Eliminate unnecessarily copy on magiskinit

This patch reuses the abused /data tmpfs for magisktmp

native/src/init/init.hpp

@@ -25,6 +25,7 @@ struct BootConfig {
 
 #define DEFAULT_DT_DIR "/proc/device-tree/firmware/android"
 #define INIT_PATH  "/system/bin/init"
+#define REDIR_PATH "/data/magiskinit"
 
 extern std::vector<std::string> mount_list;
 
@@ -48,6 +49,7 @@ protected:
     char **argv = nullptr;
 
     [[noreturn]] void exec_init();
+    void prepare_data();
 public:
     BaseInit(char *argv[], BootConfig *config = nullptr) : config(config), argv(argv) {}
     virtual ~BaseInit() = default;
@@ -58,8 +60,6 @@ class MagiskInit : public BaseInit {
 private:
     void mount_rules_dir();
 protected:
-    mmap_data self;
-    mmap_data magisk_cfg;
     std::string custom_rules_dir;
 
 #if ENABLE_AVD_HACK
@@ -72,16 +72,12 @@ protected:
     bool hijack_sepolicy();
     void setup_tmp(const char *path);
     void patch_rw_root();
+    void patch_ro_root();
 public:
     using BaseInit::BaseInit;
 };
 
 class SARBase : public MagiskInit {
-protected:
-    std::vector<raw_file> overlays;
-
-    void backup_files();
-    void patch_ro_root();
 public:
     using MagiskInit::MagiskInit;
 };
@@ -134,6 +130,7 @@ public:
         LOGD("%s\n", __FUNCTION__);
     };
     void start() override {
+        prepare_data();
         if (mount_system_root())
             first_stage_prep();
         else