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From: David Howells <dhowells@redhat.com>
To: Jann Horn <jannh@google.com>
Cc: dhowells@redhat.com, Al Viro <viro@zeniv.linux.org.uk>,
	raven@themaw.net, Miklos Szeredi <mszeredi@redhat.com>,
	Christian Brauner <christian@brauner.io>,
	Linux API <linux-api@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 11/19] afs: Support fsinfo() [ver #16]
Date: Thu, 20 Feb 2020 12:58:52 +0000	[thread overview]
Message-ID: <628199.1582203532@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAG48ez0fsB_XTmNfE-2tuabH7JHyQdih8bu7Qwu9HGWJXti7tQ@mail.gmail.com>

Jann Horn <jannh@google.com> wrote:

> Ewww. So basically, having one static set of .fsinfo_attributes is not
> sufficiently flexible for everyone, but instead of allowing the
> filesystem to dynamically provide a list of supported attributes, you
> just duplicate the super_operations? Seems to me like it'd be cleaner
> to add a function pointer to the super_operations that can dynamically
> fill out the supported fsinfo attributes.
>
> It seems to me like the current API is going to be a dead end if you
> ever want to have decent passthrough of these things for e.g. FUSE, or
> overlayfs, or VirtFS?

Ummm...

Would it be sufficient to have a function that returns a list of attributes?
Or does it need to be able to call to vfs_do_fsinfo() if it supports an
attribute?

There are two things I want to be able to do:

 (1) Do the buffer wrangling in the core - which means the core needs to see
     the type of the attribute.  That's fine if, say, afs_fsinfo() can call
     vfs_do_fsinfo() with the definition for any attribute it wants to handle
     and, say, return -ENOPKG otherways so that the core can then fall back to
     its private list.

 (2) Be able to retrieve the list of attributes and/or query an attribute.
     Now, I can probably manage this even through the same interface.  If,
     say, seeing FSINFO_ATTR_FSINFO_ATTRIBUTES causes the handler to simply
     append on the IDs of its own supported attributes (a helper can be
     provided for that).

     If it sees FSINFO_ATR_FSINFO_ATTRIBUTE_INFO, it can just look to see if
     it has the attribute with the ID matching Nth and return that, else
     ENOPKG - again a helper could be provided.

Chaining through overlayfs gets tricky.  You end up with multiple contributory
filesystems with different properties - and any one of those layers could
perhaps be another overlay.  Overlayfs would probably needs to integrate the
info and derive the lowest common set.

David


  parent reply	other threads:[~2020-02-20 12:59 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 [this message]
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
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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