On Sun, Jul 17, 2022 at 06:04:31PM +0800, Xiaole He wrote:
> The 'ctime', 'mtime', and 'atime' for inode is the type of
> 'xfs_timestamp_t', which is a 64-bit type:
>
> /* fs/xfs/libxfs/xfs_format.h begin */
> typedef __be64 xfs_timestamp_t;
> /* fs/xfs/libxfs/xfs_format.h end */
>
> When the 'bigtime' feature is disabled, this 64-bit type is splitted
> into two parts of 32-bit, one part is encoded for seconds since
> 1970-01-01 00:00:00 UTC, the other part is encoded for nanoseconds
> above the seconds, this two parts are the type of
> 'xfs_legacy_timestamp' and the min and max time value of this type are
> defined as macros 'XFS_LEGACY_TIME_MIN' and 'XFS_LEGACY_TIME_MAX':
>
> /* 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 */
>
> 'XFS_LEGACY_TIME_MIN' is the min time value of the
> 'xfs_legacy_timestamp', that is -(2^31) seconds 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 */
>
> When 'bigtime' feature is enabled, this 64-bit type becomes a 64-bit
> nanoseconds counter, with the start time value is the min time value of
> 'xfs_legacy_timestamp'(start time means the value of 64-bit nanoseconds
> counter is 0). We have already caculated the min time value of
> 'xfs_legacy_timestamp', that is 1901-12-13 20:45:52 UTC, but the comment
> for the start time value of inode with 'bigtime' feature enabled writes
> the value is 1901-12-31 20:45:52 UTC:
>
> /* fs/xfs/libxfs/xfs_format.h begin */
> /*
> * XFS Timestamps
> * ==============
> * When the bigtime feature is enabled, ondisk inode timestamps become an
> * unsigned 64-bit nanoseconds counter. This means that the bigtime inode
> * timestamp epoch is the start of the classic timestamp range, which is
> * Dec 31 20:45:52 UTC 1901. ...
> ...
> */
> /* fs/xfs/libxfs/xfs_format.h end */
>
> That is a typo, and this patch corrects the typo, from 'Dec 31' to
> 'Dec 13'.
>
> Suggested-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> Signed-off-by: Xiaole He <hexiaole@xxxxxxxxxx>
Heh, thanks for fixing the typo.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> ---
> fs/xfs/libxfs/xfs_format.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index afdfc81..b55bdfa 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -704,7 +704,7 @@ struct xfs_agfl {
> * When the bigtime feature is enabled, ondisk inode timestamps become an
> * unsigned 64-bit nanoseconds counter. This means that the bigtime inode
> * timestamp epoch is the start of the classic timestamp range, which is
> - * Dec 31 20:45:52 UTC 1901. Because the epochs are not the same, callers
> + * Dec 13 20:45:52 UTC 1901. Because the epochs are not the same, callers
> * /must/ use the bigtime conversion functions when encoding and decoding raw
> * timestamps.
> */
> --
> 1.8.3.1
>
