libsnapshot: Ensure dm-user devices are destroyed after a merge.

Also, make sure snapuserd has closed its references. This is preventing
the merge from completing until a reboot.

Bug: N/A
Test: vts_libsnapshot_test
Change-Id: Iba18f887bdb262c630ec44461871e19fe64dbf3c

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -630,6 +630,9 @@ class SnapshotManager final : public ISnapshotManager {
     // The reverse of MapPartitionWithSnapshot.
     bool UnmapPartitionWithSnapshot(LockedFile* lock, const std::string& target_partition_name);
 
+    // Unmap a dm-user device through snapuserd.
+    bool UnmapDmUserDevice(const std::string& snapshot_name);
+
     // If there isn't a previous update, return true. |needs_merge| is set to false.
     // If there is a previous update but the device has not boot into it, tries to cancel the
     //   update and delete any snapshots. Return true if successful. |needs_merge| is set to false.

fs_mgr/libsnapshot/snapshot.cpp

@@ -1247,6 +1247,10 @@ bool SnapshotManager::CollapseSnapshotDevice(const std::string& name,
         return false;
     }
 
+    if (status.compression_enabled()) {
+        UnmapDmUserDevice(name);
+    }
+
     // Cleanup the base device as well, since it is no longer used. This does
     // not block cleanup.
     auto base_name = GetBaseDeviceName(name);
@@ -2063,27 +2067,8 @@ bool SnapshotManager::UnmapCowDevices(LockedFile* lock, const std::string& name)
 
     auto& dm = DeviceMapper::Instance();
 
-    auto dm_user_name = GetDmUserCowName(name);
+    if (IsCompressionEnabled() && !UnmapDmUserDevice(name)) {
-    if (IsCompressionEnabled() && dm.GetState(dm_user_name) != DmDeviceState::INVALID) {
+        return false;
-        if (!EnsureSnapuserdConnected()) {
-            return false;
-        }
-        if (!dm.DeleteDeviceIfExists(dm_user_name)) {
-            LOG(ERROR) << "Cannot unmap " << dm_user_name;
-            return false;
-        }
-
-        if (!snapuserd_client_->WaitForDeviceDelete(dm_user_name)) {
-            LOG(ERROR) << "Failed to wait for " << dm_user_name << " control device to delete";
-            return false;
-        }
-
-        // Ensure the control device is gone so we don't run into ABA problems.
-        auto control_device = "/dev/dm-user/" + dm_user_name;
-        if (!android::fs_mgr::WaitForFileDeleted(control_device, 10s)) {
-            LOG(ERROR) << "Timed out waiting for " << control_device << " to unlink";
-            return false;
-        }
     }
 
     auto cow_name = GetCowName(name);
@@ -2100,6 +2085,37 @@ bool SnapshotManager::UnmapCowDevices(LockedFile* lock, const std::string& name)
     return true;
 }
 
+bool SnapshotManager::UnmapDmUserDevice(const std::string& snapshot_name) {
+    auto& dm = DeviceMapper::Instance();
+
+    if (!EnsureSnapuserdConnected()) {
+        return false;
+    }
+
+    auto dm_user_name = GetDmUserCowName(snapshot_name);
+    if (dm.GetState(dm_user_name) == DmDeviceState::INVALID) {
+        return true;
+    }
+
+    if (!dm.DeleteDeviceIfExists(dm_user_name)) {
+        LOG(ERROR) << "Cannot unmap " << dm_user_name;
+        return false;
+    }
+
+    if (!snapuserd_client_->WaitForDeviceDelete(dm_user_name)) {
+        LOG(ERROR) << "Failed to wait for " << dm_user_name << " control device to delete";
+        return false;
+    }
+
+    // Ensure the control device is gone so we don't run into ABA problems.
+    auto control_device = "/dev/dm-user/" + dm_user_name;
+    if (!android::fs_mgr::WaitForFileDeleted(control_device, 10s)) {
+        LOG(ERROR) << "Timed out waiting for " << control_device << " to unlink";
+        return false;
+    }
+    return true;
+}
+
 bool SnapshotManager::MapAllSnapshots(const std::chrono::milliseconds& timeout_ms) {
     auto lock = LockExclusive();
     if (!lock) return false;