Index: sys/kern/vfs_syscalls.c
===================================================================
--- sys/kern/vfs_syscalls.c	(revision 199016)
+++ sys/kern/vfs_syscalls.c	(working copy)
@@ -3587,8 +3587,12 @@
 	    AUDITVNODE1, pathseg, old, oldfd, td);
 #endif
 
-	if ((error = namei(&fromnd)) != 0)
+	if ((error = namei(&fromnd)) != 0) {
+		/* Translate error code for rename("/", "dir2"). */
+		if (error == EISDIR)
+			error = EINVAL;
 		return (error);
+	}
 	fvfslocked = NDHASGIANT(&fromnd);
 	tvfslocked = 0;
 #ifdef MAC
@@ -3737,8 +3741,12 @@
 	NDINIT_AT(&nd, CREATE, LOCKPARENT | SAVENAME | MPSAFE | AUDITVNODE1,
 	    segflg, path, fd, td);
 	nd.ni_cnd.cn_flags |= WILLBEDIR;
-	if ((error = namei(&nd)) != 0)
+	if ((error = namei(&nd)) != 0) {
+		/* Translate error code for mkdir("/"). */
+		if (error == EISDIR)
+			error = EEXIST;
 		return (error);
+	}
 	vfslocked = NDHASGIANT(&nd);
 	vp = nd.ni_vp;
 	if (vp != NULL) {
@@ -3825,10 +3833,15 @@
 	bwillwrite();
 	NDINIT_AT(&nd, DELETE, LOCKPARENT | LOCKLEAF | MPSAFE | AUDITVNODE1,
 	    pathseg, path, fd, td);
-	if ((error = namei(&nd)) != 0)
+	if ((error = namei(&nd)) != 0) {
+		/* Translate error code for rmdir("/"). */
+		if (error == EISDIR)
+			error = EBUSY;
 		return (error);
+	}
 	vfslocked = NDHASGIANT(&nd);
 	vp = nd.ni_vp;
+	/* XXX namei() takes care of this case. */
 	if (vp->v_type != VDIR) {
 		error = ENOTDIR;
 		goto out;
@@ -3841,6 +3854,7 @@
 		goto out;
 	}
 	/*
+	 * XXX namei() takes care of this case.
 	 * The root of a mounted filesystem cannot be deleted.
 	 */
 	if (vp->v_vflag & VV_ROOT) {