Run prepare() for BackupSoSource to cleanup previous state

Summary:
Currently, the BackupSoSource does not clean after itself when a new version of the app is installed. That is because prepare() does not run unless there is a crash.

This diff changes that by running prepare() with special flags whenever initialising SoLoader. With the new flag, we make sure that `deleteSoFiles` runs when necessary, e.g. when deps have changed.

To differentiate between different states, we simply skip writing sos to disk and the deps state (which is empty).

Reviewed By: danjin250

Differential Revision: D60186847

fbshipit-source-id: e029b9c31ac9a677cae5e9c9d80cf8aee79da35d

Author: adicatana

java/com/facebook/soloader/BackupSoSource.java

@@ -100,7 +100,8 @@ public int loadLibrary(String soName, int loadFlags, StrictMode.ThreadPolicy thr
 
   @Override
   public void prepare(int flags) throws IOException {
-    if ((flags & SoSource.PREPARE_FLAG_SKIP_BACKUP_SO_SOURCE) != 0) {
+    if ((flags & SoSource.PREPARE_FLAG_NO_UNPACKING_BACKUP_SO_SOURCE) != 0) {
+      super.prepare(flags | SoSource.PREPARE_FLAG_NO_UNPACKING);
       return;
     }
     super.prepare(flags);

java/com/facebook/soloader/SoLoader.java

@@ -534,7 +534,7 @@ private static int makePrepareFlags() {
         prepareFlags |= SoSource.PREPARE_FLAG_DISABLE_FS_SYNC_JOB;
       }
       if ((sFlags & SOLOADER_EXPLICITLY_ENABLE_BACKUP_SOSOURCE) == 0) {
-        prepareFlags |= SoSource.PREPARE_FLAG_SKIP_BACKUP_SO_SOURCE;
+        prepareFlags |= SoSource.PREPARE_FLAG_NO_UNPACKING_BACKUP_SO_SOURCE;
       }
       return prepareFlags;
     } finally {

java/com/facebook/soloader/SoSource.java

@@ -59,7 +59,9 @@ public abstract class SoSource {
   public static final int PREPARE_FLAG_DISABLE_FS_SYNC_JOB = (1 << 2);
 
   /** Skip preparing backup so source. */
-  public static final int PREPARE_FLAG_SKIP_BACKUP_SO_SOURCE = (1 << 3);
+  public static final int PREPARE_FLAG_NO_UNPACKING_BACKUP_SO_SOURCE = (1 << 3);
+
+  public static final int PREPARE_FLAG_NO_UNPACKING = (1 << 4);
 
   /** Prepare to install this SoSource in SoLoader. */
   protected void prepare(int flags) throws IOException {

java/com/facebook/soloader/UnpackingSoSource.java

@@ -338,18 +338,23 @@ private boolean refreshLocked(final FileLocker lock, final int flags) throws IOE
     LogUtil.v(TAG, "so store dirty: regenerating");
     writeState(stateFileName, STATE_DIRTY, runFsync);
     deleteSoFiles();
-    try (Unpacker u = makeUnpacker()) {
-      u.unpack(soDirectory);
-    }
 
-    // N.B. We can afford to write the deps file without fsyncs because we've marked the DSO
-    // store STATE_DIRTY, which will cause us to ignore all intermediate state when regenerating it.
-    // That is, it's okay for the depsFile blocks to hit the disk before the actual DSO data file
-    // blocks as long as both hit the disk before we reset STATE_CLEAN.
-    final File depsFileName = new File(soDirectory, DEPS_FILE_NAME);
-    try (RandomAccessFile depsFile = new RandomAccessFile(depsFileName, "rw")) {
-      depsFile.write(recomputedDeps);
-      depsFile.setLength(depsFile.getFilePointer());
+    final boolean noUnpacking = (flags & PREPARE_FLAG_NO_UNPACKING) != 0;
+    if (!noUnpacking) {
+      try (Unpacker u = makeUnpacker()) {
+        u.unpack(soDirectory);
+      }
+
+      // N.B. We can afford to write the deps file without fsyncs because we've marked the DSO
+      // store STATE_DIRTY, which will cause us to ignore all intermediate state when regenerating
+      // it.
+      // That is, it's okay for the depsFile blocks to hit the disk before the actual DSO data file
+      // blocks as long as both hit the disk before we reset STATE_CLEAN.
+      final File depsFileName = new File(soDirectory, DEPS_FILE_NAME);
+      try (RandomAccessFile depsFile = new RandomAccessFile(depsFileName, "rw")) {
+        depsFile.write(recomputedDeps);
+        depsFile.setLength(depsFile.getFilePointer());
+      }
     }
 
     // Task to dump the buffer cache to disk to guard against battery outages. The default is to run