PG-2379 Allow different principal keys for relation key file migration

The code assumed that all databases would use the same principal key
which is generally not true. This fix loads the principal key for each
database as needed.

Author: AndersAstrand

src/access/pg_tde_tdemap.c

@@ -989,8 +989,6 @@ pg_tde_migrate_smgr_keys_file(void)
 	DIR		   *dir;
 	LWLock	   *lock_pk = tde_lwlock_enc_keys();
 	struct dirent *file;
-	TDEPrincipalKey *principal_key = NULL;
-	TDESignedPrincipalKeyInfo signed_key_info;
 
 	/*
 	 * No real need in lock here as the func should be called only on the
@@ -1016,6 +1014,8 @@ pg_tde_migrate_smgr_keys_file(void)
 		TDEFileHeader fheader;
 		MapFromDiskEntry read_map_entry;
 		TDEMapEntry new_entry;
+		TDEPrincipalKey *principal_key;
+		TDESignedPrincipalKeyInfo signed_key_info;
 
 
 		dbOid = strtoul(file->d_name, &suffix, 10);
@@ -1047,17 +1047,14 @@ pg_tde_migrate_smgr_keys_file(void)
 		 * The old file exists and it's not empty, hence a principal key
 		 * should exist as well.
 		 */
+		principal_key = GetPrincipalKey(dbOid, LW_EXCLUSIVE);
 		if (principal_key == NULL)
 		{
-			principal_key = GetPrincipalKey(dbOid, LW_EXCLUSIVE);
-			if (principal_key == NULL)
-			{
-				ereport(ERROR,
-						errmsg("could not get server principal key"),
-						errdetail("Failed to migrate the keys file of %u database.", dbOid));
-			}
-			pg_tde_sign_principal_key_info(&signed_key_info, principal_key);
+			ereport(ERROR,
+					errmsg("failed to retrieve principal key for database %u", dbOid),
+					errdetail("Failed to migrate the keys file of database %u.", dbOid));
 		}
+		pg_tde_sign_principal_key_info(&signed_key_info, principal_key);
 
 		new_fd = pg_tde_open_file_write(tmp_db_map_path, &signed_key_info, true, &write_pos);