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Date:   Thu, 5 May 2022 14:30:33 +0200
From:   Karel Zak <kzak@redhat.com>
To:     Miklos Szeredi <miklos@szeredi.hu>
Cc:     linux-fsdevel@vger.kernel.org, Dave Chinner <david@fromorbit.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Greg KH <gregkh@linuxfoundation.org>,
        Christian Brauner <brauner@kernel.org>,
        linux-kernel@vger.kernel.org,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>,
        LSM <linux-security-module@vger.kernel.org>,
        Ian Kent <raven@themaw.net>,
        David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <christian@brauner.io>,
        Amir Goldstein <amir73il@gmail.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>
Subject: Re: [RFC PATCH] getting misc stats/attributes via xattr API
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On Tue, May 03, 2022 at 02:23:23PM +0200, Miklos Szeredi wrote:
> Examples:
> 
> $ getfattr -etext -n ":" .
> # file: .
> :="mnt:\000mntns:"
> 
> $ getfattr -etext -n ":mnt:" .
> # file: .
> :mnt:="info"
> 
> $ getfattr -etext -n ":mnt:info" .
> # file: .
> :mnt:info="21 1 254:0 / / rw,relatime - ext4 /dev/root rw\012"

Is there a way how to get mountinfo-like entry by mount ID for some
sub-tree? Something like:

 getfattr -etext -n ":mnt:info:21" /

The interface has to be consistent with some notification system (I
see your question about fsnotify/fanotify at linux-fsdevel) and mount
ID seems better than paths due to over-mounts, etc.

> $ getfattr -etext -n ":mntns:" .
> # file: .
> :mntns:="21:\00022:\00024:\00025:\00023:\00026:\00027:\00028:\00029:\00030:\00031:"
> 
> $ getfattr -etext -n ":mntns:28:" .
> # file: .
> :mntns:28:="info"

  Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com