linux-ext4 - Re: Is labelling a mounted ext2/3/4 file system safe and supported?

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Date:   Tue, 27 Jul 2021 08:32:53 +0100
From:   Mike Fleetwood <mike.fleetwood@...glemail.com>
To:     Reindl Harald <h.reindl@...lounge.net>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: Is labelling a mounted ext2/3/4 file system safe and supported?

On Mon, 26 Jul 2021 at 21:50, Reindl Harald <h.reindl@...lounge.net> wrote:
> Am 26.07.21 um 20:45 schrieb Mike Fleetwood:
> > Hi,
> >
> > Using e2label to set a new label for a mounted ext4 seems to work, but
> > is it a safe and supported thing to do?
>
> it is

Is there some documentation which states it's safe to write to the label
while mounted?

I ask because 1) I am looking at adding such support into GParted and
2) I don't understand how it can be safe.

Looking at the e2label source code, it just reads the superblock,
updates the label and writes the super block.  How is that safe and
persistent when presumably the linux kernel has an in-memory copy of the
superblock will be written at unmount and presumable sync.

Thanks,
Mike