fellow_disk_obj: Tighten assertions on alloc.ptr cast

src/fellow_cache.c

@@ -594,7 +594,7 @@ struct fellow_disk_obj {
 
 // shaved off one pointer...
 #define FCO_FCS(fco)	(&(fco)->fdo_fcs)
-#define FCO_FDO(fco)	(void*)(fco)->fdo_fcs.alloc.ptr
+#define FCO_FDO(fco)	fellow_disk_obj(FCO_FCS(fco))
 #define FCO_REFCNT(fco) (fco)->fdo_fcs.refcnt
 #define FCO_STATE(fco)	(fco)->fdo_fcs.state
 
@@ -1018,11 +1018,12 @@ fellow_busy_io_submit(struct fellow_busy_io *fbio)
 		return (FC_ERRSTR("disk object wrong " x));	\
 	} while(0)
 
-static struct fellow_disk_obj *
+static inline struct fellow_disk_obj *
 fellow_disk_obj(const struct fellow_cache_seg *fcs)
 {
 	AN(fcs);
 	AN(fcs->alloc.ptr);
+	assert(FCOS_HIGH(fcs->state) == FCO_HIGH);
 	return (fcs->alloc.ptr);
 }
 
@@ -2167,7 +2168,7 @@ fellow_busy_obj_alloc(struct fellow_cache *fc,
 	fbo->segdskdowry = dskdowry;
 
 	// disk object in memory
-	fdo = fcs->alloc.ptr;
+	fdo = fellow_disk_obj(fcs);
 	memset(fdo, 0, fcs->alloc.size);
 	fdo->magic = FELLOW_DISK_OBJ_MAGIC;
 	fdo->version = 1;