Accesing vt(4) framebuffer

Hello, I'm developing a gui/widget over vt(4) framebuffer, no X11 nor
Wayland.

For this I have created a new ioctl that allows access to framebuffer
information and change it's content. For this I modified 
/usr/src/sys/dev/vt/hw/fb/vt_fb.c and .h, patches at end of this mail.

Is this a correct way? Should I do it different? Any security problems?

 
Thanks, Good Day.


--- vt_fb.h_ORIG	2025-08-21 19:01:01.192050000 +0200
+++ vt_fb.h	2025-08-21 19:04:58.447415000 +0200
@@ -49,4 +49,20 @@
 vd_fb_ioctl_t		vt_fb_ioctl;
 vd_fb_mmap_t		vt_fb_mmap;
 
+#ifdef _KERNEL
+#include <sys/ioccom.h>
+#endif
+
+/* Struct to expose framebuffer to userland*/
+struct vt_fb_userinfo {
+    uint32_t width;
+    uint32_t height;
+    uint32_t depth;
+    uint32_t stride;
+    uint32_t size;
+};
+
+/* IOCTL code to work with vt_fb_userinfo */
+#define VT_FB_GETINFO _IOR('v', 1, struct vt_fb_userinfo)
+
 #endif /* _DEV_VT_HW_FB_VT_FB_H_ */


--- vt_fb.c_ORIG	2025-08-21 19:01:07.096190000 +0200
+++ vt_fb.c	2025-08-21 19:10:22.228787000 +0200
@@ -42,6 +42,8 @@
 #include <vm/vm.h>
 #include <vm/pmap.h>
 
+#include <sys/ioccom.h> /* Userland access framebuffer */
+
 static struct vt_driver vt_fb_driver = {
 	.vd_name = "fb",
 	.vd_init = vt_fb_init,
@@ -87,6 +89,24 @@
 	*(uint32_t *)(sc->fb_vbase + o) = v;
 }
 
+static int
+vt_fb_userioctl(struct vt_device *vd, u_long cmd, caddr_t data)
+{
+    	struct vt_fb_userinfo *ui = (struct vt_fb_userinfo *)data;
+	struct fb_info *info = vd->vd_softc;
+
+    	if (cmd != VT_FB_GETINFO)
+        	return (ENOIOCTL);
+
+    	ui->width  = info->fb_width;
+	ui->height = info->fb_height;
+    	ui->depth  = info->fb_bpp * 8;
+    	ui->stride = info->fb_stride;
+    	ui->size   = info->fb_size;
+
+    	return (0);
+}
+
 int
 vt_fb_ioctl(struct vt_device *vd, u_long cmd, caddr_t data, struct thread *td)
 {
@@ -125,6 +145,10 @@
 			return (ENOTTY);
 		memcpy((struct fb_rgboffs *)data, &info->fb_rgboffs,
 		    sizeof(struct fb_rgboffs));
+		break;
+
+	case  VT_FB_GETINFO:   /* userland framebuffer */
+	        return vt_fb_userioctl(vd, cmd, data);
 		break;
 
 	default:


---   ---
Eduardo Morrás <emorras@emorras.eu>