block: try to find the root device on both / and /rom

Sometimes / is already overlay mounted, assume /rom contains the real
rootfs.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

block.c

@@ -1397,14 +1397,14 @@ static int find_block_ubi_RO(libubi_t libubi, char *name, char *part, int plen)
 }
 #endif
 
-static int find_root_dev(char *buf, int len)
+static int find_dev(const char *path, char *buf, int len)
 {
 	DIR *d;
 	dev_t root;
 	struct stat s;
 	struct dirent *e;
 
-	if (stat("/", &s))
+	if (stat(path, &s))
 		return -1;
 
 	if (!(d = opendir("/dev")))
@@ -1426,6 +1426,15 @@ static int find_root_dev(char *buf, int len)
 	return -1;
 }
 
+static int find_root_dev(char *buf, int len)
+{
+	int err = find_dev("/", buf, len);
+	if (err)
+	    err = find_dev("/rom", buf, len);
+
+	return err;
+}
+
 static int test_fs_support(const char *name)
 {
 	char line[128], *p;