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

native/src/init/mount.cpp

@@ -214,8 +214,6 @@ success:
 }
 
 bool LegacySARInit::mount_system_root() {
-    backup_files();
-
     LOGD("Mounting system_root\n");
 
     // there's no /dev in stub cpio
@@ -296,11 +294,19 @@ void BaseInit::exec_init() {
     exit(1);
 }
 
+void BaseInit::prepare_data() {
+    LOGD("Setup data tmp\n");
+    xmkdir("/data", 0755);
+    xmount("tmpfs", "/data", "tmpfs", 0, "mode=755");
+
+    cp_afc("/init", "/data/magiskinit");
+    cp_afc("/.backup", "/data/.backup");
+    cp_afc("/overlay.d", "/data/overlay.d");
+}
+
 void MagiskInit::setup_tmp(const char *path) {
     LOGD("Setup Magisk tmp at %s\n", path);
-    xmount("tmpfs", path, "tmpfs", 0, "mode=755");
+    chdir("/data");
-
-    chdir(path);
 
     xmkdir(INTLROOT, 0755);
     xmkdir(MIRRDIR, 0);
@@ -308,14 +314,15 @@ void MagiskInit::setup_tmp(const char *path) {
 
     mount_rules_dir();
 
-    int fd = xopen(INTLROOT "/config", O_WRONLY | O_CREAT, 0);
+    cp_afc(".backup/.magisk", INTLROOT "/config");
-    xwrite(fd, magisk_cfg.buf, magisk_cfg.sz);
+    rm_rf(".backup");
-    close(fd);
 
     // Create applet symlinks
     for (int i = 0; applet_names[i]; ++i)
         xsymlink("./magisk", applet_names[i]);
     xsymlink("./magiskpolicy", "supolicy");
 
+    xmount(".", path, nullptr, MS_BIND, nullptr);
+
     chdir("/");
 }

native/src/init/rootdir.cpp

@@ -130,19 +130,6 @@ static void magic_mount(const string &sdir, const string &ddir = "") {
     }
 }
 
-void SARBase::backup_files() {
-    if (access("/overlay.d", F_OK) == 0)
-        backup_folder("/overlay.d", overlays);
-    else if (access("/data/overlay.d", F_OK) == 0)
-        backup_folder("/data/overlay.d", overlays);
-
-    self = mmap_data("/proc/self/exe");
-    if (access("/.backup/.magisk", R_OK) == 0)
-        magisk_cfg = mmap_data("/.backup/.magisk");
-    else if (access("/data/.backup/.magisk", R_OK) == 0)
-        magisk_cfg = mmap_data("/data/.backup/.magisk");
-}
-
 static void patch_socket_name(const char *path) {
     static char rstr[16] = { 0 };
     if (rstr[0] == '\0')
@@ -181,7 +168,9 @@ static void extract_files(bool sbin) {
 #define ROOTMIR     MIRRDIR "/system_root"
 #define NEW_INITRC  "/system/etc/init/hw/init.rc"
 
-void SARBase::patch_ro_root() {
+void MagiskInit::patch_ro_root() {
+    mount_list.emplace_back("/data");
+
     string tmp_dir;
 
     if (access("/sbin", F_OK) == 0) {
@@ -205,7 +194,7 @@ void SARBase::patch_ro_root() {
     if (tmp_dir == "/sbin")
         recreate_sbin(ROOTMIR "/sbin", true);
 
-    xmkdir(ROOTOVL, 0);
+    xrename("overlay.d", ROOTOVL);
 
 #if ENABLE_AVD_HACK
     // Handle avd hack
@@ -222,9 +211,6 @@ void SARBase::patch_ro_root() {
     }
 #endif
 
-    // Handle overlay.d
-    restore_folder(ROOTOVL, overlays);
-    overlays.clear();
     load_overlay_rc(ROOTOVL);
     if (access(ROOTOVL "/sbin", F_OK) == 0) {
         // Move files in overlay.d/sbin into tmp_dir
@@ -260,9 +246,7 @@ void SARBase::patch_ro_root() {
 }
 
 void RootFSInit::prepare() {
-    self = mmap_data("/init");
+    prepare_data();
-    magisk_cfg = mmap_data("/.backup/.magisk");
-
     LOGD("Restoring /init\n");
     rename(backup_init(), "/init");
 }
@@ -270,6 +254,7 @@ void RootFSInit::prepare() {
 #define PRE_TMPDIR "/magisk-tmp"
 
 void MagiskInit::patch_rw_root() {
+    mount_list.emplace_back("/data");
     // Create hardlink mirror of /sbin to /root
     mkdir("/root", 0777);
     clone_attr("/sbin", "/root");
@@ -307,9 +292,7 @@ void MagiskInit::patch_rw_root() {
     chdir("/");
 
     // Dump magiskinit as magisk
-    int fd = xopen("/sbin/magisk", O_WRONLY | O_CREAT, 0755);
+    cp_afc(REDIR_PATH, "/sbin/magisk");
-    write(fd, self.buf, self.sz);
-    close(fd);
 }
 
 int magisk_proxy_main(int argc, char *argv[]) {

native/src/init/twostage.cpp

@@ -8,30 +8,15 @@
 
 using namespace std;
 
-#define REDIR_PATH "/data/magiskinit"
-
 void FirstStageInit::prepare() {
-    xmkdirs("/data", 0755);
+    prepare_data();
-    xmount("tmpfs", "/data", "tmpfs", 0, "mode=755");
-    cp_afc("/init" /* magiskinit */, REDIR_PATH);
-
     restore_ramdisk_init();
-
-    {
     auto init = mmap_data("/init", true);
     // Redirect original init to magiskinit
     init.patch({ make_pair(INIT_PATH, REDIR_PATH) });
-    }
-
-    // Copy files to tmpfs
-    cp_afc(".backup", "/data/.backup");
-    cp_afc("overlay.d", "/data/overlay.d");
 }
 
 void LegacySARInit::first_stage_prep() {
-    xmkdir("/data", 0755);
-    xmount("tmpfs", "/data", "tmpfs", 0, "mode=755");
-
     // Patch init binary
     int src = xopen("/init", O_RDONLY);
     int dest = xopen("/data/init", O_CREAT | O_WRONLY, 0);
@@ -43,29 +28,11 @@ void LegacySARInit::first_stage_prep() {
         close(dest);
     }
     xmount("/data/init", "/init", nullptr, MS_BIND, nullptr);
-
-    // Replace redirect init with magiskinit
-    dest = xopen(REDIR_PATH, O_CREAT | O_WRONLY, 0);
-    write(dest, self.buf, self.sz);
-    fclone_attr(src, dest);
-    close(src);
-    close(dest);
-
-    // Copy files to tmpfs
-    xmkdir("/data/.backup", 0);
-    xmkdir("/data/overlay.d", 0);
-    restore_folder("/data/overlay.d", overlays);
-    int cfg = xopen("/data/.backup/.magisk", O_WRONLY | O_CREAT, 0);
-    xwrite(cfg, magisk_cfg.buf, magisk_cfg.sz);
-    close(cfg);
 }
 
 bool SecondStageInit::prepare() {
-    backup_files();
-
     umount2("/init", MNT_DETACH);
     umount2("/proc/self/exe", MNT_DETACH);
-    umount2("/data", MNT_DETACH);
 
     // Make sure init dmesg logs won't get messed up
     argv[0] = (char *) INIT_PATH;