Re: [PATCH v9 09/13] exfat: add misc operations

[Christoph Hellwig <hch@lst.de>]

Arnd, can you review the exfat time handling, especially vs y2038
related issues?

On Thu, Jan 02, 2020 at 10:19:02AM +0100, Pali Rohár wrote:
> On Thursday 02 January 2020 16:20:32 Namjae Jeon wrote:
> > This adds the implementation of misc operations for exfat.
> > 
> > Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> > Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
> > ---
> >  fs/exfat/misc.c | 253 ++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 253 insertions(+)
> >  create mode 100644 fs/exfat/misc.c
> > 
> > diff --git a/fs/exfat/misc.c b/fs/exfat/misc.c
> > new file mode 100644
> > index 000000000000..7f533bcb3b3f
> > --- /dev/null
> > +++ b/fs/exfat/misc.c
> 
> ...
> 
> > +/* <linux/time.h> externs sys_tz
> > + * extern struct timezone sys_tz;
> > + */
> > +#define UNIX_SECS_1980    315532800L
> > +
> > +#if BITS_PER_LONG == 64
> > +#define UNIX_SECS_2108    4354819200L
> > +#endif
> 
> ...
> 
> > +#define TIMEZONE_CUR_OFFSET()	((sys_tz.tz_minuteswest / (-15)) & 0x7F)
> > +/* Convert linear UNIX date to a FAT time/date pair. */
> > +void exfat_time_unix2fat(struct exfat_sb_info *sbi, struct timespec64 *ts,
> > +		struct exfat_date_time *tp)
> > +{
> > +	time_t second = ts->tv_sec;
> > +	time_t day, month, year;
> > +	time_t ld; /* leap day */
> 
> Question for other maintainers: Has kernel code already time_t defined
> as 64bit? Or it is still just 32bit and 32bit systems and some time64_t
> needs to be used? I remember that there was discussion about these
> problems, but do not know if it was changed/fixed or not... Just a
> pointer for possible Y2038 problem. As "ts" is of type timespec64, but
> "second" of type time_t.
> 
> > +
> > +	/* Treats as local time with proper time */
> > +	second -= sys_tz.tz_minuteswest * SECS_PER_MIN;
> > +	tp->timezone.valid = 1;
> > +	tp->timezone.off = TIMEZONE_CUR_OFFSET();
> > +
> > +	/* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
> > +	if (second < UNIX_SECS_1980) {
> > +		tp->second  = 0;
> > +		tp->minute  = 0;
> > +		tp->hour = 0;
> > +		tp->day  = 1;
> > +		tp->month  = 1;
> > +		tp->year = 0;
> > +		return;
> > +	}
> > +
> > +	if (second >= UNIX_SECS_2108) {
> 
> Hello, this code cause compile errors on 32bit systems as UNIX_SECS_2108
> macro is not defined when BITS_PER_LONG == 32.
> 
> Value 4354819200 really cannot fit into 32bit signed integer, so you
> should use 64bit signed integer. I would suggest to define this macro
> value via LL not just L suffix (and it would work on both 32 and 64bit)
> 
>   #define UNIX_SECS_2108    4354819200LL
> 
> > +		tp->second  = 59;
> > +		tp->minute  = 59;
> > +		tp->hour = 23;
> > +		tp->day  = 31;
> > +		tp->month  = 12;
> > +		tp->year = 127;
> > +		return;
> > +	}
> 
> -- 
> Pali Rohár
> pali.rohar@gmail.com
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