xfs: use a union for i_cowextsize and i_flushiter

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: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDarrick J. Wong <djwong@kernel.org>
Signed-off-by: NDarrick J. Wong <djwong@kernel.org>

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)

fs/xfs/xfs_inode.c

@@ -3483,8 +3483,10 @@ 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))

fs/xfs/xfs_inode.h

@@ -58,8 +58,11 @@ typedef struct xfs_inode {
 	xfs_rfsblock_t		i_nblocks;	/* # of direct & btree blocks */
 	prid_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 */
 

fs/xfs/xfs_ioctl.c

@@ -1123,7 +1123,8 @@ xfs_fill_fsxattr(
 	simple_fill_fsxattr(fa, xfs_ip2xflags(ip));
 
 	fa->fsx_extsize = XFS_FSB_TO_B(mp, ip->i_extsize);
-	fa->fsx_cowextsize = XFS_FSB_TO_B(mp, ip->i_cowextsize);
+	if (ip->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE)
+		fa->fsx_cowextsize = XFS_FSB_TO_B(mp, ip->i_cowextsize);
 	fa->fsx_projid = ip->i_projid;
 	if (ifp && (ifp->if_flags & XFS_IFEXTENTS))
 		fa->fsx_nextents = xfs_iext_count(ifp);
@@ -1523,11 +1524,13 @@ xfs_ioctl_setattr(
 		ip->i_extsize = XFS_B_TO_FSB(mp, fa->fsx_extsize);
 	else
 		ip->i_extsize = 0;
-	if (xfs_sb_version_has_v3inode(&mp->m_sb) &&
-	    (ip->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE))
-		ip->i_cowextsize = XFS_B_TO_FSB(mp, fa->fsx_cowextsize);
-	else
-		ip->i_cowextsize = 0;
+
+	if (xfs_sb_version_has_v3inode(&mp->m_sb)) {
+		if (ip->i_d.di_flags2 & XFS_DIFLAG2_COWEXTSIZE)
+			ip->i_cowextsize = XFS_B_TO_FSB(mp, fa->fsx_cowextsize);
+		else
+			ip->i_cowextsize = 0;
+	}
 
 	error = xfs_trans_commit(tp);