Remove some unused fields from InternalKey

Add them as unused fields in the TDEMapEntry structure however, so we
do not affect existing key files.

contrib/pg_tde/src/access/pg_tde_tdemap.c

@@ -56,7 +56,25 @@ typedef struct TDEMapEntry
 	Oid			spcOid;
 	RelFileNumber relNumber;
 	uint32		type;
-	InternalKey enc_key;
+
+	/*
+	 * This anonymous struct is here to ensure the same alignment as before
+	 * the unused fields were removed from InternalKey.
+	 */
+	struct
+	{
+		InternalKey enc_key;
+
+		/*
+		 * These fields were added here to keep the file format the same after
+		 * some fields were removed from InternalKey. Feel free to use them
+		 * for something, but beware that existing files may contain
+		 * unexpected values here.
+		 */
+		uint32		_unused1;	/* Will be 1 in existing files entries. */
+		uint64		_unused2;	/* Will be 0 in existing files entries. */
+	};
+
 	/* IV and tag used when encrypting the key itself */
 	unsigned char entry_iv[MAP_ENTRY_IV_SIZE];
 	unsigned char aead_tag[MAP_ENTRY_AEAD_TAG_SIZE];
@@ -210,9 +228,6 @@ pg_tde_free_key_map_entry(const RelFileLocator rlocator)
 		{
 			TDEMapEntry empty_map_entry = {
 				.type = MAP_ENTRY_EMPTY,
-				.enc_key = {
-					.type = MAP_ENTRY_EMPTY,
-				},
 			};
 
 			pg_tde_write_one_map_entry(map_fd, &empty_map_entry, &prev_pos, db_map_path);
@@ -407,9 +422,16 @@ pg_tde_initialize_map_entry(TDEMapEntry *map_entry, const TDEPrincipalKey *princ
 {
 	map_entry->spcOid = rlocator->spcOid;
 	map_entry->relNumber = rlocator->relNumber;
-	map_entry->type = rel_key_data->type;
+	map_entry->type = TDE_KEY_TYPE_SMGR;
 	map_entry->enc_key = *rel_key_data;
 
+	/*
+	 * We set these fields here so that existing file entries will be
+	 * consistent and future use of these fields easier.
+	 */
+	map_entry->_unused1 = 1;
+	map_entry->_unused2 = 0;
+
 	if (!RAND_bytes(map_entry->entry_iv, MAP_ENTRY_IV_SIZE))
 		ereport(ERROR,
 				errcode(ERRCODE_INTERNAL_ERROR),

contrib/pg_tde/src/encryption/enc_tde.c

@@ -27,11 +27,8 @@ iv_prefix_debug(const char *iv_prefix, char *out_hex)
 #endif
 
 void
-pg_tde_generate_internal_key(InternalKey *int_key, TDEMapEntryType entry_type)
+pg_tde_generate_internal_key(InternalKey *int_key)
 {
-	int_key->type = entry_type;
-	int_key->start_lsn = InvalidXLogRecPtr;
-
 	if (!RAND_bytes(int_key->key, INTERNAL_KEY_LEN))
 		ereport(ERROR,
 				errcode(ERRCODE_INTERNAL_ERROR),

contrib/pg_tde/src/include/access/pg_tde_tdemap.h

@@ -22,9 +22,6 @@ typedef struct InternalKey
 {
 	uint8		key[INTERNAL_KEY_LEN];
 	uint8		base_iv[INTERNAL_KEY_IV_LEN];
-	uint32		type;
-
-	XLogRecPtr	start_lsn;
 } InternalKey;
 
 #define MAP_ENTRY_IV_SIZE 16

contrib/pg_tde/src/include/encryption/enc_tde.h

@@ -7,7 +7,7 @@
 
 #include "access/pg_tde_tdemap.h"
 
-extern void pg_tde_generate_internal_key(InternalKey *int_key, TDEMapEntryType entry_type);
+extern void pg_tde_generate_internal_key(InternalKey *int_key);
 extern void pg_tde_stream_crypt(const char *iv_prefix,
 								uint32 start_offset,
 								const char *data,

contrib/pg_tde/src/smgr/pg_tde_smgr.c

@@ -75,7 +75,7 @@ tde_smgr_create_key(const RelFileLocatorBackend *smgr_rlocator)
 {
 	InternalKey *key = palloc_object(InternalKey);
 
-	pg_tde_generate_internal_key(key, TDE_KEY_TYPE_SMGR);
+	pg_tde_generate_internal_key(key);
 
 	if (RelFileLocatorBackendIsTemp(*smgr_rlocator))
 		tde_smgr_save_temp_key(&smgr_rlocator->locator, key);
@@ -105,7 +105,7 @@ tde_smgr_create_key_redo(const RelFileLocator *rlocator)
 	if (pg_tde_has_smgr_key(*rlocator))
 		return;
 
-	pg_tde_generate_internal_key(&key, TDE_KEY_TYPE_SMGR);
+	pg_tde_generate_internal_key(&key);
 
 	pg_tde_save_smgr_key(*rlocator, &key);
 }