On Wed, Jan 15, 2020 at 9:28 AM Namjae Jeon <namjae.jeon@xxxxxxxxxxx> wrote:
> +#define SECS_PER_MIN (60)
> +#define TIMEZONE_SEC(x) ((x) * 15 * SECS_PER_MIN)
> +
> +static void exfat_adjust_tz(struct timespec64 *ts, u8 tz_off)
> +{
> + if (tz_off <= 0x3F)
> + ts->tv_sec -= TIMEZONE_SEC(tz_off);
> + else /* 0x40 <= (tz_off & 0x7F) <=0x7F */
> + ts->tv_sec += TIMEZONE_SEC(0x80 - tz_off);
> +}
> +
> +static inline int exfat_tz_offset(struct exfat_sb_info *sbi)
> +{
> + if (sbi->options.time_offset)
> + return sbi->options.time_offset;
> + return sys_tz.tz_minuteswest;
> +}
> +
> +/* 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,
> + __le16 time, __le16 date, u8 tz)
> +{
> + u16 t = le16_to_cpu(time);
> + u16 d = le16_to_cpu(date);
> +
> + ts->tv_sec = mktime64(1980 + (d >> 9), d >> 5 & 0x000F, d & 0x001F,
> + t >> 11, (t >> 5) & 0x003F, (t & 0x001F) << 1);
> + ts->tv_nsec = 0;
This part looks good to me now.
> + if (tz & EXFAT_TZ_VALID)
> + /* Treat as UTC time, but need to adjust timezone to UTC0 */
> + exfat_adjust_tz(ts, tz & ~EXFAT_TZ_VALID);
> + else
> + /* Treat as local time */
> + ts->tv_sec -= exfat_tz_offset(sbi) * SECS_PER_MIN;
> +}
Whereas this seems rather complex, when it deals with three different
cases:
- timezone stored in inode
- timezone offset passed as mount option
- local time from sys_tz.tz_minuteswest
Does the exfat specification require to use some notion of 'local time' here
as the fallback? The problem with sys_tz.tz_minuteswest is that it is
not too well-defined, so if there is a choice, falling back to UTC would
be nicer.
> +/* Convert linear UNIX date to a EXFAT time/date pair. */
> +void exfat_set_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
> + __le16 *time, __le16 *date, u8 *tz)
> +{
> + struct tm tm;
> + u16 t, d;
> +
> + /* clamp to the range valid in the exfat on-disk representation. */
> + time64_to_tm(clamp_t(time64_t, ts->tv_sec, EXFAT_MIN_TIMESTAMP_SECS,
> + EXFAT_MAX_TIMESTAMP_SECS), -exfat_tz_offset(sbi) * SECS_PER_MIN,
> + &tm);
I think you can drop the clamping here, as thes_time_min/s_time_max fields
should take care of that.
For writing out timestamps, it may be best to always encode them as UTC
and set set timezone-valid bit for that. That way, the min/max values
are known at compile time regardless of which time zone the machine
thinks it is in.
Arnd
