 ` Karel Zak
2020-03-04 16:49 ` Greg Kroah-Hartman
2020-03-04 17:55 ` Karel Zak
2020-03-03 14:09 ` David Howells
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAJfpegtu6VqhPdcudu79TX3e=_NZaJ+Md3harBGV7Bg_-+fR8Q@mail.gmail.com' \
--to=miklos@szeredi.hu \
--cc=James.Bottomley@hansenpartnership.com \
--cc=christian.brauner@ubuntu.com \
--cc=christian@brauner.io \
--cc=darrick.wong@oracle.com \
--cc=dhowells@redhat.com \
--cc=gregkh@linuxfoundation.org \
--cc=jannh@google.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mszeredi@redhat.com \
--cc=raven@themaw.net \
--cc=swhiteho@redhat.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).