Re: More serial ports in EFI bootstrap?

On Wed, Jun 04, 2025 at 01:27:39PM +0000, Emmanuel Dreyfus wrote:
> On Wed, Jun 04, 2025 at 09:05:36AM -0400, Thor Lancelot Simon wrote:
> > Can (and should) we access the console via EFI interfaces in this case?
> 
> You can skip the call to UEFI ExitBootServices() but I guess you need
> to take care of not overwriting memory used by UEFI. I recall doing
> that to get console output later during kernel load process. It worked, 
> but I did not try to call UEFI Read/Write from the kernel.

It seems to me that -- ideally -- we wouldn't ExitBootServices until we
had finished probe and attach of all devices needed to get the system to
single-user mode.  But maybe the console is the only one that's really in
that category, the way our current boot process works even if netbooting.

I suppose it's a worthwhile question whether the probe/attach for a USB
serial console will actually work properly if we haven't called
ExitBootServices, but I'd hope the answer is that it's sufficient to do
immediately _afterwards_.

Thor