[XFS] shrink mrlock_t

The writer field is not needed for non_DEBU builds so remove it. While
we're at i also clean up the interface for is locked asserts to go through
and xfs_iget.c helper with an interface like the xfs_ilock routines to
isolated the XFS codebase from mrlock internals. That way we can kill
mrlock_t entirely once rw_semaphores grow an islocked facility. Also
remove unused flags to the ilock family of functions.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30902a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index fb3cf11..a2c3200 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -196,14 +196,14 @@
 		break;
 	case BMAPI_WRITE:
 		xfs_iomap_enter_trace(XFS_IOMAP_WRITE_ENTER, ip, offset, count);
-		lockmode = XFS_ILOCK_EXCL|XFS_EXTSIZE_WR;
+		lockmode = XFS_ILOCK_EXCL;
 		if (flags & BMAPI_IGNSTATE)
 			bmapi_flags |= XFS_BMAPI_IGSTATE|XFS_BMAPI_ENTIRE;
 		xfs_ilock(ip, lockmode);
 		break;
 	case BMAPI_ALLOCATE:
 		xfs_iomap_enter_trace(XFS_IOMAP_ALLOC_ENTER, ip, offset, count);
-		lockmode = XFS_ILOCK_SHARED|XFS_EXTSIZE_RD;
+		lockmode = XFS_ILOCK_SHARED;
 		bmapi_flags = XFS_BMAPI_ENTIRE;
 
 		/* Attempt non-blocking lock */
@@ -624,7 +624,7 @@
 	int		prealloc, fsynced = 0;
 	int		error;
 
-	ASSERT(ismrlocked(&ip->i_lock, MR_UPDATE) != 0);
+	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
 
 	/*
 	 * Make sure that the dquots are there. This doesn't hold