Re: [PATCH 08/11] xfs: widen ondisk inode timestamps to deal with y2038+

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Aug 27, 2020 at 07:58:16AM +0100, Christoph Hellwig wrote:
> > -	tv.tv_sec = (int64_t)t >> 32;
> > -	tv.tv_nsec = (int32_t)(t & 0xffffffff);
> > +	if (xfs_dinode_has_bigtime(dip)) {
> > +		s = xfs_bigtime_to_unix(div_u64_rem(t, NSEC_PER_SEC, &n));
> > +	} else {
> > +		s = (int64_t)t >> 32;
> > +		n = (int32_t)(t & 0xffffffff);
> 
> Move this branche into a xfs_legacytime_to_unix helper just to be
> symmetric?
> 
> This also made me think of the encoding:  another sensible option
> would be to always read the time stamps as two 32-bit values using the
> struct type, and just add them up for the bigtime case.
> 
> > +	if (xfs_inode_has_bigtime(ip))
> > +		t = xfs_inode_encode_bigtime(tv);
> > +	else
> > +		t = ((int64_t)tv.tv_sec << 32) | (tv.tv_nsec & 0xffffffff);
> > +
> 
> Same here.

<shrug> I think I'd rather just keep the legacy struct xfs_{ic,}timestamp,
change the xfs_dinode/xfs_log_dinode structs to have a be64/u64
timestamp, and cast pointers as needed to support the legacy formats.

> > @@ -305,9 +320,9 @@ xfs_inode_to_disk(
> >  	to->di_projid_hi = cpu_to_be16(from->di_projid >> 16);
> >  
> >  	memset(to->di_pad, 0, sizeof(to->di_pad));
> > -	to->di_atime = xfs_inode_to_disk_ts(inode->i_atime);
> > -	to->di_mtime = xfs_inode_to_disk_ts(inode->i_mtime);
> > -	to->di_ctime = xfs_inode_to_disk_ts(inode->i_ctime);
> > +	to->di_atime = xfs_inode_to_disk_ts(ip, inode->i_atime);
> > +	to->di_mtime = xfs_inode_to_disk_ts(ip, inode->i_mtime);
> > +	to->di_ctime = xfs_inode_to_disk_ts(ip, inode->i_ctime);
> >  	to->di_nlink = cpu_to_be32(inode->i_nlink);
> >  	to->di_gen = cpu_to_be32(inode->i_generation);
> >  	to->di_mode = cpu_to_be16(inode->i_mode);
> > @@ -326,7 +341,7 @@ xfs_inode_to_disk(
> >  	if (xfs_sb_version_has_v3inode(&ip->i_mount->m_sb)) {
> >  		to->di_version = 3;
> >  		to->di_changecount = cpu_to_be64(inode_peek_iversion(inode));
> > -		to->di_crtime = xfs_inode_to_disk_ts(from->di_crtime);
> > +		to->di_crtime = xfs_inode_to_disk_ts(ip, from->di_crtime);
> >  		to->di_flags2 = cpu_to_be64(from->di_flags2);
> >  		to->di_cowextsize = cpu_to_be32(from->di_cowextsize);
> >  		to->di_ino = cpu_to_be64(ip->i_ino);
> > @@ -546,6 +561,11 @@ xfs_dinode_verify(
> >  	if (fa)
> >  		return fa;
> >  
> > +	/* bigtime iflag can only happen on bigtime filesystems */
> > +	if (xfs_dinode_has_bigtime(dip) &&
> > +	    !xfs_sb_version_hasbigtime(&mp->m_sb))
> > +		return __this_address;
> > +
> >  	return NULL;
> >  }
> >  
> > diff --git a/fs/xfs/libxfs/xfs_inode_buf.h b/fs/xfs/libxfs/xfs_inode_buf.h
> > index 3060ecd24a2e..e05bfe52fd8f 100644
> > --- a/fs/xfs/libxfs/xfs_inode_buf.h
> > +++ b/fs/xfs/libxfs/xfs_inode_buf.h
> > @@ -32,6 +32,11 @@ struct xfs_icdinode {
> >  	struct timespec64 di_crtime;	/* time created */
> >  };
> >  
> > +static inline bool xfs_icdinode_has_bigtime(const struct xfs_icdinode *icd)
> > +{
> > +	return icd->di_flags2 & XFS_DIFLAG2_BIGTIME;
> > +}
> > +
> >  /*
> >   * Inode location information.  Stored in the inode and passed to
> >   * xfs_imap_to_bp() to get a buffer and dinode for a given inode.
> > @@ -58,6 +63,14 @@ xfs_failaddr_t xfs_inode_validate_cowextsize(struct xfs_mount *mp,
> >  		uint32_t cowextsize, uint16_t mode, uint16_t flags,
> >  		uint64_t flags2);
> >  
> > -struct timespec64 xfs_inode_from_disk_ts(const xfs_timestamp_t ts);
> > +static inline uint64_t xfs_inode_encode_bigtime(struct timespec64 tv)
> > +{
> > +	uint64_t	t = xfs_unix_to_bigtime(tv.tv_sec) * NSEC_PER_SEC;
> > +
> > +	return t + tv.tv_nsec;
> 
> Why not:
> 
> 	return xfs_unix_to_bigtime(tv.tv_sec) * NSEC_PER_SEC + tv.tv_nsec;
> 
> ?

Heh, ok, will do.

> > +static inline bool xfs_inode_want_bigtime_upgrade(struct xfs_inode *ip)
> > +{
> > +	return xfs_sb_version_hasbigtime(&ip->i_mount->m_sb) &&
> > +	       !xfs_inode_has_bigtime(ip);
> > +}
> > +
> >  /*
> >   * This is called to mark the fields indicated in fieldmask as needing to be
> >   * logged when the transaction is committed.  The inode must already be
> > @@ -131,6 +137,16 @@ xfs_trans_log_inode(
> >  			iversion_flags = XFS_ILOG_CORE;
> >  	}
> >  
> > +	/*
> > +	 * If we're updating the inode core or the timestamps and it's possible
> > +	 * to upgrade this inode to bigtime format, do so now.
> > +	 */
> > +	if ((flags & (XFS_ILOG_CORE | XFS_ILOG_TIMESTAMP)) &&
> > +	    xfs_inode_want_bigtime_upgrade(ip)) {
> > +		ip->i_d.di_flags2 |= XFS_DIFLAG2_BIGTIME;
> > +		flags |= XFS_ILOG_CORE;
> > +	}
> 
> I find the way to directly set XFS_DIFLAG2_BIGTIME but using a helper
> to check it here rather confusing.
> 
> Why not:
> 
> 	if (xfs_sb_version_hasbigtime(&ip->i_mount->m_sb) &&
> 	    (flags & (XFS_ILOG_CORE | XFS_ILOG_TIMESTAMP)) &&
> 	    !(ip->i_d.di_flags2 & XFS_DIFLAG2_BIGTIME)) {
> 		ip->i_d.di_flags2 |= XFS_DIFLAG2_BIGTIME;
> 		flags |= XFS_ILOG_CORE;
> 	}
> 
> ?

The previous version had it that way; Dave asked me to make it a helper.

--D