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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 12 Aug 2020 15:09:26 +0200
Message-ID: <CAJfpegs4gzvJMBz=su8KgXXxX41tv8tVhO88Eap9pDeHRaSDPA@mail.gmail.com>
Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information)
To:     Karel Zak <kzak@redhat.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@redhat.com>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Christian Brauner <christian@brauner.io>,
        Lennart Poettering <lennart@poettering.net>,
        Linux API <linux-api@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        LSM <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Wed, Aug 12, 2020 at 12:14 PM Karel Zak <kzak@redhat.com> wrote:

> For example,  by fsinfo(FSINFO_ATTR_MOUNT_TOPOLOGY) you get all
> mountpoint propagation setting and relations by one syscall,

That's just an arbitrary grouping of attributes.

You said yourself, that what's really needed is e.g. consistent
snapshot of a complete mount tree topology.  And to get the complete
topology FSINFO_ATTR_MOUNT_TOPOLOGY and FSINFO_ATTR_MOUNT_CHILDREN are
needed for *each* individual mount.  The topology can obviously change
between those calls.

So there's no fundamental difference between getting individual
attributes or getting attribute groups in this respect.

> It would be also nice to avoid some strings formatting and separators
> like we use in the current mountinfo.

I think quoting non-printable is okay.

> I can imagine multiple values separated by binary header (like we already
> have for watch_notification, inotify, etc):

Adding a few generic binary interfaces is okay.   Adding many
specialized binary interfaces is a PITA.

Thanks,
Miklos