Re: 1.6 and /dev/reload

[Gunther Nikl <gni%gecko.de@localhost>]

Hello,

> >   I modified kernel_reload_write() to handle ELF kernels and now I have
> >   a functional /dev/reload again. I removed the aout stuff since it does
> >   not make any sense on an ELF system, IMO.
> 
> Now that it is working for recent systems, maybe this is a good time to
> ask: What does it do? I have a general idea (is it right?) that it allows
> one to reboot a new kernel without rebooting the whole system from the
> ROMs?

  Almost. You can't reboot any kernel: the "new" kernel must be very
  similiar to your currently running kernel. I don't know why thats
  important (there is a check in locore.s/kernel_reload). Another
  shortcoming is that chipmem is used during reboot. Your kernel must
  be smaller than chipmem size. And I forgot to say, that loading symbols
  isn't supported. Doing that was already hard with a.out kernels and it
  looks like its nearly impossible for ELF kernels. /dev/reload is a pipe
  device and loading symbols would require seeking.

> >   The new code isn't finished yet, some tweaks are still to be done. I
> >   would like to get rid of the chipmem requirement. Is this possible?
> >   Another thought is, to only allow reboot if the machine is in single
> >   user mode.
> 
> (Forgive my ignorance; I'm guessing) Wouldn't it be better to use
> /dev/reload with reboot so that reboot with a flag can bring the
> system into single user mode, then use /dev/reload?

  A "normal" reboot doesn't directly reboot into a new kernel, it transfers
  the control ROM. Limitting /dev/reload to single user was probably a bad
  idea since then you must be on the console to reboot.

> How does one use /dev/reload? I see no man page...

  Like this: cp <kernel> /dev/reload

  Gunther

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 - Jamie Zawinsky