irmap: Try to load irmap cache from parent as well

If we make workdir coincide with images dir, the irmap
cache will be put in parent images for subsequent dump-s.
Try to load it from there.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

irmap.c

@@ -347,20 +347,43 @@ static int irmap_cache_one(IrmapCacheEntry *ie)
 	return 0;
 }
 
-int irmap_load_cache(void)
+static int open_irmap_cache(int *fd)
 {
-	int fd, ret;
+	int dir = AT_FDCWD;
 
-	fd = open_image_at(AT_FDCWD, CR_FD_IRMAP_CACHE, O_RSTR);
-	if (fd < 0) {
-		if (errno == ENOENT) {
-			pr_info("No irmap cache\n");
-			return 0;
-		}
+	pr_info("Searching irmap cache in work dir\n");
+in:
+	*fd = open_image_at(dir, CR_FD_IRMAP_CACHE, O_RSTR);
+	if (dir != AT_FDCWD)
+		close(dir);
 
-		return -1;
+	if (*fd >= 0) {
+		pr_info("... done\n");
+		return 1;
 	}
 
+	if (errno == ENOENT && dir == AT_FDCWD) {
+		pr_info("Searching irmap cache in parent\n");
+		dir = openat(get_service_fd(IMG_FD_OFF), CR_PARENT_LINK, O_RDONLY);
+		if (dir >= 0)
+			goto in;
+	}
+
+	if (errno != ENOENT)
+		return -1;
+
+	pr_info("No irmap cache\n");
+	return 0;
+}
+
+int irmap_load_cache(void)
+{
+	int fd, ret;
+
+	ret = open_irmap_cache(&fd);
+	if (ret <= 0)
+		return ret;
+
 	pr_info("Loading irmap cache\n");
 	while (1) {
 		IrmapCacheEntry *ic;
@@ -378,5 +401,4 @@ int irmap_load_cache(void)
 
 	close(fd);
 	return ret;
-
 }