Re: [PATCH 01/11] xfs: explicitly define inode timestamp range

[Dave Chinner <david@fromorbit.com>]

On Thu, Aug 20, 2020 at 07:11:34PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Formally define the inode timestamp ranges that existing filesystems
> support, and switch the vfs timetamp ranges to use it.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_format.h |   19 +++++++++++++++++++
>  fs/xfs/xfs_ondisk.h        |   12 ++++++++++++
>  fs/xfs/xfs_super.c         |    5 +++--
>  3 files changed, 34 insertions(+), 2 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index be86fa1a5556..b1b8a5c05cea 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -849,11 +849,30 @@ struct xfs_agfl {
>  	    ASSERT(xfs_daddr_to_agno(mp, d) == \
>  		   xfs_daddr_to_agno(mp, (d) + (len) - 1)))
>  
> +/*
> + * XFS Timestamps
> + * ==============
> + *
> + * Inode timestamps consist of signed 32-bit counters for seconds and
> + * nanoseconds; time zero is the Unix epoch, Jan  1 00:00:00 UTC 1970.
> + */
>  typedef struct xfs_timestamp {
>  	__be32		t_sec;		/* timestamp seconds */
>  	__be32		t_nsec;		/* timestamp nanoseconds */
>  } xfs_timestamp_t;
>  
> +/*
> + * Smallest possible timestamp with traditional timestamps, which is
> + * Dec 13 20:45:52 UTC 1901.
> + */
> +#define XFS_INO_TIME_MIN	((int64_t)S32_MIN)
> +
> +/*
> + * Largest possible timestamp with traditional timestamps, which is
> + * Jan 19 03:14:07 UTC 2038.
> + */
> +#define XFS_INO_TIME_MAX	((int64_t)S32_MAX)

These are based on the Unix epoch. Can we call them something like
XFS_INO_UNIX_TIME_{MIN,MAX} to indicate what epoch they reference?

>  /*
>   * On-disk inode structure.
>   *
> diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h
> index acb9b737fe6b..48a64fa49f91 100644
> --- a/fs/xfs/xfs_ondisk.h
> +++ b/fs/xfs/xfs_ondisk.h
> @@ -15,6 +15,18 @@
>  		"XFS: offsetof(" #structname ", " #member ") is wrong, " \
>  		"expected " #off)
>  
> +#define XFS_CHECK_VALUE(value, expected) \
> +	BUILD_BUG_ON_MSG((value) != (expected), \
> +		"XFS: value of " #value " is wrong, expected " #expected)
> +
> +static inline void __init
> +xfs_check_limits(void)
> +{
> +	/* make sure timestamp limits are correct */
> +	XFS_CHECK_VALUE(XFS_INO_TIME_MIN,			-2147483648LL);
> +	XFS_CHECK_VALUE(XFS_INO_TIME_MAX,			2147483647LL);
> +}

Not sure this really gains us anything? All it does is check that
S32_MIN/S32_MAX haven't changed value....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com