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

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Date:   Thu, 2 Jan 2020 10:19:02 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Namjae Jeon <namjae.jeon@...sung.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        gregkh@...uxfoundation.org, valdis.kletnieks@...edu, hch@....de,
        sj1557.seo@...sung.com, linkinjeon@...il.com
Subject: Re: [PATCH v9 09/13] exfat: add misc operations

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@...sung.com>
> Signed-off-by: Sungjong Seo <sj1557.seo@...sung.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@...il.com