Re: Accesing vt(4) framebuffer

hi!

We put code review requests in the tool at https://reviews.freebsd.org/ .
If you've not heard back about this
then please feel free to poke me directly.

Having direct fb access from userland would be great. I thought we already
did?!



-adrian

On Tue, 26 Aug 2025 at 07:10, Eduardo Morrás <emorras@emorras.eu> wrote:

>
> 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>
>
>