Re: [PATCH 13/18] xfs: use a union for i_cowextsize and i_flushiter

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Mar 24, 2021 at 03:21:24PM +0100, Christoph Hellwig wrote:
> The i_cowextsize field is only used for v3 inodes, and the i_flushiter
> field is only used for v1/v2 inodes.  Use a union to pack the inode a
> littler better after adding a few missing guards around their usage.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Yes, that's a nice compression opportunity.
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/libxfs/xfs_inode_buf.c | 3 ++-
>  fs/xfs/xfs_inode.c            | 6 ++++--
>  fs/xfs/xfs_inode.h            | 7 +++++--
>  fs/xfs/xfs_ioctl.c            | 6 +++++-
>  4 files changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index d090274fb8a152..96db2649f6b2fe 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -193,7 +193,8 @@ xfs_inode_from_disk(
>  	 * inode. If the inode is unused, mode is zero and we shouldn't mess
>  	 * with the uninitialized part of it.
>  	 */
> -	ip->i_flushiter = be16_to_cpu(from->di_flushiter);
> +	if (!xfs_sb_version_has_v3inode(&ip->i_mount->m_sb))
> +		ip->i_flushiter = be16_to_cpu(from->di_flushiter);
>  	inode->i_generation = be32_to_cpu(from->di_gen);
>  	inode->i_mode = be16_to_cpu(from->di_mode);
>  	if (!inode->i_mode)
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index e951ea48b3a276..b4b6fddccd1ca0 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -3459,8 +3459,10 @@ xfs_iflush(
>  	xfs_inode_to_disk(ip, dip, iip->ili_item.li_lsn);
>  
>  	/* Wrap, we never let the log put out DI_MAX_FLUSH */
> -	if (ip->i_flushiter == DI_MAX_FLUSH)
> -		ip->i_flushiter = 0;
> +	if (!xfs_sb_version_has_v3inode(&mp->m_sb)) {
> +		if (ip->i_flushiter == DI_MAX_FLUSH)
> +			ip->i_flushiter = 0;
> +	}
>  
>  	xfs_iflush_fork(ip, dip, iip, XFS_DATA_FORK);
>  	if (XFS_IFORK_Q(ip))
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 6246ee8a4359ab..7ba0ffa50ede20 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -58,8 +58,11 @@ typedef struct xfs_inode {
>  	xfs_rfsblock_t		i_nblocks;	/* # of direct & btree blocks */
>  	uint32_t		i_projid;	/* owner's project id */
>  	xfs_extlen_t		i_extsize;	/* basic/minimum extent size */
> -	xfs_extlen_t		i_cowextsize;	/* basic cow extent size */
> -	uint16_t		i_flushiter;	/* incremented on flush */
> +	/* cowextsize is only used for v3 inodes, flushiter for v1/2 */
> +	union {
> +		xfs_extlen_t	i_cowextsize;	/* basic cow extent size */
> +		uint16_t	i_flushiter;	/* incremented on flush */
> +	};
>  
>  	struct xfs_icdinode	i_d;		/* most of ondisk inode */
>  
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index e45bce9b11082c..3405a5f5bacfda 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1121,7 +1121,11 @@ xfs_fill_fsxattr(
>  
>  	simple_fill_fsxattr(fa, xfs_ip2xflags(ip));
>  	fa->fsx_extsize = ip->i_extsize << ip->i_mount->m_sb.sb_blocklog;
> -	fa->fsx_cowextsize = ip->i_cowextsize << ip->i_mount->m_sb.sb_blocklog;
> +	if (xfs_sb_version_has_v3inode(&ip->i_mount->m_sb) &&
> +	    (ip->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE)) {
> +		fa->fsx_cowextsize =
> +			ip->i_cowextsize << ip->i_mount->m_sb.sb_blocklog;
> +	}
>  	fa->fsx_projid = ip->i_projid;
>  	if (ifp && (ifp->if_flags & XFS_IFEXTENTS))
>  		fa->fsx_nextents = xfs_iext_count(ifp);
> -- 
> 2.30.1
>