[XFS] optimize XFS_IS_REALTIME_INODE w/o realtime config

Use XFS_IS_REALTIME_INODE in more places, and #define it to 0 if
CONFIG_XFS_RT is off. This should be safe because mount checks in
xfs_rtmount_init:

so if we get mounted w/o CONFIG_XFS_RT, no realtime inodes should be
encountered after that.

Defining XFS_IS_REALTIME_INODE to 0 saves a bit of stack space,
presumeably gcc can optimize around the various "if (0)" type checks:

xfs_alloc_file_space -8 xfs_bmap_adjacent -16 xfs_bmapi -8
xfs_bmap_rtalloc -16 xfs_bunmapi -28 xfs_free_file_space -64 xfs_imap +8
<-- ? hmm. xfs_iomap_write_direct -12 xfs_qm_dqusage_adjust -4
xfs_qm_vop_chown_reserve -4

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30014a

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 637a244..fde37f8 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -141,7 +141,7 @@
 		iomapp->iomap_bsize = XFS_FSB_TO_B(mp, imap->br_blockcount);
 		iomapp->iomap_flags = flags;
 
-		if (ip->i_d.di_flags & XFS_DIFLAG_REALTIME) {
+		if (XFS_IS_REALTIME_INODE(ip)) {
 			iomapp->iomap_flags |= IOMAP_REALTIME;
 			iomapp->iomap_target = mp->m_rtdev_targp;
 		} else {
@@ -298,7 +298,7 @@
 	xfs_extlen_t	align;
 	int		eof, error;
 
-	if (ip->i_d.di_flags & XFS_DIFLAG_REALTIME)
+	if (XFS_IS_REALTIME_INODE(ip))
 		;
 	/*
 	 * If mounted with the "-o swalloc" option, roundup the allocation
@@ -524,7 +524,7 @@
 	}
 
 	if (unlikely(!imap.br_startblock &&
-		     !(ip->i_d.di_flags & XFS_DIFLAG_REALTIME))) {
+		     !(XFS_IS_REALTIME_INODE(ip)))) {
 		error = xfs_cmn_err_fsblock_zero(ip, &imap);
 		goto error_out;
 	}
@@ -687,7 +687,7 @@
 	}
 
 	if (unlikely(!imap[0].br_startblock &&
-		     !(ip->i_d.di_flags & XFS_DIFLAG_REALTIME)))
+		     !(XFS_IS_REALTIME_INODE(ip))))
 		return xfs_cmn_err_fsblock_zero(ip, &imap[0]);
 
 	*ret_imap = imap[0];
@@ -932,7 +932,7 @@
 			return XFS_ERROR(error);
 
 		if (unlikely(!imap.br_startblock &&
-			     !(ip->i_d.di_flags & XFS_DIFLAG_REALTIME)))
+			     !(XFS_IS_REALTIME_INODE(ip))))
 			return xfs_cmn_err_fsblock_zero(ip, &imap);
 
 		if ((numblks_fsb = imap.br_blockcount) == 0) {