From: Christian Brauner <christian.brauner@ubuntu.com>
To: Ian Kent <raven@themaw.net>
Cc: David Howells <dhowells@redhat.com>,
viro@zeniv.linux.org.uk, mszeredi@redhat.com,
christian@brauner.io, linux-api@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/19] VFS: Filesystem information and notifications [ver #16]
Date: Thu, 20 Feb 2020 10:09:39 +0100 [thread overview]
Message-ID: <20200220090939.4e2mpmdixcyruzda@wittgenstein> (raw)
In-Reply-To: <c9a6f929b57e0c21c8845c211d1e3eab09d09633.camel@themaw.net>
On Thu, Feb 20, 2020 at 12:42:15PM +0800, Ian Kent wrote:
> On Wed, 2020-02-19 at 15:46 +0100, Christian Brauner wrote:
> > On Tue, Feb 18, 2020 at 05:04:55PM +0000, David Howells wrote:
> > > Here are a set of patches that adds system calls, that (a) allow
> > > information about the VFS, mount topology, superblock and files to
> > > be
> > > retrieved and (b) allow for notifications of mount topology
> > > rearrangement
> > > events, mount and superblock attribute changes and other superblock
> > > events,
> > > such as errors.
> > >
> > > ============================
> > > FILESYSTEM INFORMATION QUERY
> > > ============================
> > >
> > > The first system call, fsinfo(), allows information about the
> > > filesystem at
> > > a particular path point to be queried as a set of attributes, some
> > > of which
> > > may have more than one value.
> > >
> > > Attribute values are of four basic types:
> > >
> > > (1) Version dependent-length structure (size defined by type).
> > >
> > > (2) Variable-length string (up to 4096, including NUL).
> > >
> > > (3) List of structures (up to INT_MAX size).
> > >
> > > (4) Opaque blob (up to INT_MAX size).
> >
> > I mainly have an organizational question. :) This is a huge patchset
> > with lots and lots of (good) features. Wouldn't it make sense to make
> > the fsinfo() syscall a completely separate patchset from the
> > watch_mount() and watch_sb() syscalls? It seems that they don't need
> > to
> > depend on each other at all. This would make reviewing this so much
> > nicer and likely would mean that fsinfo() could proceed a little
> > faster.
>
> The remainder of the fsinfo() series would need to remain useful
> if this was done.
>
> For context I want work on improving handling of large mount
> tables.
Yeah, I've talked to David about this; polling on a large mountinfo file
is not great, I agree.
>
> Ultimately I expect to solve a very long standing autofs problem
> of using large direct mount maps without prohibitive performance
> overhead (and there a lot of rather challenging autofs changes to
> do for this too) and I believe the fsinfo() system call, and
> related bits, is the way to do this.
>
> But improving the handling of large mount tables for autofs
> will have the side effect of improvements for other mount table
> users, even in the early stages of this work.
>
> For example I want to use this for mount table handling improvements
> in libmount. Clearly that ultimately needs mount change notification
> in the end but ...
>
> There's a bunch of things that need to be done alone the way
> to even get started.
>
> One thing that's needed is the ability to call fsinfo() to get
> information on a mount to avoid constant reading of the proc based
> mount table, which happens a lot (since the mount info. needs
> to be up to date) so systemd (and others) would see an improvement
> with the fsinfo() system call alone able to be used in libmount.
>
> But for the fsinfo() system call to be used for this the file
> system specific mount options need to also be obtained when
> using fsinfo(). That means the super block operation fsinfo uses
> to provide this must be implemented for at least most file systems.
>
> So separating out the notifications part, leaving whatever is needed
> to still be able to do this, should be fine and the system call
> would be immediately useful once the super operation is implemented
> for the needed file systems.
>
> Whether the implementation of the super operation should be done
> as part of this series is another question but would certainly
> be a challenge and make the series more complicated. But is needed
> for the change to be useful in my case.
I think what would might work - and what David had already brought up
briefly - is to either base the fsinfo branch on top of the mount
notificaiton branch or break the notification counters pieces into a
separate patch and base both mount notifications and fsinfo on top of
it.
Christian
next prev parent reply other threads:[~2020-02-20 9:09 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-18 17:04 [PATCH 00/19] VFS: Filesystem information and notifications [ver #16] David Howells
2020-02-18 17:05 ` [PATCH 01/19] vfs: syscall: Add fsinfo() to query filesystem information " David Howells
2020-02-19 16:31 ` Darrick J. Wong
2020-02-19 20:07 ` Jann Horn
2020-02-20 10:34 ` David Howells
2020-02-20 15:48 ` Darrick J. Wong
2020-02-20 11:03 ` David Howells
2020-02-20 14:54 ` Jann Horn
2020-02-20 15:31 ` Darrick J. Wong
2020-02-18 17:05 ` [PATCH 02/19] fsinfo: Add syscalls to other arches " David Howells
2020-02-21 14:51 ` Christian Brauner
2020-02-21 18:10 ` Geert Uytterhoeven
2020-02-18 17:05 ` [PATCH 03/19] fsinfo: Provide a bitmap of supported features " David Howells
2020-02-19 16:37 ` Darrick J. Wong
2020-02-20 12:22 ` David Howells
2020-02-18 17:05 ` [PATCH 04/19] vfs: Add mount change counter " David Howells
2020-02-21 14:48 ` Christian Brauner
2020-02-18 17:05 ` [PATCH 05/19] vfs: Introduce a non-repeating system-unique superblock ID " David Howells
2020-02-19 16:53 ` Darrick J. Wong
2020-02-20 12:45 ` David Howells
2020-02-18 17:05 ` [PATCH 06/19] vfs: Allow fsinfo() to look up a mount object by " David Howells
2020-02-21 15:09 ` Christian Brauner
2020-02-18 17:05 ` [PATCH 07/19] vfs: Allow mount information to be queried by fsinfo() " David Howells
2020-02-18 17:05 ` [PATCH 08/19] vfs: fsinfo sample: Mount listing program " David Howells
2020-02-18 17:06 ` [PATCH 09/19] fsinfo: Allow the mount topology propogation flags to be retrieved " David Howells
2020-02-18 17:06 ` [PATCH 10/19] fsinfo: Add API documentation " David Howells
2020-02-18 17:06 ` [PATCH 11/19] afs: Support fsinfo() " David Howells
2020-02-19 21:01 ` Jann Horn
2020-02-20 12:58 ` David Howells
2020-02-20 14:58 ` Jann Horn
2020-02-21 13:26 ` David Howells
2020-02-18 17:06 ` [PATCH 12/19] security: Add hooks to rule on setting a superblock or mount watch " David Howells
2020-02-18 17:06 ` [PATCH 13/19] vfs: Add a mount-notification facility " David Howells
2020-02-19 22:40 ` Jann Horn
2020-02-19 22:55 ` Jann Horn
2020-02-21 12:24 ` David Howells
2020-02-21 15:49 ` Jann Horn
2020-02-21 17:06 ` David Howells
2020-02-21 17:36 ` seq_lock and lockdep_is_held() assertions Jann Horn
2020-02-21 18:02 ` John Stultz
2020-02-18 17:06 ` [PATCH 14/19] notifications: sample: Display mount tree change notifications [ver #16] David Howells
2020-02-18 17:06 ` [PATCH 15/19] vfs: Add superblock " David Howells
2020-02-19 23:08 ` Jann Horn
2020-02-21 14:23 ` David Howells
2020-02-21 15:44 ` Jann Horn
2020-02-21 16:33 ` David Howells
2020-02-21 16:41 ` Jann Horn
2020-02-21 17:11 ` David Howells
2020-02-18 17:06 ` [PATCH 16/19] fsinfo: Provide superblock notification counter " David Howells
2020-02-18 17:07 ` [PATCH 17/19] notifications: sample: Display superblock notifications " David Howells
2020-02-18 17:07 ` [PATCH 18/19] ext4: Add example fsinfo information " David Howells
2020-02-19 17:04 ` Darrick J. Wong
2020-02-20 0:53 ` kbuild test robot
2020-02-21 14:43 ` David Howells
2020-02-21 16:26 ` Darrick J. Wong
2020-02-18 17:07 ` [PATCH 19/19] nfs: Add example filesystem " David Howells
2020-02-20 2:13 ` kbuild test robot
2020-02-20 2:20 ` kbuild test robot
2020-02-18 18:12 ` David Howells
2020-02-19 10:23 ` [PATCH 00/19] VFS: Filesystem information and notifications " Stefan Metzmacher
2020-02-19 14:46 ` Christian Brauner
2020-02-19 15:50 ` Darrick J. Wong
2020-02-20 4:42 ` Ian Kent
2020-02-20 9:09 ` Christian Brauner [this message]
2020-02-20 11:30 ` Ian Kent
2020-02-19 16:16 ` David Howells
2020-02-21 12:57 ` David Howells
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