[PATCH] exfat: use local UTC offset when EXFAT_TZ_VALID isn't set

From: Chung-Chiang Cheng
Date: Thu Sep 09 2021 - 02:56:05 EST


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://docs.microsoft.com/en-us/windows/win32/fileio/exfat-specification#74102-offsetvalid-field
Signed-off-by: Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx>
---
fs/exfat/exfat_fs.h | 1 +
fs/exfat/misc.c | 8 +++++++-
fs/exfat/super.c | 3 ++-
3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 1d6da61157c9..b57fdd94ad01 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -204,6 +204,7 @@ struct exfat_mount_options {
/* on error: continue, panic, remount-ro */
enum exfat_error_mode errors;
unsigned utf8:1, /* Use of UTF-8 character set */
+ tz_set:1, /* Filesystem timestamps' offset set */
discard:1; /* Issue discard requests on deletions */
int time_offset; /* Offset of timestamps from UTC (in minutes) */
};
diff --git a/fs/exfat/misc.c b/fs/exfat/misc.c
index d34e6193258d..349e3fe64ea2 100644
--- a/fs/exfat/misc.c
+++ b/fs/exfat/misc.c
@@ -73,6 +73,12 @@ static void exfat_adjust_tz(struct timespec64 *ts, u8 tz_off)
ts->tv_sec += TIMEZONE_SEC(0x80 - tz_off);
}

+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;
+}
+
/* Convert a EXFAT time/date pair to a UNIX date (seconds since 1 1 70). */
void exfat_get_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
u8 tz, __le16 time, __le16 date, u8 time_cs)
@@ -96,7 +102,7 @@ void exfat_get_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
exfat_adjust_tz(ts, tz & ~EXFAT_TZ_VALID);
else
/* Convert from local time to UTC using time_offset. */
- ts->tv_sec -= sbi->options.time_offset * SECS_PER_MIN;
+ ts->tv_sec += exfat_tz_offset(sbi);
}

/* Convert linear UNIX date to a EXFAT time/date pair. */
diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index 5539ffc20d16..caeea375e4fa 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -173,7 +173,7 @@ static int exfat_show_options(struct seq_file *m, struct dentry *root)
seq_puts(m, ",errors=remount-ro");
if (opts->discard)
seq_puts(m, ",discard");
- if (opts->time_offset)
+ if (opts->tz_set)
seq_printf(m, ",time_offset=%d", opts->time_offset);
return 0;
}
@@ -303,6 +303,7 @@ static int exfat_parse_param(struct fs_context *fc, struct fs_parameter *param)
*/
if (result.int_32 < -24 * 60 || result.int_32 > 24 * 60)
return -EINVAL;
+ opts->tz_set = 1;
opts->time_offset = result.int_32;
break;
case Opt_utf8:
--
2.25.1