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

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Date:   Fri, 3 Jan 2020 19:36:04 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Namjae Jeon <linkinjeon@...il.com>
Cc:     Namjae Jeon <namjae.jeon@...sung.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        gregkh@...uxfoundation.org, valdis.kletnieks@...edu, hch@....de,
        sj1557.seo@...sung.com
Subject: Re: [PATCH v9 09/13] exfat: add misc operations

On Thursday 02 January 2020 12:40:34 Pali Rohár wrote:
> On Thursday 02 January 2020 20:30:03 Namjae Jeon wrote:
> > 2020-01-02 18:19 GMT+09:00, Pali Rohár <pali.rohar@...il.com>:
> > > 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.
> > My bad, I will change it with time64_t.
> 
> Now I have looked into sources and time_t is just typedef from
> __kernel_old_time_t type. So it looks like that time64_t is the type
> which should be used in new code.
> 
> But somebody else should confirm this information.
> 
> > >
> > >> +
> > >> +	/* 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)
> > Okay.
> > >
> > >   #define UNIX_SECS_2108    4354819200LL
> > >
> > >> +		tp->second  = 59;
> > >> +		tp->minute  = 59;
> > >> +		tp->hour = 23;
> > >> +		tp->day  = 31;
> > >> +		tp->month  = 12;
> > >> +		tp->year = 127;
> > >> +		return;
> > >> +	}
> > Okay, I will check it.
> > Thanks for your review!

Also I think that you should apply this Arnd's patch:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=44f6b40c225eb8e82eba8fd96d8f3fb843bc5a09

And maybe it is a good idea to look at applied staging patches:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/drivers/staging/exfat

-- 
Pali Rohár
pali.rohar@...il.com

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