Message-Id: <2520E708-4636-4CA8-B953-0F46F8E7454A@dubeyko.com>
Date:   Wed, 13 Nov 2019 08:59:58 +0300
From:   Viacheslav Dubeyko <slava@...eyko.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     y2038@...ts.linaro.org, LKML <linux-kernel@...r.kernel.org>,
        "Ernesto A. Fernández" 
        <ernesto.mnd.fernandez@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 13/16] hfs/hfsplus: use 64-bit inode timestamps



> On Nov 9, 2019, at 12:32 AM, Arnd Bergmann <arnd@...db.de> wrote:
> 
> The interpretation of on-disk timestamps in HFS and HFS+ differs
> between 32-bit and 64-bit kernels at the moment. Use 64-bit timestamps
> consistently so apply the current 64-bit behavior everyhere.
> 
> According to the official documentation for HFS+ [1], inode timestamps
> are supposed to cover the time range from 1904 to 2040 as originally
> used in classic MacOS.
> 
> The traditional Linux usage is to convert the timestamps into an unsigned
> 32-bit number based on the Unix epoch and from there to a time_t. On
> 32-bit systems, that wraps the time from 2038 to 1902, so the last
> two years of the valid time range become garbled. On 64-bit systems,
> all times before 1970 get turned into timestamps between 2038 and 2106,
> which is more convenient but also different from the documented behavior.
> 
> Looking at the Darwin sources [2], it seems that MacOS is inconsistent in
> yet another way: all timestamps are wrapped around to a 32-bit unsigned
> number when written to the disk, but when read back, all numeric values
> lower than 2082844800U are assumed to be invalid, so we cannot represent
> the times before 1970 or the times after 2040.
> 
> While all implementations seem to agree on the interpretation of values
> between 1970 and 2038, they often differ on the exact range they support
> when reading back values outside of the common range:
> 
> MacOS (traditional):		1904-2040
> Apple Documentation:		1904-2040
> MacOS X source comments:	1970-2040
> MacOS X source code:		1970-2038
> 32-bit Linux:			1902-2038
> 64-bit Linux:			1970-2106
> hfsfuse:			1970-2040
> hfsutils (32 bit, old libc)	1902-2038
> hfsutils (32 bit, new libc)	1970-2106
> hfsutils (64 bit)		1904-2040
> hfsplus-utils			1904-2040
> hfsexplorer			1904-2040
> 7-zip				1904-2040
> 
> Out of the above, the range from 1970 to 2106 seems to be the most useful,
> as it allows using HFS and HFS+ beyond year 2038, and this matches the
> behavior that most users would see today on Linux, as few people run
> 32-bit kernels any more.
> 
> Link: [1] https://developer.apple.com/library/archive/technotes/tn/tn1150.html
> Link: [2] https://opensource.apple.com/source/hfs/hfs-407.30.1/core/MacOSStubs.c.auto.html
> Link: https://lore.kernel.org/lkml/20180711224625.airwna6gzyatoowe@eaf/
> Cc: Viacheslav Dubeyko <slava@...eyko.com>
> Suggested-by: "Ernesto A. Fernández" <ernesto.mnd.fernandez@...il.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v3: revert back to 1970-2106 time range
>    fix bugs found in review
>    merge both patches into one
>    drop cc:stable tag
> v2: treat pre-1970 dates as invalid following MacOS X behavior,
>    reword and expand changelog text
> ---
> fs/hfs/hfs_fs.h         | 26 ++++++++++++++++++++------
> fs/hfs/inode.c          |  4 ++--
> fs/hfsplus/hfsplus_fs.h | 26 +++++++++++++++++++++-----
> fs/hfsplus/inode.c      | 12 ++++++------
> 4 files changed, 49 insertions(+), 19 deletions(-)
> 
> diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
> index 6d0783e2e276..26733051ee50 100644
> --- a/fs/hfs/hfs_fs.h
> +++ b/fs/hfs/hfs_fs.h
> @@ -242,19 +242,33 @@ extern void hfs_mark_mdb_dirty(struct super_block *sb);
> /*
>  * 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?

> +static inline time64_t __hfs_m_to_utime(__be32 mt)
> +{
> +	time64_t ut = (u32)(be32_to_cpu(mt) - 2082844800U);

Ditto.

> +
> +	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);

Ditto.

> +}
> #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)
> 
> -#define hfs_m_to_utime(time)	(struct timespec){ .tv_sec = __hfs_m_to_utime(time) }
> -#define hfs_u_to_mtime(time)	__hfs_u_to_mtime((time).tv_sec)
> -#define hfs_mtime()		__hfs_u_to_mtime(get_seconds())
> +#define hfs_m_to_utime(time)   (struct timespec64){ .tv_sec = __hfs_m_to_utime(time) }
> +#define hfs_u_to_mtime(time)   __hfs_u_to_mtime((time).tv_sec)
> +#define hfs_mtime()		__hfs_u_to_mtime(ktime_get_real_seconds())
> 
> static inline const char *hfs_mdb_name(struct super_block *sb)
> {
> diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
> index da243c84e93b..2f224b98ee94 100644
> --- a/fs/hfs/inode.c
> +++ b/fs/hfs/inode.c
> @@ -351,7 +351,7 @@ static int hfs_read_inode(struct inode *inode, void *data)
> 		inode->i_mode &= ~hsb->s_file_umask;
> 		inode->i_mode |= S_IFREG;
> 		inode->i_ctime = inode->i_atime = inode->i_mtime =
> -				timespec_to_timespec64(hfs_m_to_utime(rec->file.MdDat));
> +				hfs_m_to_utime(rec->file.MdDat);
> 		inode->i_op = &hfs_file_inode_operations;
> 		inode->i_fop = &hfs_file_operations;
> 		inode->i_mapping->a_ops = &hfs_aops;
> @@ -362,7 +362,7 @@ static int hfs_read_inode(struct inode *inode, void *data)
> 		HFS_I(inode)->fs_blocks = 0;
> 		inode->i_mode = S_IFDIR | (S_IRWXUGO & ~hsb->s_dir_umask);
> 		inode->i_ctime = inode->i_atime = inode->i_mtime =
> -				timespec_to_timespec64(hfs_m_to_utime(rec->dir.MdDat));
> +				hfs_m_to_utime(rec->dir.MdDat);
> 		inode->i_op = &hfs_dir_inode_operations;
> 		inode->i_fop = &hfs_dir_operations;
> 		break;
> diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
> index b8471bf05def..22d0a22c41a3 100644
> --- a/fs/hfsplus/hfsplus_fs.h
> +++ b/fs/hfsplus/hfsplus_fs.h
> @@ -533,13 +533,29 @@ int hfsplus_submit_bio(struct super_block *sb, sector_t sector, void *buf,
> 		       void **data, int op, int op_flags);
> int hfsplus_read_wrapper(struct super_block *sb);
> 
> -/* time macros */
> -#define __hfsp_mt2ut(t)		(be32_to_cpu(t) - 2082844800U)
> -#define __hfsp_ut2mt(t)		(cpu_to_be32(t + 2082844800U))

Ditto.

> +/*
> + * time helpers: convert between 1904-base and 1970-base timestamps
> + *
> + * 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.
> + */
> +static inline time64_t __hfsp_mt2ut(__be32 mt)
> +{
> +	time64_t ut = (u32)(be32_to_cpu(mt) - 2082844800U);

Ditto.

> +
> +	return ut;
> +}
> +
> +static inline __be32 __hfsp_ut2mt(time64_t ut)
> +{
> +	return cpu_to_be32(lower_32_bits(ut) + 2082844800U);

Ditto.

> +}
> 
> /* compatibility */
> -#define hfsp_mt2ut(t)		(struct timespec){ .tv_sec = __hfsp_mt2ut(t) }
> +#define hfsp_mt2ut(t)		(struct timespec64){ .tv_sec = __hfsp_mt2ut(t) }
> #define hfsp_ut2mt(t)		__hfsp_ut2mt((t).tv_sec)
> -#define hfsp_now2mt()		__hfsp_ut2mt(get_seconds())
> +#define hfsp_now2mt()		__hfsp_ut2mt(ktime_get_real_seconds())
> 
> #endif
> diff --git a/fs/hfsplus/inode.c b/fs/hfsplus/inode.c
> index d131c8ea7eb6..94bd83b36644 100644
> --- a/fs/hfsplus/inode.c
> +++ b/fs/hfsplus/inode.c
> @@ -504,9 +504,9 @@ int hfsplus_cat_read_inode(struct inode *inode, struct hfs_find_data *fd)
> 		hfsplus_get_perms(inode, &folder->permissions, 1);
> 		set_nlink(inode, 1);
> 		inode->i_size = 2 + be32_to_cpu(folder->valence);
> -		inode->i_atime = timespec_to_timespec64(hfsp_mt2ut(folder->access_date));
> -		inode->i_mtime = timespec_to_timespec64(hfsp_mt2ut(folder->content_mod_date));
> -		inode->i_ctime = timespec_to_timespec64(hfsp_mt2ut(folder->attribute_mod_date));
> +		inode->i_atime = hfsp_mt2ut(folder->access_date);
> +		inode->i_mtime = hfsp_mt2ut(folder->content_mod_date);
> +		inode->i_ctime = hfsp_mt2ut(folder->attribute_mod_date);
> 		HFSPLUS_I(inode)->create_date = folder->create_date;
> 		HFSPLUS_I(inode)->fs_blocks = 0;
> 		if (folder->flags & cpu_to_be16(HFSPLUS_HAS_FOLDER_COUNT)) {
> @@ -542,9 +542,9 @@ int hfsplus_cat_read_inode(struct inode *inode, struct hfs_find_data *fd)
> 			init_special_inode(inode, inode->i_mode,
> 					   be32_to_cpu(file->permissions.dev));
> 		}
> -		inode->i_atime = timespec_to_timespec64(hfsp_mt2ut(file->access_date));
> -		inode->i_mtime = timespec_to_timespec64(hfsp_mt2ut(file->content_mod_date));
> -		inode->i_ctime = timespec_to_timespec64(hfsp_mt2ut(file->attribute_mod_date));
> +		inode->i_atime = hfsp_mt2ut(file->access_date);
> +		inode->i_mtime = hfsp_mt2ut(file->content_mod_date);
> +		inode->i_ctime = hfsp_mt2ut(file->attribute_mod_date);
> 		HFSPLUS_I(inode)->create_date = file->create_date;
> 	} else {
> 		pr_err("bad catalog entry used to create inode\n");
> — 
> 2.20.0
> 

The patch looks pretty clean and good.

Thanks,
Viacheslav Dubeyko.

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