Merge "Helper function to mount snapshot devices in recovery"

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -74,6 +74,12 @@ static constexpr const std::string_view kCowGroupName = "cow";
 
 bool SourceCopyOperationIsClone(const chromeos_update_engine::InstallOperation& operation);
 
+enum class CreateResult : unsigned int {
+    ERROR,
+    CREATED,
+    NOT_CREATED,
+};
+
 enum class UpdateState : unsigned int {
     // No update or merge is in progress.
     None,
@@ -246,6 +252,17 @@ class SnapshotManager final {
     // optional callback fires periodically to query progress via GetUpdateState.
     bool HandleImminentDataWipe(const std::function<void()>& callback = {});
 
+    // This method is only allowed in recovery and is used as a helper to
+    // initialize the snapshot devices as a requirement to mount a snapshotted
+    // /system in recovery.
+    // This function returns:
+    // - CreateResult::CREATED if snapshot devices were successfully created;
+    // - CreateResult::NOT_CREATED if it was not necessary to create snapshot
+    // devices;
+    // - CreateResult::ERROR if a fatal error occurred, mounting /system should
+    // be aborted.
+    CreateResult RecoveryCreateSnapshotDevices();
+
     // Dump debug information.
     bool Dump(std::ostream& os);
 

fs_mgr/libsnapshot/snapshot.cpp

@@ -2356,5 +2356,37 @@ bool SnapshotManager::EnsureNoOverflowSnapshot(LockedFile* lock) {
     return true;
 }
 
+CreateResult SnapshotManager::RecoveryCreateSnapshotDevices() {
+    if (!device_->IsRecovery()) {
+        LOG(ERROR) << __func__ << " is only allowed in recovery.";
+        return CreateResult::NOT_CREATED;
+    }
+
+    auto mount = EnsureMetadataMounted();
+    if (!mount || !mount->HasDevice()) {
+        LOG(ERROR) << "Couldn't mount Metadata.";
+        return CreateResult::NOT_CREATED;
+    }
+
+    auto state_file = GetStateFilePath();
+    if (access(state_file.c_str(), F_OK) != 0 && errno == ENOENT) {
+        LOG(ERROR) << "Couldn't access state file.";
+        return CreateResult::NOT_CREATED;
+    }
+
+    if (!NeedSnapshotsInFirstStageMount()) {
+        return CreateResult::NOT_CREATED;
+    }
+
+    auto slot_suffix = device_->GetOtherSlotSuffix();
+    auto slot_number = SlotNumberForSlotSuffix(slot_suffix);
+    auto super_path = device_->GetSuperDevice(slot_number);
+    if (!CreateLogicalAndSnapshotPartitions(super_path)) {
+        LOG(ERROR) << "Unable to map partitions.";
+        return CreateResult::ERROR;
+    }
+    return CreateResult::CREATED;
+}
+
 }  // namespace snapshot
 }  // namespace android