Implement RefCountDatabase methods in S3BackupFileSystem

lib/backupstore/BackupFileSystem.cpp

@@ -1263,13 +1263,54 @@ BackupStoreRefCountDatabase& S3BackupFileSystem::GetPermanentRefCountDatabase(
 
 BackupStoreRefCountDatabase& S3BackupFileSystem::GetPotentialRefCountDatabase()
 {
+	if(mapPotentialRefCountDatabase.get())
+	{
+		return *mapPotentialRefCountDatabase;
+	}
+
+	// Creating the "official" temporary refcount DB is actually a change
+	// to the cache, even if you don't commit it, because it's in the same
+	// directory and would conflict with another process trying to do the
+	// same thing, so it requires that you hold the write lock.
+	GetCacheLock();
+
+	// It's dangerous to have two read-write databases open at the same time (it would
+	// be too easy to update the refcounts in the wrong one by mistake), and temporary
+	// databases are always read-write, so if a permanent database is already open
+	// then it must be a read-only one.
+	ASSERT(!mapPermanentRefCountDatabase.get() ||
+		mapPermanentRefCountDatabase->IsReadOnly());
+
+	// The temporary database cannot be on the remote server, so there is no need to
+	// download it into the cache. Just create one and return it.
+	std::string local_path = GetRefCountDatabaseCachePath();
+
+	// We deliberately do not give the caller control of the
+	// reuse_existing_file parameter to Create(), because that would make
+	// it easy to bypass the restriction of only one (committable)
+	// temporary database at a time, and to accidentally overwrite the main
+	// refcount DB.
+	std::auto_ptr<BackupStoreRefCountDatabase> ap_new_db =
+		BackupStoreRefCountDatabase::Create(local_path, S3_FAKE_ACCOUNT_ID);
+	mapPotentialRefCountDatabase.reset(
+		new BackupStoreRefCountDatabaseWrapper(ap_new_db, *this));
+
 	return *mapPotentialRefCountDatabase;
 }
 
 
 void S3BackupFileSystem::SaveRefCountDatabase(BackupStoreRefCountDatabase& refcount_db)
 {
-	ASSERT(false);
+	// You can only save the permanent database.
+	ASSERT(&refcount_db == mapPermanentRefCountDatabase.get());
+
+	std::string local_path = GetRefCountDatabaseCachePath();
+	FileStream fs(local_path, O_RDONLY);
+
+	// Try to upload it to the remote server.
+	HTTPResponse response = mrClient.PutObject(GetMetadataURI(S3_REFCOUNT_FILE_NAME),
+		fs);
+	mrClient.CheckResponse(response, "Failed to upload refcount db to S3");
 }
 
 

lib/backupstore/BackupFileSystem.h

@@ -297,6 +297,10 @@ class S3BackupFileSystem : public BackupFileSystem
 	{
 		return (bytes + S3_NOTIONAL_BLOCK_SIZE - 1) / S3_NOTIONAL_BLOCK_SIZE;
 	}
+	std::string GetRefCountDatabaseCachePath()
+	{
+		return mCacheDirectory + DIRECTORY_SEPARATOR + S3_REFCOUNT_FILE_NAME;
+	}
 	void GetCacheLock();
 
 public: