Re: Selecting the scheduler from boot menu

On Sat, 31 Jan 2026 23:15:49 +0100
Milan Obuch <freebsd-hackers@dino.sk> wrote:

> On Sat, 31 Jan 2026 12:44:07 -0800
> Steve Kargl <kargls@comcast.net> wrote:
> 
> > On 1/31/26 12:35, Milan Obuch wrote:  
> > > On Sat, 31 Jan 2026 12:21:59 -0800
> > > Steve Kargl <kargls@comcast.net> wrote:
> > >     
> > >> All,
> > >>
> > >> Is it possible modify the boot menu to select 4BSD or ULE during
> > >> the boot process?  I've looked at the code in src/stand/forth,
> > >> but unfortunately the language is foreign to me. Currently, one
> > >> boots into FreeBSD, checks the kern.sched.name, and then may
> > >> need to edit /boot/loader.conf to change to the other scheduler,
> > >> and then reboot.   
> > > 
> > > Which version are you working on? I think something recent, maybe
> > > 16-CURRENT. Loader was rewritten in lua some time ago.    
> > 
> > I'm looking at src/stand/forth, particular, menu-commands.4th.  
> 
> Somehow, those old files are still present and installed, but no
> longer used in boot process unless some non-standard build or
> configuration is being used.
> 
> > If the boot menu is written in lua, it's still a foreign language to
> > me. So, I would need some guidance on how to hack the menu up.
> > 
> > Yes, it is a convenience to have menu item. Dropping to the loader
> > prompt is possible. Taking it to a logical extreme, let's retire the
> > menu because everything can be set at the loader prompt.  
> 
> I'll try to look there. I did not actually read files in /boot/lua
> directory yet, but I have some lua experience and maybe I can come
> with something if nobody acts quicker... but first I nedd to
> understand the process.
> 

There is menu.lua file with all boot menu related functionality. Now
the question is, where should the new option go - there is main menu
loaded upon start, and then options menu could be invoked from there.
As an option for 4BSD/ULE scheduler selection, it should go probably to
the later. A word of warning, all options changed via options menu are
not persistent, so on next reboot default value (with possible override
by config file vale) is used.

Regards,
Milan