[XFS] streamline init/exit path

Currently the xfs module init/exit code is a mess. It's farmed out over a
lot of function with very little error checking. This patch makes sure we
propagate all initialization failures properly and clean up after them.
Various runtime initializations are replaced with compile-time
initializations where possible to make this easier. The exit path is
similarly consolidated.

There's now split out function to create/destroy the kmem zones and
alloc/free the trace buffers. I've also changed the ktrace allocations to
KM_MAYFAIL and handled errors resulting from that.

And yes, we really should replace the XFS_*_TRACE ifdefs with a single
XFS_TRACE..

SGI-PV: 976035

SGI-Modid: xfs-linux-melb:xfs-kern:31354a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Niv Sardi <xaiki@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_mru_cache.c b/fs/xfs/xfs_mru_cache.c
index 26d14a1..afee7eb 100644
--- a/fs/xfs/xfs_mru_cache.c
+++ b/fs/xfs/xfs_mru_cache.c
@@ -307,15 +307,18 @@
 	xfs_mru_elem_zone = kmem_zone_init(sizeof(xfs_mru_cache_elem_t),
 	                                 "xfs_mru_cache_elem");
 	if (!xfs_mru_elem_zone)
-		return ENOMEM;
+		goto out;
 
 	xfs_mru_reap_wq = create_singlethread_workqueue("xfs_mru_cache");
-	if (!xfs_mru_reap_wq) {
-		kmem_zone_destroy(xfs_mru_elem_zone);
-		return ENOMEM;
-	}
+	if (!xfs_mru_reap_wq)
+		goto out_destroy_mru_elem_zone;
 
 	return 0;
+
+ out_destroy_mru_elem_zone:
+	kmem_zone_destroy(xfs_mru_elem_zone);
+ out:
+	return -ENOMEM;
 }
 
 void