linux-kernel - Re: [RFC PATCH] getting misc stats/attributes via xattr API

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Date:   Thu, 5 May 2022 14:30:33 +0200
From:   Karel Zak <kzak@...hat.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     linux-fsdevel@...r.kernel.org, Dave Chinner <david@...morbit.com>,
        Theodore Ts'o <tytso@....edu>,
        Greg KH <gregkh@...uxfoundation.org>,
        Christian Brauner <brauner@...nel.org>,
        linux-kernel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        LSM <linux-security-module@...r.kernel.org>,
        Ian Kent <raven@...maw.net>,
        David Howells <dhowells@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Amir Goldstein <amir73il@...il.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [RFC PATCH] getting misc stats/attributes via xattr API

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@...hat.com>
 http://karelzak.blogspot.com