Changes of root storage space unmounting time on Zygote Process

Zygote process forks every child process for launch the SystemServer and other
applications. When child process is forked, unmount storage inherited
from Zygote process is executed before it gains its own root storage
space.
If Zygote have no storage spaces, unmount operations not needed to
get relevant permission storage space.
Thus unmount is executed only once shortly before the SystemServer is forked.
And the child processes do not unmount its inherited root storage space.

Change-Id: I311ca7ea2c93085f42579f8cf8bdc7ef1d570a04

3 files changed, 22 insertions, 4 deletions

diff --git a/core/java/com/android/internal/os/Zygote.java b/core/java/com/android/internal/os/Zygote.java
index 919254a36a76..66cc97598ae8 100644
--- a/core/java/com/android/internal/os/Zygote.java
+++ b/core/java/com/android/internal/os/Zygote.java
@@ -149,6 +149,12 @@ public final class Zygote {
     native private static int nativeForkSystemServer(int uid, int gid, int[] gids, int debugFlags,
             int[][] rlimits, long permittedCapabilities, long effectiveCapabilities);
 
+    /**
+     * Zygote unmount storage space on initializing.
+     * This method is called once.
+     */
+    native protected static void nativeUnmountStorageOnInit();
+
     private static void callPostForkChildHooks(int debugFlags, boolean isSystemServer,
             String instructionSet) {
         VM_HOOKS.postForkChild(debugFlags, isSystemServer, instructionSet);
diff --git a/core/java/com/android/internal/os/ZygoteInit.java b/core/java/com/android/internal/os/ZygoteInit.java
index 3abea26ab42b..b658f87a9689 100644
--- a/core/java/com/android/internal/os/ZygoteInit.java
+++ b/core/java/com/android/internal/os/ZygoteInit.java
@@ -643,6 +643,9 @@ public class ZygoteInit {
             // Zygote.
             Trace.setTracingEnabled(false);
 
+            // Zygote process unmounts root storage spaces.
+            Zygote.nativeUnmountStorageOnInit();
+
             if (startSystemServer) {
                 startSystemServer(abiList, socketName);
             }
diff --git a/core/jni/com_android_internal_os_Zygote.cpp b/core/jni/com_android_internal_os_Zygote.cpp
index 612f4dfd1505..3f4b2a61321b 100644
--- a/core/jni/com_android_internal_os_Zygote.cpp
+++ b/core/jni/com_android_internal_os_Zygote.cpp
@@ -302,9 +302,6 @@ static bool MountEmulatedStorage(uid_t uid, jint mount_mode,
         return false;
     }
 
-    // Unmount storage provided by root namespace and mount requested view
-    UnmountTree("/storage");
-
     String8 storageSource;
     if (mount_mode == MOUNT_EXTERNAL_DEFAULT) {
         storageSource = "/mnt/runtime/default";
@@ -667,12 +664,24 @@ static jint com_android_internal_os_Zygote_nativeForkSystemServer(
   return pid;
 }
 
+static void com_android_internal_os_Zygote_nativeUnmountStorageOnInit(JNIEnv* env, jclass) {
+    // Zygote process unmount root storage space initially before every child processes are forked.
+    // Every forked child processes (include SystemServer) only mount their own root storage space
+    // And no need unmount storage operation in MountEmulatedStorage method.
+    // Zygote process does not utilize root storage spaces and unshared its mount namespace from the ART.
+
+    UnmountTree("/storage");
+    return;
+}
+
 static const JNINativeMethod gMethods[] = {
     { "nativeForkAndSpecialize",
       "(II[II[[IILjava/lang/String;Ljava/lang/String;[ILjava/lang/String;Ljava/lang/String;)I",
       (void *) com_android_internal_os_Zygote_nativeForkAndSpecialize },
     { "nativeForkSystemServer", "(II[II[[IJJ)I",
-      (void *) com_android_internal_os_Zygote_nativeForkSystemServer }
+      (void *) com_android_internal_os_Zygote_nativeForkSystemServer },
+    { "nativeUnmountStorageOnInit", "()V",
+      (void *) com_android_internal_os_Zygote_nativeUnmountStorageOnInit }
 };
 
 int register_com_android_internal_os_Zygote(JNIEnv* env) {