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From: Miklos Szeredi <miklos@szeredi.hu>
To: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: David Howells <dhowells@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Eric Biggers <ebiggers@kernel.org>,
	Jeff Layton <jlayton@kernel.org>,
	linux-ext4@vger.kernel.org,
	Carlos Maiolino <cmaiolino@redhat.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Linux API <linux-api@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ian Kent <raven@themaw.net>, Miklos Szeredi <mszeredi@redhat.com>,
	Christian Brauner <christian@brauner.io>,
	Jann Horn <jannh@google.com>, Karel Zak <kzak@redhat.com>,
	Jeff Layton <jlayton@redhat.com>,
	linux-fsdevel@vger.kernel.org,
	LSM <linux-security-module@vger.kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/18] VFS: Filesystem information [ver #21]
Date: Tue, 4 Aug 2020 21:18:38 +0200	[thread overview]
Message-ID: <CAJfpegtbX4DZcEuyF1oBatP__jRc_=HFmcJE8XUHjy1rwtqdOg@mail.gmail.com> (raw)
In-Reply-To: <1596555579.10158.23.camel@HansenPartnership.com>

On Tue, Aug 4, 2020 at 5:40 PM James Bottomley
<James.Bottomley@hansenpartnership.com> wrote:
>
> On Mon, 2020-08-03 at 14:36 +0100, David Howells wrote:
> > Here's a set of patches that adds a system call, fsinfo(), that
> > allows information about the VFS, mount topology, superblock and
> > files to be retrieved.
> >
> > The patchset is based on top of the notifications patchset and allows
> > event counters implemented in the latter to be retrieved to allow
> > overruns to be efficiently managed.
>
> Could I repeat the question I asked about six months back that never
> got answered:
>
> https://lore.kernel.org/linux-api/1582316494.3376.45.camel@HansenPartnership.com/
>
> It sort of petered out into a long winding thread about why not use
> sysfs instead, which really doesn't look like a good idea to me.
>
> I'll repeat the information for those who want to quote it easily on
> reply without having to use a web interface:
>
> ---
> Could I make a suggestion about how this should be done in a way that
> doesn't actually require the fsinfo syscall at all: it could just be
> done with fsconfig.  The idea is based on something I've wanted to do
> for configfd but couldn't because otherwise it wouldn't substitute for
> fsconfig, but Christian made me think it was actually essential to the
> ability of the seccomp and other verifier tools in the critique of
> configfd and I belive the same critique applies here.
>
> Instead of making fsconfig functionally configure ... as in you pass
> the attribute name, type and parameters down into the fs specific
> handler and the handler does a string match and then verifies the
> parameters and then acts on them, make it table configured, so what
> each fstype does is register a table of attributes which can be got and
> optionally set (with each attribute having a get and optional set
> function).  We'd have multiple tables per fstype, so the generic VFS
> can register a table of attributes it understands for every fstype
> (things like name, uuid and the like) and then each fs type would
> register a table of fs specific attributes following the same pattern.
> The system would examine the fs specific table before the generic one,
> allowing overrides.  fsconfig would have the ability to both get and
> set attributes, permitting retrieval as well as setting (which is how I
> get rid of the fsinfo syscall), we'd have a global parameter, which
> would retrieve the entire table by name and type so the whole thing is
> introspectable because the upper layer knows a-priori all the
> attributes which can be set for a given fs type and what type they are
> (so we can make more of the parsing generic).  Any attribute which
> doesn't have a set routine would be read only and all attributes would
> have to have a get routine meaning everything is queryable.

fsconfig(2) takes an fd referring to an fs_context, that in turn
refers to a super_block.

So using fsconfig() for retrieving super_block attributes would be
fine (modulo value being const, and lack of buffer size).

But what about mount attributes?

I don't buy the argument that an API needs to be designed around the
requirements of seccomp and the like.  It should be the other way
round.  In that, I think your configfd idea was fine, and would answer
the above question.

Thanks,
Miklos

  reply	other threads:[~2020-08-04 19:18 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 13:36 David Howells
2020-08-03 13:36 ` [PATCH 01/18] fsinfo: Introduce a non-repeating system-unique superblock ID " David Howells
2020-08-04  9:34   ` Miklos Szeredi
2020-08-03 13:36 ` [PATCH 02/18] fsinfo: Add fsinfo() syscall to query filesystem information " David Howells
2020-08-04 10:16   ` Miklos Szeredi
2020-08-04 11:34   ` David Howells
2020-08-27 11:27   ` Michael Kerrisk (man-pages)
2020-08-03 13:36 ` [PATCH 03/18] fsinfo: Provide a bitmap of the features a filesystem supports " David Howells
2020-08-03 13:37 ` [PATCH 04/18] fsinfo: Allow retrieval of superblock devname, options and stats " David Howells
2020-08-03 13:37 ` [PATCH 05/18] fsinfo: Allow fsinfo() to look up a mount object by ID " David Howells
2020-08-04 10:33   ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 06/18] fsinfo: Add a uniquifier ID to struct mount " David Howells
2020-08-04 10:41   ` Miklos Szeredi
2020-08-04 12:32     ` Ian Kent
2020-08-05 14:13   ` David Howells
2020-08-05 14:46     ` Miklos Szeredi
2020-08-05 15:30     ` David Howells
2020-08-05 19:33       ` Matthew Wilcox
2020-08-06  5:43         ` Ian Kent
2020-08-03 13:37 ` [PATCH 07/18] fsinfo: Allow mount information to be queried " David Howells
2020-08-03 13:37 ` [PATCH 08/18] fsinfo: Allow mount topology and propagation info to be retrieved " David Howells
2020-08-04 13:38   ` Miklos Szeredi
2020-08-05 15:37   ` David Howells
2020-08-05 17:19     ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 09/18] watch_queue: Mount event counters " David Howells
2020-08-03 13:37 ` [PATCH 10/18] fsinfo: Provide notification overrun handling support " David Howells
2020-08-04 13:56   ` Miklos Szeredi
2020-08-05  2:05     ` Ian Kent
2020-08-05  2:46       ` Ian Kent
2020-08-05  7:45         ` Miklos Szeredi
2020-08-05 11:23           ` Ian Kent
2020-08-05 11:27             ` Miklos Szeredi
2020-08-06  1:47               ` Ian Kent
2020-08-05 16:06   ` David Howells
2020-08-05 17:26     ` Miklos Szeredi
2020-08-03 13:37 ` [PATCH 11/18] fsinfo: sample: Mount listing program " David Howells
2020-08-03 13:38 ` [PATCH 12/18] fsinfo: Add API documentation " David Howells
2020-08-03 13:38 ` [PATCH 13/18] fsinfo: Add support for AFS " David Howells
2020-08-03 13:38 ` [PATCH 14/18] fsinfo: Add support to ext4 " David Howells
2020-08-03 13:38 ` [PATCH 15/18] fsinfo: Add an attribute that lists all the visible mounts in a namespace " David Howells
2020-08-04 14:05   ` Miklos Szeredi
2020-08-05  0:59     ` Ian Kent
2020-08-05 16:44   ` David Howells
2020-08-03 13:38 ` [PATCH 16/18] errseq: add a new errseq_scrape function " David Howells
2020-08-03 13:38 ` [PATCH 17/18] vfs: allow fsinfo to fetch the current state of s_wb_err " David Howells
2020-08-03 13:39 ` [PATCH 18/18] samples: add error state information to test-fsinfo.c " David Howells
2020-08-04 15:39 ` [PATCH 00/18] VFS: Filesystem information " James Bottomley
2020-08-04 19:18   ` Miklos Szeredi [this message]
2020-08-05 17:13 ` David Howells

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