linux-kernel - Re: [PATCH 12/20] fs: fat: Initialize filesystem timestamp ranges

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Date:   Tue, 30 Jul 2019 10:39:41 -0700
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH 12/20] fs: fat: Initialize filesystem timestamp ranges

On Tue, Jul 30, 2019 at 2:31 AM OGAWA Hirofumi
<hirofumi@...l.parknet.co.jp> wrote:
>
> Deepa Dinamani <deepa.kernel@...il.com> writes:
>
> > +/* DOS dates from 1980/1/1 through 2107/12/31 */
> > +#define FAT_DATE_MIN (0<<9 | 1<<5 | 1)
> > +#define FAT_DATE_MAX (127<<9 | 12<<5 | 31)
> > +#define FAT_TIME_MAX (23<<11 | 59<<5 | 29)
> > +
> >  /*
> >   * A deserialized copy of the on-disk structure laid out in struct
> >   * fat_boot_sector.
> > @@ -1605,6 +1610,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
> >       int debug;
> >       long error;
> >       char buf[50];
> > +     struct timespec64 ts;
> >
> >       /*
> >        * GFP_KERNEL is ok here, because while we do hold the
> > @@ -1698,6 +1704,12 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
> >       sbi->free_clus_valid = 0;
> >       sbi->prev_free = FAT_START_ENT;
> >       sb->s_maxbytes = 0xffffffff;
> > +     fat_time_fat2unix(sbi, &ts, 0, cpu_to_le16(FAT_DATE_MIN), 0);
> > +     sb->s_time_min = ts.tv_sec;
> > +
> > +     fat_time_fat2unix(sbi, &ts, cpu_to_le16(FAT_TIME_MAX),
> > +                       cpu_to_le16(FAT_DATE_MAX), 0);
> > +     sb->s_time_max = ts.tv_sec;
>
> At least, it is wrong to call fat_time_fat2unix() before setup parameters
> in sbi.

All the parameters that fat_time_fat2unix() cares in sbi is accessed through

static inline int fat_tz_offset(struct msdos_sb_info *sbi)
{
    return (sbi->options.tz_set ?
           -sbi->options.time_offset :
           sys_tz.tz_minuteswest) * SECS_PER_MIN;
}

Both the sbi fields sbi->options.tz_set and sbi->options.time_offset
are set by the call to parse_options(). And, parse_options() is called
before the calls to fat_time_fat2unix().:

int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
           void (*setup)(struct super_block *))
{
     <snip>

    error = parse_options(sb, data, isvfat, silent, &debug, &sbi->options);
    if (error)
        goto out_fail;

   <snip>

    sbi->prev_free = FAT_START_ENT;
    sb->s_maxbytes = 0xffffffff;
    fat_time_fat2unix(sbi, &ts, 0, cpu_to_le16(FAT_DATE_MIN), 0);
    sb->s_time_min = ts.tv_sec;

    fat_time_fat2unix(sbi, &ts, cpu_to_le16(FAT_TIME_MAX),
              cpu_to_le16(FAT_DATE_MAX), 0);
    sb->s_time_max = ts.tv_sec;

   <snip>
}

I do not see what the problem is.

-Deepa