Skip loading Magisk when detecting DSU

Fix #4402

Co-authored-by: topjohnwu <topjohnwu@gmail.com>

native/jni/init/init.hpp

@@ -38,6 +38,7 @@ extern std::vector<std::string> mount_list;
 
 bool unxz(int fd, const uint8_t *buf, size_t size);
 void load_kernel_info(BootConfig *config);
+bool is_dsu();
 bool check_two_stage();
 void setup_klog();
 const char *backup_init();

native/jni/init/mount.cpp

@@ -93,7 +93,7 @@ static int64_t setup_block(bool write_block) {
 }
 
 static bool is_lnk(const char *name) {
-    struct stat st;
+    struct stat st{};
     if (lstat(name, &st))
         return false;
     return S_ISLNK(st.st_mode);
@@ -196,6 +196,27 @@ static void switch_root(const string &path) {
     frm_rf(root);
 }
 
+bool is_dsu() {
+    strcpy(blk_info.partname, "metadata");
+    xmkdir("/metadata", 0755);
+    if (setup_block(true) < 0 ||
+        xmount(blk_info.block_dev, "/metadata", "ext4", MS_RDONLY, nullptr)) {
+        PLOGE("Failed to mount /metadata");
+        return false;
+    } else {
+        run_finally f([]{ xumount2("/metadata", MNT_DETACH); });
+        constexpr auto dsu_status = "/metadata/gsi/dsu/install_status";
+        if (xaccess(dsu_status, F_OK) == 0) {
+            char status[PATH_MAX] = {0};
+            auto fp = xopen_file(dsu_status, "r");
+            fgets(status, sizeof(status), fp.get());
+            if (status == "ok"sv || status == "0"sv)
+                return true;
+        }
+    }
+    return false;
+}
+
 void MagiskInit::mount_rules_dir(const char *dev_base, const char *mnt_base) {
     char path[128];
     xrealpath(dev_base, blk_info.block_dev);

native/jni/init/twostage.cpp

@@ -63,6 +63,12 @@ static bool read_fstab_file(const char *fstab_file, vector<fstab_entry> &fstab)
 extern uint32_t patch_verity(void *buf, uint32_t size);
 
 void FirstStageInit::prepare() {
+    if (is_dsu()) {
+        rename(backup_init(), "/init");
+        LOGI("Skip loading Magisk because of DSU\n");
+        return;
+    }
+
     run_finally finally([]{ chdir("/"); });
     if (config->force_normal_boot) {
         xmkdirs(FSR "/system/bin", 0755);