staging/lustre/llite: Anonymous dentry incorrectly identified as root

When exporting Lustre via NFS on SLES11SP2, this check incorrectly identifies
anonymous dentries as root dentries.  This is due to a change in SLES11SP2
which makes the d_name.name for anonymous dentries the same as that for root
dentries.  (Details in LU-3484.)

This changes the check to directly compare the value of the dentry pointer
to the root dentry pointer found in the superblock, rather than using the name.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3484
Lustre-change: http://review.whamcloud.com/6726Signed-off-by: NPatrick Farrell <paf@cray.com>
Reviewed-by: NBob Glossman <bob.glossman@intel.com>
Reviewed-by: NAndreas Dilger <andreas.dilger@intel.com>
Reviewed-by: NPeng Tao <bergwolf@gmail.com>
Reviewed-by: NJames Simmons <uja.ornl@gmail.com>
Reviewed-by: NAlexey Shvetsov <alexxy@gentoo.org>
Signed-off-by: NPeng Tao <tao.peng@emc.com>
Signed-off-by: NAndreas Dilger <andreas.dilger@intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/llite/dcache.c

@@ -295,9 +295,10 @@ void ll_invalidate_aliases(struct inode *inode)
 		       dentry->d_name.name, dentry, dentry->d_parent,
 		       dentry->d_inode, dentry->d_flags);
 
-		if (dentry->d_name.len == 1 && dentry->d_name.name[0] == '/') {
-			CERROR("called on root (?) dentry=%p, inode=%p "
-			       "ino=%lu\n", dentry, inode, inode->i_ino);
+		if (unlikely(dentry == dentry->d_sb->s_root)) {
+			CERROR("%s: called on root dentry=%p, fid="DFID"\n",
+			       ll_get_fsname(dentry->d_sb, NULL, 0),
+			       dentry, PFID(ll_inode2fid(inode)));
 			lustre_dump_dentry(dentry, 1);
 			dump_stack();
 		}