Refactor InitPostgres() to use bitwise option flags

InitPostgres() has been using a set of boolean arguments to control its
behavior, and a patch under discussion was aiming at expanding it with a
third one.  In preparation for expanding this area, this commit switches
all the current boolean arguments of this routine to a single bits32
argument instead.  Two values are currently supported for the flags:
- INIT_PG_LOAD_SESSION_LIBS to load [session|local]_preload_libraries at
startup.
- INIT_PG_OVERRIDE_ALLOW_CONNS to allow connection to a database even if
it has !datallowconn.  This is used by bgworkers.

Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/ZSTn66_BXRZCeaqS@paquier.xyz

src/backend/bootstrap/bootstrap.c

@@ -345,7 +345,7 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
 	if (pg_link_canary_is_frontend())
 		elog(ERROR, "backend is incorrectly linked to frontend functions");
 
-	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, false, false, NULL);
+	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, 0, NULL);
 
 	/* Initialize stuff for bootstrap-file processing */
 	for (i = 0; i < MAXATTR; i++)

src/backend/postmaster/autovacuum.c

@@ -488,7 +488,7 @@ AutoVacLauncherMain(int argc, char *argv[])
 	/* Early initialization */
 	BaseInit();
 
-	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, false, false, NULL);
+	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, 0, NULL);
 
 	SetProcessingMode(NormalProcessing);
 
@@ -1706,8 +1706,7 @@ AutoVacWorkerMain(int argc, char *argv[])
 		 * Note: if we have selected a just-deleted database (due to using
 		 * stale stats info), we'll fail and exit here.
 		 */
-		InitPostgres(NULL, dbid, NULL, InvalidOid, false, false,
-					 dbname);
+		InitPostgres(NULL, dbid, NULL, InvalidOid, 0, dbname);
 		SetProcessingMode(NormalProcessing);
 		set_ps_display(dbname);
 		ereport(DEBUG1,

src/backend/postmaster/postmaster.c

@@ -5562,6 +5562,11 @@ void
 BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags)
 {
 	BackgroundWorker *worker = MyBgworkerEntry;
+	bits32		init_flags = 0; /* never honor session_preload_libraries */
+
+	/* ignore datallowconn? */
+	if (flags & BGWORKER_BYPASS_ALLOWCONN)
+		init_flags |= INIT_PG_OVERRIDE_ALLOW_CONNS;
 
 	/* XXX is this the right errcode? */
 	if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
@@ -5571,8 +5576,7 @@ BackgroundWorkerInitializeConnection(const char *dbname, const char *username, u
 
 	InitPostgres(dbname, InvalidOid,	/* database to connect to */
 				 username, InvalidOid,	/* role to connect as */
-				 false,			/* never honor session_preload_libraries */
-				 (flags & BGWORKER_BYPASS_ALLOWCONN) != 0,	/* ignore datallowconn? */
+				 init_flags,
 				 NULL);			/* no out_dbname */
 
 	/* it had better not gotten out of "init" mode yet */
@@ -5589,6 +5593,11 @@ void
 BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
 {
 	BackgroundWorker *worker = MyBgworkerEntry;
+	bits32		init_flags = 0; /* never honor session_preload_libraries */
+
+	/* ignore datallowconn? */
+	if (flags & BGWORKER_BYPASS_ALLOWCONN)
+		init_flags |= INIT_PG_OVERRIDE_ALLOW_CONNS;
 
 	/* XXX is this the right errcode? */
 	if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
@@ -5598,8 +5607,7 @@ BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
 
 	InitPostgres(NULL, dboid,	/* database to connect to */
 				 NULL, useroid, /* role to connect as */
-				 false,			/* never honor session_preload_libraries */
-				 (flags & BGWORKER_BYPASS_ALLOWCONN) != 0,	/* ignore datallowconn? */
+				 init_flags,
 				 NULL);			/* no out_dbname */
 
 	/* it had better not gotten out of "init" mode yet */

src/backend/tcop/postgres.c

@@ -4206,11 +4206,12 @@ PostgresMain(const char *dbname, const char *username)
 	 * NOTE: if you are tempted to add code in this vicinity, consider putting
 	 * it inside InitPostgres() instead.  In particular, anything that
 	 * involves database access should be there, not here.
+	 *
+	 * Honor session_preload_libraries if not dealing with a WAL sender.
 	 */
 	InitPostgres(dbname, InvalidOid,	/* database to connect to */
 				 username, InvalidOid,	/* role to connect as */
-				 !am_walsender, /* honor session_preload_libraries? */
-				 false,			/* don't ignore datallowconn */
+				 (!am_walsender) ? INIT_PG_LOAD_SESSION_LIBS : 0,
 				 NULL);			/* no out_dbname */
 
 	/*

src/backend/utils/init/postinit.c

@@ -681,8 +681,9 @@ BaseInit(void)
  * Parameters:
  *	in_dbname, dboid: specify database to connect to, as described below
  *	username, useroid: specify role to connect as, as described below
- *	load_session_libraries: TRUE to honor [session|local]_preload_libraries
- *	override_allow_connections: TRUE to connect despite !datallowconn
+ *	flags:
+ *	  - INIT_PG_LOAD_SESSION_LIBS to honor [session|local]_preload_libraries.
+ *	  - INIT_PG_OVERRIDE_ALLOW_CONNS to connect despite !datallowconn.
  *	out_dbname: optional output parameter, see below; pass NULL if not used
  *
  * The database can be specified by name, using the in_dbname parameter, or by
@@ -701,8 +702,8 @@ BaseInit(void)
  * database but not a username; conversely, a physical walsender specifies
  * username but not database.
  *
- * By convention, load_session_libraries should be passed as true in
- * "interactive" sessions (including standalone backends), but false in
+ * By convention, INIT_PG_LOAD_SESSION_LIBS should be passed in "flags" in
+ * "interactive" sessions (including standalone backends), but not in
  * background processes such as autovacuum.  Note in particular that it
  * shouldn't be true in parallel worker processes; those have another
  * mechanism for replicating their leader's set of loaded libraries.
@@ -717,8 +718,7 @@ BaseInit(void)
 void
 InitPostgres(const char *in_dbname, Oid dboid,
 			 const char *username, Oid useroid,
-			 bool load_session_libraries,
-			 bool override_allow_connections,
+			 bits32 flags,
 			 char *out_dbname)
 {
 	bool		bootstrap = IsBootstrapProcessingMode();
@@ -1189,7 +1189,8 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	 * user is a superuser, so the above stuff has to happen first.)
 	 */
 	if (!bootstrap)
-		CheckMyDatabase(dbname, am_superuser, override_allow_connections);
+		CheckMyDatabase(dbname, am_superuser,
+						(flags & INIT_PG_OVERRIDE_ALLOW_CONNS) != 0);
 
 	/*
 	 * Now process any command-line switches and any additional GUC variable
@@ -1227,7 +1228,7 @@ InitPostgres(const char *in_dbname, Oid dboid,
 	 * during the initial transaction in case anything that requires database
 	 * access needs to be done.
 	 */
-	if (load_session_libraries)
+	if ((flags & INIT_PG_LOAD_SESSION_LIBS) != 0)
 		process_session_preload_libraries();
 
 	/* report this backend in the PgBackendStatus array */

src/include/miscadmin.h

@@ -463,12 +463,14 @@ extern PGDLLIMPORT AuxProcType MyAuxProcType;
  *****************************************************************************/
 
 /* in utils/init/postinit.c */
+/* flags for InitPostgres() */
+#define INIT_PG_LOAD_SESSION_LIBS		0x0001
+#define INIT_PG_OVERRIDE_ALLOW_CONNS	0x0002
 extern void pg_split_opts(char **argv, int *argcp, const char *optstr);
 extern void InitializeMaxBackends(void);
 extern void InitPostgres(const char *in_dbname, Oid dboid,
 						 const char *username, Oid useroid,
-						 bool load_session_libraries,
-						 bool override_allow_connections,
+						 bits32 flags,
 						 char *out_dbname);
 extern void BaseInit(void);