linux-kernel - RE: [PATCH] exfat: use local UTC offset when EXFAT_TZ

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Message-ID: <c28301d7b99e$37fb5af0$a7f210d0$@samsung.com>
Date:   Tue, 5 Oct 2021 13:05:22 +0900
From:   "Sungjong Seo" <sj1557.seo@...sung.com>
To:     "'Namjae Jeon'" <linkinjeon@...nel.org>
Cc:     "'Chung-Chiang Cheng'" <cccheng@...ology.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <shepjeng@...il.com>, <sj1557.seo@...sung.com>
Subject: RE: [PATCH] exfat: use local UTC offset when EXFAT_TZ_VALID isn't
 set

> 2021-10-01 22:19 GMT+09:00, Sungjong Seo <sj1557.seo@...sung.com>:
> > Hello, Namjae,
> Hi Sungjong,
> >
> > I found an important difference between the code we first wrote and
> > the code that has changed since our initial patch review. This
> > difference seems to cause compatibility issues when reading saved
> timestamps without timezone.
> > (In our initial patch review, there were concerns about possible
> > compatibility issues.) I think the code that reads timestamps without
> > timezone should go back to the concept we wrote in the first place
> > like reported patch.
> Are you talking about using sys_tz?
Yes, exactly, a part like below.

+static inline int exfat_tz_offset(struct exfat_sb_info *sbi) {
+	return (sbi->options.tz_set ? -sbi->options.time_offset :
+			sys_tz.tz_minuteswest) * SECS_PER_MIN; }
+

> 
> > It could be an answer of another timestamp issue.
> What is another timestamp issue ?

What I'm saying is "timestamp incompatibilities in exfat-fs" from Reiner <reinerstallknecht@...il.com>
I think it might be the same issue with this.

> 
> >
> > Could you please let me know what you think?
> >
> > Thanks.
> >> -----Original Message-----
> >> From: Namjae Jeon [mailto:linkinjeon@...nel.org]
> >> Sent: Friday, September 10, 2021 10:01 AM
> >> To: Chung-Chiang Cheng <cccheng@...ology.com>
> >> Cc: sj1557.seo@...sung.com; linux-fsdevel@...r.kernel.org; linux-
> >> kernel@...r.kernel.org; shepjeng@...il.com
> >> Subject: Re: [PATCH] exfat: use local UTC offset when EXFAT_TZ_VALID
> >> isn't set
> >>
> >> 2021-09-09 15:55 GMT+09:00, Chung-Chiang Cheng <cccheng@...ology.com>:
> >> > EXFAT_TZ_VALID is corresponding to OffsetValid field in exfat
> >> > specification [1]. If this bit isn't set, timestamps should be
> >> > treated as having the same UTC offset as the current local time.
> >> >
> >> > This patch uses the existing mount option 'time_offset' as fat does.
> >> > If time_offset isn't set, local UTC offset in sys_tz will be used
> >> > as the default value.
> >> >
> >> > Link: [1]
> >> > https://protect2.fireeye.com/v1/url?k=cba4edf5-943fd4c8-cba566ba-0c
> >> > c47
> >> > a31309a-e70aa065be678729&q=1&e=225feff2-841f-404c-9a2e-c12064b232d0
> >> > &u=
> >> > https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Fwindows%2Fwin32%2Ffileio
> >> > %2F exfat-specification%2374102-offsetvalid-field
> >> > Signed-off-by: Chung-Chiang Cheng <cccheng@...ology.com>
> >> Please read this discussion:
> >>  https://patchwork.kernel.org/project/linux-
> >> fsdevel/patch/20200115082447.19520-10-namjae.jeon@...sung.com/
> >>
> >> Thanks!
> >
> >