linux-kernel - Re: [Y2038] [PATCH 13/16] hfs/hfsplus: use 64-bit inode timestamps

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Message-Id: <09B5EC34-DE6B-4017-A842-7983E7874F98@dubeyko.com>
Date:   Wed, 13 Nov 2019 20:03:56 +0300
From:   Viacheslav Dubeyko <slava@...eyko.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        "Ernesto A. Fernández" 
        <ernesto.mnd.fernandez@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Y2038] [PATCH 13/16] hfs/hfsplus: use 64-bit inode timestamps



> On Nov 13, 2019, at 11:06 AM, Arnd Bergmann <arnd@...db.de> wrote:
> 
> On Wed, Nov 13, 2019 at 7:00 AM Viacheslav Dubeyko <slava@...eyko.com> wrote:
>>> On Nov 9, 2019, at 12:32 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>> * There are two time systems.  Both are based on seconds since
>>> * a particular time/date.
>>> - *   Unix:   unsigned lil-endian since 00:00 GMT, Jan. 1, 1970
>>> + *   Unix:   signed little-endian since 00:00 GMT, Jan. 1, 1970
>>> *    mac:    unsigned big-endian since 00:00 GMT, Jan. 1, 1904
>>> *
>>> + * HFS implementations are highly inconsistent, this one matches the
>>> + * traditional behavior of 64-bit Linux, giving the most useful
>>> + * time range between 1970 and 2106, by treating any on-disk timestamp
>>> + * under 2082844800U (Jan 1 1970) as a time between 2040 and 2106.
>>> */
>>> -#define __hfs_u_to_mtime(sec)        cpu_to_be32(sec + 2082844800U - sys_tz.tz_minuteswest * 60)
>>> -#define __hfs_m_to_utime(sec)        (be32_to_cpu(sec) - 2082844800U  + sys_tz.tz_minuteswest * 60)
>> 
>> I believe it makes sense to introduce some constant instead of hardcoded value (2082844800U and 60).
>> It will be easier to understand the code without necessity to take a look into the comments.
>> What do you think?
> 
> Every other user of sys_tz.tz_minuteswest uses a plain '60', I think that one
> is easy enough to understand from context. Naming the other constant
> is a good idea, I've now folded the change below into my patch.
> 
> Thanks for the review!
> 
>      Arnd
> 
> 8<-----
> diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
> index 26733051ee50..f71c384064c8 100644
> --- a/fs/hfs/hfs_fs.h
> +++ b/fs/hfs/hfs_fs.h
> @@ -247,22 +247,24 @@ extern void hfs_mark_mdb_dirty(struct super_block *sb);
>  *
>  * HFS implementations are highly inconsistent, this one matches the
>  * traditional behavior of 64-bit Linux, giving the most useful
>  * time range between 1970 and 2106, by treating any on-disk timestamp
> - * under 2082844800U (Jan 1 1970) as a time between 2040 and 2106.
> + * under HFS_UTC_OFFSET (Jan 1 1970) as a time between 2040 and 2106.
>  */
> +#define HFS_UTC_OFFSET 2082844800U
> +
> static inline time64_t __hfs_m_to_utime(__be32 mt)
> {
> -       time64_t ut = (u32)(be32_to_cpu(mt) - 2082844800U);
> +       time64_t ut = (u32)(be32_to_cpu(mt) - HFS_UTC_OFFSET);
> 
>        return ut + sys_tz.tz_minuteswest * 60;
> }
> 
> static inline __be32 __hfs_u_to_mtime(time64_t ut)
> {
>        ut -= sys_tz.tz_minuteswest * 60;
> 
> -       return cpu_to_be32(lower_32_bits(ut) + 2082844800U);
> +       return cpu_to_be32(lower_32_bits(ut) + HFS_UTC_OFFSET);
> }
> #define HFS_I(inode)   (container_of(inode, struct hfs_inode_info, vfs_inode))
> #define HFS_SB(sb)     ((struct hfs_sb_info *)(sb)->s_fs_info)
> 
> diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
> index 22d0a22c41a3..3b03fff68543 100644
> --- a/fs/hfsplus/hfsplus_fs.h
> +++ b/fs/hfsplus/hfsplus_fs.h
> @@ -538,20 +538,22 @@ int hfsplus_read_wrapper(struct super_block *sb);
>  *
>  * HFS+ implementations are highly inconsistent, this one matches the
>  * traditional behavior of 64-bit Linux, giving the most useful
>  * time range between 1970 and 2106, by treating any on-disk timestamp
> - * under 2082844800U (Jan 1 1970) as a time between 2040 and 2106.
> + * under HFSPLUS_UTC_OFFSET (Jan 1 1970) as a time between 2040 and 2106.
>  */
> +#define HFSPLUS_UTC_OFFSET 2082844800U
> +
> static inline time64_t __hfsp_mt2ut(__be32 mt)
> {
> -       time64_t ut = (u32)(be32_to_cpu(mt) - 2082844800U);
> +       time64_t ut = (u32)(be32_to_cpu(mt) - HFSPLUS_UTC_OFFSET);
> 
>        return ut;
> }
> 
> static inline __be32 __hfsp_ut2mt(time64_t ut)
> {
> -       return cpu_to_be32(lower_32_bits(ut) + 2082844800U);
> +       return cpu_to_be32(lower_32_bits(ut) + HFSPLUS_UTC_OFFSET);
> }
> 
> /* compatibility */
> #define hfsp_mt2ut(t)          (struct timespec64){ .tv_sec = __hfsp_mt2ut(t) }

Looks good for me. I like the patch.

Reviewed-by: Vyacheslav Dubeyko <slava@...eyko.com>

Thanks,
Vyacheslav Dubeyko.