Function AlterSystemSetConfigFile

src/backend/utils/misc/guc.c:8842–9047

* Execute ALTER SYSTEM statement. * * Read the old PG_AUTOCONF_FILENAME file, merge in the new variable value, * and write out an updated file. If the command is ALTER SYSTEM RESET ALL, * we can skip reading the old file and just write an empty file. * * An LWLock is used to serialize updates of the configuration file. * * In case of an error, we leave the original automatic * configurat

 * configuration file (PG_AUTOCONF_FILENAME) intact.
 */
void
AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
{
	char	   *name;
	char	   *value;
	bool		resetall = false;
	ConfigVariable *head = NULL;
	ConfigVariable *tail = NULL;
	volatile int Tmpfd;
	char		AutoConfFileName[MAXPGPATH];
	char		AutoConfTmpFileName[MAXPGPATH];

	if (!am_ftshandler && !superuser())
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 errmsg("must be superuser to execute ALTER SYSTEM command")));

	/*
	 * Extract statement arguments
	 */
	name = altersysstmt->setstmt->name;

	switch (altersysstmt->setstmt->kind)
	{
		case VAR_SET_VALUE:
			value = ExtractSetVariableArgs(altersysstmt->setstmt);
			break;

		case VAR_SET_DEFAULT:
		case VAR_RESET:
			value = NULL;
			break;

		case VAR_RESET_ALL:
			value = NULL;
			resetall = true;
			break;

		default:
			elog(ERROR, "unrecognized alter system stmt type: %d",
				 altersysstmt->setstmt->kind);
			break;
	}

	/*
	 * Unless it's RESET_ALL, validate the target variable and value
	 */
	if (!resetall)
	{
		struct config_generic *record;

		record = find_option(name, false, false, ERROR);
		Assert(record != NULL);

		/*
		 * Don't allow parameters that can't be set in configuration files to
		 * be set in PG_AUTOCONF_FILENAME file.
		 */