linux-kernel - Re: [PATCH v10 09/14] exfat: add misc operations

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Date:   Wed, 15 Jan 2020 14:50:10 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Namjae Jeon <linkinjeon@...il.com>,
        Namjae Jeon <namjae.jeon@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Valdis Kletnieks <valdis.kletnieks@...edu>,
        Christoph Hellwig <hch@....de>, sj1557.seo@...sung.com
Subject: Re: [PATCH v10 09/14] exfat: add misc operations

On Wed, Jan 15, 2020 at 2:38 PM Pali Rohár <pali.rohar@...il.com> wrote:
> On Wednesday 15 January 2020 22:30:59 Namjae Jeon wrote:
> > 2020-01-15 19:10 GMT+09:00, Arnd Bergmann <arnd@...db.de>:

> > It is not described in the specification. I don't know exactly what
> > the problem is because sys_tz.tz_minuteswest seems to work fine to me.
> > It can be random garbage value ?
> >
> > > so if there is a choice, falling back to UTC would
> > > be nicer.
> >
> > Okay.
>
> Arnd, what is the default value of sys_tz.tz_minuteswest? What is the
> benefit of not using it?
>
> I though that timezone mount option is just an old hack when userspace
> does not correctly set kernel's timezone and that this timezone mount
> option should be in most cases avoided.

The main problem is that it is system-wide and initialized at boot
time through settimeofday() to a timezone picked by the system
administrator.

However, in user space, every user may set their own timezone with
the 'TZ' variable, and the default timezone may be different inside of a
container based on the contents of /etc/timezone in its root directory.

> So also another question, what is benefit of having fs specific timezone
> mount option? As it is fs specific it means that it would be used so
> much.

You can use it to access removable media that were written in
a different timezone, or a partition that is shared with another OS
running on the same machine but with different timezone settings.

     Arnd