From: Jann Horn <jannh@google.com>
To: David Howells <dhowells@redhat.com>
Cc: 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 15:58:10 +0100 [thread overview]
Message-ID: <CAG48ez03VMKEmJEmViSkxbF9J5dW=6vny9vKGdenBewtjF+nqQ@mail.gmail.com> (raw)
In-Reply-To: <628199.1582203532@warthog.procyon.org.uk>
On Thu, Feb 20, 2020 at 1:59 PM David Howells <dhowells@redhat.com> wrote:
> 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.
Hm - I guess just returning a list of attributes ought to be fine?
Then AFS can just return one of its two statically-allocated attribute
lists there, and a filesystem with more complicated circumstances
(like FUSE or overlayfs or whatever) can compute a heap-allocated list
on mount that is freed when the superblock goes away, or something
like that?
next prev parent reply other threads:[~2020-02-20 14:58 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 [this message]
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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