Optionally include a DEFAULTS config file if it is present in the current

directory before the specified config file.  This is implemented by
opening DEFAULTS as stdin if it exists, and if so resetting stdin to the
actual config file when DEFAULTS is fully parsed via yywrap().  In short,
this lets us create DEFAULTS kernel configs in /sys/<arch>/conf that can
enable certain options or devices by default and allow users to disable
them via 'nooptions' or 'nodevice' rather than having to create kludge
NO_FOO options.

Requested by:	scottl
Reviewed by:	scottl

1 files changed, 16 insertions, 0 deletions

diff --git a/usr.sbin/config/config.y b/usr.sbin/config/config.y
index 018ec61..58d6b0c 100644
--- a/usr.sbin/config/config.y
+++ b/usr.sbin/config/config.y
@@ -92,6 +92,7 @@ int	maxusers;
 #define ns(s)	strdup(s)
 int include(const char *, int);
 void yyerror(const char *s);
+int yywrap(void);
 
 static char *
 devopt(char *dev)
@@ -300,6 +301,21 @@ yyerror(const char *s)
 	errx(1, "%s:%d: %s", yyfile, yyline + 1, s);
 }
 
+int
+yywrap(void)
+{
+
+	if (found_defaults) {
+		if (freopen(PREFIX, "r", stdin) == NULL)
+			err(2, "%s", PREFIX);		
+		yyfile = PREFIX;
+		yyline = 0;
+		found_defaults = 0;
+		return 0;
+	}
+	return 1;
+}
+
 /*
  * Add a new file to the list of files.
  */