vt(4): Add PIO_VFONT_DEFAULT ioctl to restore the default builtin font

To restore the default font using vidcontrol(1), use the "-f" flag
without an argument:
    vidcontrol -f < /dev/ttyv0

PR:		193910
Differential Revision:	https://reviews.freebsd.org/D971
Submitted by:	Marcin Cieslak <saper@saper.info>
Reviewed by:	ray@, emaste@
Approved by:	ray@
MFC after:	1 week

sys/dev/vt/vt_core.c

@@ -2218,6 +2218,11 @@ vtterm_ioctl(struct terminal *tm, u_long cmd, caddr_t data,
 		vtfont_unref(vf);
 		return (error);
 	}
+	case PIO_VFONT_DEFAULT: {
+		/* Reset to default font. */
+		error = vt_change_font(vw, &vt_font_default);
+		return (error);
+	}
 	case GIO_SCRNMAP: {
 		scrmap_t *sm = (scrmap_t *)data;
 

sys/sys/consio.h

@@ -239,6 +239,7 @@ typedef struct vfnt	vfnt_t;
 #define GIO_FONT8x16	_IOR('c', 69, fnt16_t)
 #define PIO_VFONT	_IOW('c', 70, vfnt_t)
 #define GIO_VFONT	_IOR('c', 71, vfnt_t)
+#define PIO_VFONT_DEFAULT _IO('c', 72)
 
 /* get video mode information */
 struct colors	{

usr.sbin/vidcontrol/vidcontrol.1

@@ -26,9 +26,11 @@
 .Op Fl c Ar appearance
 .Oo
 .Fl f
+.Oo
 .Op Ar size
 .Ar file
 .Oc
+.Oc
 .Op Fl g Ar geometry
 .Op Fl h Ar size
 .Op Fl i Cm adapter | mode
@@ -136,8 +138,10 @@ The latter is actually a simulation.
 Print out current output screen map.
 .It Xo
 .Fl f
+.Oo
 .Op Ar size
 .Ar file
+.Oc
 .Xc
 Load font
 .Ar file
@@ -158,6 +162,14 @@ may be omitted, in this case
 .Nm
 will try to guess it from the size of font file.
 .Pp
+When using
+.Xr vt 4
+both
+.Ar size
+and
+.Ar font
+can be omitted, and the default font will be loaded.
+.Pp
 Note that older video cards, such as MDA and CGA, do not support
 software font.
 See also

usr.sbin/vidcontrol/vidcontrol.c

@@ -197,7 +197,7 @@ usage(void)
 {
 	if (vt4_mode)
 		fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n",
-"usage: vidcontrol [-CHPpx] [-b color] [-c appearance] [-f [size] file]",
+"usage: vidcontrol [-CHPpx] [-b color] [-c appearance] [-f [[size] file]]",
 "                  [-g geometry] [-h size] [-i adapter | mode]",
 "                  [-M char] [-m on | off] [-r foreground background]",
 "                  [-S on | off] [-s number] [-T xterm | cons25] [-t N | off]",
@@ -409,6 +409,19 @@ load_vt4mappingtable(unsigned int nmappings, FILE *f)
 	return (t);
 }
 
+/*
+ * Set the default vt font.
+ */
+
+static void
+load_default_vt4font(void)
+{
+	if (ioctl(0, PIO_VFONT_DEFAULT) == -1) {
+		revert();
+		errc(1, errno, "loading default vt font");
+	}
+}
+
 static int
 load_vt4font(FILE *f)
 {
@@ -1328,7 +1341,7 @@ main(int argc, char **argv)
 	dumpopt = DUMP_FBF;
 	termmode = NULL;
 	if (vt4_mode)
-		opts = "b:Cc:f:g:h:Hi:M:m:pPr:S:s:T:t:x";
+		opts = "b:Cc:fg:h:Hi:M:m:pPr:S:s:T:t:x";
 	else
 		opts = "b:Cc:df:g:h:Hi:l:LM:m:pPr:S:s:T:t:x";
 
@@ -1349,15 +1362,23 @@ main(int argc, char **argv)
 			print_scrnmap();
 			break;
 		case 'f':
-			type = optarg;
+			optarg = nextarg(argc, argv, &optind, 'f', 0);
-			font = nextarg(argc, argv, &optind, 'f', 0);
+			if (optarg != NULL) {
+				font = nextarg(argc, argv, &optind, 'f', 0);
 
-			if (font == NULL) {
+				if (font == NULL) {
-				type = NULL;
+					type = NULL;
-				font = optarg;
+					font = optarg;
+				} else
+					type = optarg;
+
+				load_font(type, font);
+			} else {
+				if (!vt4_mode)
+					usage(); /* Switch syscons to ROM? */
+
+				load_default_vt4font();
 			}
-
-			load_font(type, font);
 			break;
 		case 'g':
 			if (sscanf(optarg, "%dx%d",