linux-kernel - Re: [PATCH 1/3] hfs: stop using timespec based interfaces

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Message-ID: <1529427809.2624.16.camel@dubeyko.com>
Date:   Tue, 19 Jun 2018 10:03:29 -0700
From:   Viacheslav Dubeyko <slava@...eyko.com>
To:     Arnd Bergmann <arnd@...db.de>, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     y2038@...ts.linaro.org, Jeff Layton <jlayton@...hat.com>,
        Jan Kara <jack@...e.cz>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] hfs: stop using timespec based interfaces

On Tue, 2018-06-19 at 18:02 +0200, Arnd Bergmann wrote:
> The native HFS timestamps overflow in year 2040, two years after the
> Unix
> y2038 overflow. However, the way that the conversion between on-disk
> timestamps and in-kernel timestamps was implemented, 64-bit machines
> actually ended up converting negative UTC timestamps (1902 through
> 1969)
> into times between 2038 and 2106.
> 
> Rather than making all machines faithfully represent timestamps in
> the
> ancient past but break after 2040, this changes the file system to
> always use the unsigned UTC interpretation, reading back times
> between
> 1970 and 2106.
> 

The trouble with HFS and HFS+ that the specification [1] declares this:

"HFS Plus stores dates in several data structures, including the volume
header and catalog records. These dates are stored in unsigned 32-bit
integers (UInt32) containing the number of seconds since midnight,
January 1, 1904, GMT. This is slightly different from HFS, where the
value represents local time. The maximum representable date is February
6, 2040 at 06:28:15 GMT."

So, I am not sure that we are able to support later dates because such
timestamps cannot be stored on HFS/HFS+ volumes and will be
incompatible with Mac OS X. Also, I am not sure that anybody will use
HFS/HFS+ after 2040.

Thanks,
Vyacheslav Dubeyko.

[1] https://developer.apple.com/library/archive/technotes/tn/tn1150.html


> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  fs/hfs/hfs_fs.h | 6 ++++--
>  fs/hfs/inode.c  | 4 ++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
> index 6d0783e2e276..ff432931a5b1 100644
> --- a/fs/hfs/hfs_fs.h
> +++ b/fs/hfs/hfs_fs.h
> @@ -245,6 +245,8 @@ extern void hfs_mark_mdb_dirty(struct super_block
> *sb);
>   *	Unix:	unsigned lil-endian since 00:00 GMT, Jan. 1,
> 1970
>   *	mac:	unsigned big-endian since 00:00 GMT, Jan. 1,
> 1904
>   *
> + * We treat all timestamps before 1970 as times after 2038, so this
> + * actually works until year 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)
> @@ -252,9 +254,9 @@ extern void hfs_mark_mdb_dirty(struct super_block
> *sb);
>  #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_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(get_seconds())
> +#define hfs_mtime()		__hfs_u_to_mtime(ktime_get_real_s
> econds())
>  
>  static inline const char *hfs_mdb_name(struct super_block *sb)
>  {
> diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
> index 2a16111d312f..b3309b83371a 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_utim
> e(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_utim
> e(rec->dir.MdDat));
> +				hfs_m_to_utime(rec->dir.MdDat);
>  		inode->i_op = &hfs_dir_inode_operations;
>  		inode->i_fop = &hfs_dir_operations;
>  		break;