Re: Reasons for keeping sc(4) and libvgl ?

From: Marek Zarychta <>
Date: Fri, 26 Nov 2021 19:17:00 UTC
Honourable committers, dear subscribers,

W dniu 26.11.2021 o 16:04, Emmanuel Vadot pisze:
>   Hello all,
>   I'm currently re-implementing the framebuffer code in linuxkpi for
> drm-kmod and this made me look at sc(4), vt(4) and friends.
>   So I looked at what sc could do and vt couldn't and vice-versa.
>   What sc(4) can't do :
>   - Work with EFI firmware.
>   - Support UTF-8
>   - Maybe other things but everything here is EFI-based so let me know.
>   What vt(4) can't do :
>   - You can't get the modes or adapter info with vidcontrol.
>     vidcontrol -i mode is really made for anything vesa based as it
> iterates on all the modes and display them if present.
>     In the modern world (EFI), we don't have that, EFI GOP doesn't
> support changing resolution after ExitBootService was called so there
> is only one "mode". I could possibly hack some patch so vidcontrol -i
> mode/adapter would work and display the current framebuffer info if
> people wants (but I honestly doubt that vidcontrol is useful at all in
> an EFI world).
>   - "Blanking" screen doesn't do what you think it does. For some reason
> in vt(4) we just write black colors on the screen and ignore the blank
> mode passed in the ioctl.
>     Now again, blanking/dpms/blah isn't possible with efi_fb but it make
> sense to fix vt(4) and drm-kmod so it calls the drm module blanking
> function, I'll work on that next week.
>    - There is no screensaver, again see notes above for dpms but do
> people still use sc(4) just for the screensaver ??
>    - Maybe other things, please let me know.
>   For libvgl it probably made sense back in the 90s but does it now ??
>   Based on my small list I don't see any good reason to keep sc(4) but
> maybe I've missed something bigger so please let me know.
>   P.S.: I'm really not interested by people saying stuff like
>   "I've always used sc(4), it works for me don't touch it"
>   without some technical argument.
>   Cheers,
I responded to this inquiry on IRC earlier, but will also give some 
feedback here.

There is only one reason for me to still use sc(4) on a few amd64 
machines not running X11 servers which have either old KVMs or directly 
connected monitors: the ability to use saver(4) with green_saver.ko 
which can power off the monitor via DPMS. Probably it is one of the most 
missing features of vt(4).


Marek Zarychta
FreeBSD user since mid-1990s