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

From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
	linux-xfs@vger.kernel.org, sandeen@sandeen.net
Subject: Re: [PATCH 01/11] xfs: explicitly define inode timestamp range
Date: Sun, 23 Aug 2020 19:34:07 -0700	[thread overview]
Message-ID: <20200824023407.GO6096@magnolia> (raw)
In-Reply-To: <20200823235429.GJ7941@dread.disaster.area>

On Mon, Aug 24, 2020 at 09:54:29AM +1000, Dave Chinner wrote:
> 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?

I'll update the comment and name to make it clear that this is the Unix
epoch we're talking about.

> >  /*
> >   * 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....

Will remove.

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com