restore: Tune up _once stuff

Having ppreh_heads we can simplify the _once helper
by re-using the .next field.
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/crtools.h

@@ -29,11 +29,16 @@ extern int cr_dedup(void);
 extern int check_add_feature(char *arg);
 extern void pr_check_features(const char *offset, const char *sep, int width);
 
-#define add_post_prepare_cb_once(phead) do {		\
-		static int __cb_called = 0;		\
-		if (!__cb_called)			\
-			add_post_prepare_cb(phead);	\
-		__cb_called = 1;			\
+#define PPREP_HEAD_INACTIVE	((struct pprep_head *)-1)
+
+#define add_post_prepare_cb_once(phead) do {		 \
+		if ((phead)->next == PPREP_HEAD_INACTIVE)\
+			add_post_prepare_cb(phead);	 \
 	} while (0)
 
+#define MAKE_PPREP_HEAD(name) struct pprep_head name = {	\
+			.next = PPREP_HEAD_INACTIVE,		\
+			.actor = name##_cb,			\
+	}
+
 #endif /* __CR_CRTOOLS_H__ */

criu/pipes.c

@@ -141,9 +141,7 @@ static int mark_pipe_master_cb(struct pprep_head *ph)
 	return 0;
 }
 
-static struct pprep_head mark_pipe_master = {
-	.actor = mark_pipe_master_cb,
-};
+static MAKE_PPREP_HEAD(mark_pipe_master);
 
 static struct pipe_data_rst *pd_hash_pipes[PIPE_DATA_HASH_SIZE];
 

criu/sk-unix.c

@@ -1360,9 +1360,7 @@ static void unlink_stale(struct unix_sk_info *ui)
 }
 
 static int resolve_unix_peers_cb(struct pprep_head *ph);
-static struct pprep_head resolve_unix_peers = {
-	.actor = resolve_unix_peers_cb,
-};
+static MAKE_PPREP_HEAD(resolve_unix_peers);
 
 static int collect_one_unixsk(void *o, ProtobufCMessage *base, struct cr_img *i)
 {

criu/tty.c

@@ -1568,10 +1568,7 @@ static int prep_tty_restore_cb(struct pprep_head *ph)
 	return 0;
 }
 
-static struct pprep_head prep_tty_restore = {
-	.actor = prep_tty_restore_cb,,
-};
-
+static MAKE_PPREP_HEAD(prep_tty_restore);
 
 static int collect_one_tty(void *obj, ProtobufCMessage *msg, struct cr_img *i)
 {