Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CGME20200115082824epcas1p4eb45d088c2f88149acb94563c4a9b276@epcas1p4.samsung.com>
 <20200115082447.19520-1-namjae.jeon@samsung.com> <20200115082447.19520-10-namjae.jeon@samsung.com>
 <CAK8P3a3Vqz=T_=sFwBBPa2_Hi_dA=BwWod=L9JkLxUgi=aKNWw@mail.gmail.com>
 <CAKYAXd9_qmanQCcrdpScFWvPXuZvk4jhv7Gc=t_vRL9zqWNSjA@mail.gmail.com> <20200115133838.q33p5riihsinp6c4@pali>
In-Reply-To: <20200115133838.q33p5riihsinp6c4@pali>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 15 Jan 2020 14:50:10 +0100
Message-ID: <CAK8P3a1ozgLYpDtveU0CtLj5fEFG8i=_QrnEAtoVFt-yC=Dc0g@mail.gmail.com>
Subject: Re: [PATCH v10 09/14] exfat: add misc operations
To:     =?UTF-8?Q?Pali_Roh=C3=A1r?= <pali.rohar@gmail.com>
Cc:     Namjae Jeon <linkinjeon@gmail.com>,
        Namjae Jeon <namjae.jeon@samsung.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
        gregkh <gregkh@linuxfoundation.org>,
        Valdis Kletnieks <valdis.kletnieks@vt.edu>,
        Christoph Hellwig <hch@lst.de>, sj1557.seo@samsung.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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