Introduce postMount() VolumeBase helper.

When we're mounting a private volume, we create stacked emulated volumes
on top of it. Due to the ordering there, we would broadcast the emulated
volumes being created *before* the "mounted" status update. This in turn
could cause us to try and mount these emulated volumes before the
underlying private volume is really mounted. This is problematic in
particular on devices that support a filesystem keyring, where we need
to do some additional setup before the devices can be used.

While we could modify StorageManagerService to delay the mount, a safer
fix at this stage of the release is to just fix the ordering of these
events. To achieve that, add a simple postMount() helper, that is called
after a succesful mount. This allows us to setup the volume properly
before trying to mount any stacked volumes.

Bug: 151079464
Test: atest AdoptableHostTest
Change-Id: I2cc4113d4d71d89aa629bb9c0fa9be441355c079

model/PrivateVolume.cpp

@@ -177,6 +177,10 @@ status_t PrivateVolume::doMount() {
         return -EIO;
     }
 
+    return OK;
+}
+
+void PrivateVolume::doPostMount() {
     auto vol_manager = VolumeManager::Instance();
     std::string mediaPath(mPath + "/media");
 
@@ -189,8 +193,6 @@ status_t PrivateVolume::doMount() {
         addVolume(vol);
         vol->create();
     }
-
-    return OK;
 }
 
 status_t PrivateVolume::doUnmount() {

model/PrivateVolume.h

@@ -49,6 +49,7 @@ class PrivateVolume : public VolumeBase {
     status_t doCreate() override;
     status_t doDestroy() override;
     status_t doMount() override;
+    void doPostMount() override;
     status_t doUnmount() override;
     status_t doFormat(const std::string& fsType) override;
 

model/VolumeBase.cpp

@@ -232,9 +232,14 @@ status_t VolumeBase::mount() {
     status_t res = doMount();
     setState(res == OK ? State::kMounted : State::kUnmountable);
 
+    if (res == OK) {
+        doPostMount();
+    }
     return res;
 }
 
+void VolumeBase::doPostMount() {}
+
 status_t VolumeBase::unmount() {
     if (mState != State::kMounted) {
         LOG(WARNING) << getId() << " unmount requires state mounted";

model/VolumeBase.h

@@ -120,6 +120,7 @@ class VolumeBase {
     virtual status_t doCreate();
     virtual status_t doDestroy();
     virtual status_t doMount() = 0;
+    virtual void doPostMount();
     virtual status_t doUnmount() = 0;
     virtual status_t doFormat(const std::string& fsType);