[PATCH v2 1/2] xfsdocs: fix inode timestamps lower limit value

[PATCH v2 1/2] xfsdocs: fix inode timestamps lower limit value

[Xiaole He]

In kernel source tree 'fs/xfs/libxfs/xfs_format.h', there defined inode
timestamps as 'xfs_legacy_timestamp' if the 'bigtime' feature disabled,
and also defined the min and max time constants 'XFS_LEGACY_TIME_MIN'
and 'XFS_LEGACY_TIME_MAX' as below:

/* fs/xfs/libxfs/xfs_format.h begin */
struct xfs_legacy_timestamp {
        __be32          t_sec;          /* timestamp seconds */
        __be32          t_nsec;         /* timestamp nanoseconds */
};
 #define XFS_LEGACY_TIME_MIN     ((int64_t)S32_MIN)
 #define XFS_LEGACY_TIME_MAX     ((int64_t)S32_MAX)
/* fs/xfs/libxfs/xfs_format.h end */
/* include/linux/limits.h begin */
 #define U32_MAX         ((u32)~0U)
 #define S32_MAX         ((s32)(U32_MAX >> 1))
 #define S32_MIN         ((s32)(-S32_MAX - 1))
/* include/linux/limits.h end */

When the 't_sec' and 't_nsec' are 0, the time value it represents is
1970-01-01 00:00:00 UTC, the 'XFS_LEGACY_TIME_MIN', that is -(2^31),
represents the min second offset relative to the
1970-01-01 00:00:00 UTC, it can be converted to human-friendly time
value by 'date' command:

/* command begin */
[root@~]# date --utc -d '@0' +'%Y-%m-%d %H:%M:%S'
1970-01-01 00:00:00
[root@~]# date --utc -d "@`echo '-(2^31)'|bc`" +'%Y-%m-%d %H:%M:%S'
1901-12-13 20:45:52
[root@~]#
/* command end */

That is, the min time value is 1901-12-13 20:45:52 UTC, but the
'design/XFS_Filesystem_Structure/timestamps.asciidoc' write the min
time value as 'The smalle st date this format can represent is
20:45:52 UTC on December 31st', there should be a typo, and this patch
correct 2 places of wrong min time value, from '31st' to '13st'.

Signed-off-by: Xiaole He <hexiaole@kylinos.cn>
---
V1 -> V2: Wrap line at 72 column, add Signed-off-by, add one more 
'date' command for explanation, remove the question section.

 design/XFS_Filesystem_Structure/timestamps.asciidoc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/design/XFS_Filesystem_Structure/timestamps.asciidoc b/design/XFS_Filesystem_Structure/timestamps.asciidoc
index 08baa1e..56d4dc9 100644
--- a/design/XFS_Filesystem_Structure/timestamps.asciidoc
+++ b/design/XFS_Filesystem_Structure/timestamps.asciidoc
@@ -26,13 +26,13 @@ struct xfs_legacy_timestamp {
 };
 ----
 
-The smallest date this format can represent is 20:45:52 UTC on December 31st,
+The smallest date this format can represent is 20:45:52 UTC on December 13st,
 1901, and the largest date supported is 03:14:07 UTC on January 19, 2038.
 
 With the introduction of the bigtime feature, the format is changed to
 interpret the timestamp as a 64-bit count of nanoseconds since the smallest
 date supported by the old encoding.  This means that the smallest date
-supported is still 20:45:52 UTC on December 31st, 1901; but now the largest
+supported is still 20:45:52 UTC on December 13st, 1901; but now the largest
 date supported is 20:20:24 UTC on July 2nd, 2486.
 
 [[Quota_Timers]]
-- 
1.8.3.1

Re: [PATCH v2 1/2] xfsdocs: fix inode timestamps lower limit value

[Darrick J. Wong]

On Sun, Jul 17, 2022 at 06:07:28PM +0800, Xiaole He wrote:
> In kernel source tree 'fs/xfs/libxfs/xfs_format.h', there defined inode
> timestamps as 'xfs_legacy_timestamp' if the 'bigtime' feature disabled,
> and also defined the min and max time constants 'XFS_LEGACY_TIME_MIN'
> and 'XFS_LEGACY_TIME_MAX' as below:
> 
> /* fs/xfs/libxfs/xfs_format.h begin */
> struct xfs_legacy_timestamp {
>         __be32          t_sec;          /* timestamp seconds */
>         __be32          t_nsec;         /* timestamp nanoseconds */
> };
>  #define XFS_LEGACY_TIME_MIN     ((int64_t)S32_MIN)
>  #define XFS_LEGACY_TIME_MAX     ((int64_t)S32_MAX)
> /* fs/xfs/libxfs/xfs_format.h end */
> /* include/linux/limits.h begin */
>  #define U32_MAX         ((u32)~0U)
>  #define S32_MAX         ((s32)(U32_MAX >> 1))
>  #define S32_MIN         ((s32)(-S32_MAX - 1))
> /* include/linux/limits.h end */
> 
> When the 't_sec' and 't_nsec' are 0, the time value it represents is
> 1970-01-01 00:00:00 UTC, the 'XFS_LEGACY_TIME_MIN', that is -(2^31),
> represents the min second offset relative to the
> 1970-01-01 00:00:00 UTC, it can be converted to human-friendly time
> value by 'date' command:
> 
> /* command begin */
> [root@~]# date --utc -d '@0' +'%Y-%m-%d %H:%M:%S'
> 1970-01-01 00:00:00
> [root@~]# date --utc -d "@`echo '-(2^31)'|bc`" +'%Y-%m-%d %H:%M:%S'
> 1901-12-13 20:45:52
> [root@~]#
> /* command end */
> 
> That is, the min time value is 1901-12-13 20:45:52 UTC, but the
> 'design/XFS_Filesystem_Structure/timestamps.asciidoc' write the min
> time value as 'The smalle st date this format can represent is
> 20:45:52 UTC on December 31st', there should be a typo, and this patch
> correct 2 places of wrong min time value, from '31st' to '13st'.
> 
> Signed-off-by: Xiaole He <hexiaole@kylinos.cn>

Looks correct, will commit...
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> V1 -> V2: Wrap line at 72 column, add Signed-off-by, add one more 
> 'date' command for explanation, remove the question section.
> 
>  design/XFS_Filesystem_Structure/timestamps.asciidoc | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/design/XFS_Filesystem_Structure/timestamps.asciidoc b/design/XFS_Filesystem_Structure/timestamps.asciidoc
> index 08baa1e..56d4dc9 100644
> --- a/design/XFS_Filesystem_Structure/timestamps.asciidoc
> +++ b/design/XFS_Filesystem_Structure/timestamps.asciidoc
> @@ -26,13 +26,13 @@ struct xfs_legacy_timestamp {
>  };
>  ----
>  
> -The smallest date this format can represent is 20:45:52 UTC on December 31st,
> +The smallest date this format can represent is 20:45:52 UTC on December 13st,
>  1901, and the largest date supported is 03:14:07 UTC on January 19, 2038.
>  
>  With the introduction of the bigtime feature, the format is changed to
>  interpret the timestamp as a 64-bit count of nanoseconds since the smallest
>  date supported by the old encoding.  This means that the smallest date
> -supported is still 20:45:52 UTC on December 31st, 1901; but now the largest
> +supported is still 20:45:52 UTC on December 13st, 1901; but now the largest
>  date supported is 20:20:24 UTC on July 2nd, 2486.
>  
>  [[Quota_Timers]]
> -- 
> 1.8.3.1
>