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List:       freebsd-hackers
Subject:    how to have the kernel spawn a process?
From:       Alfred Perlstein <bright () hotjobs ! com>
Date:       1998-12-31 11:53:26
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I would like to have the kernel spawn a process and be able to control it.

1) fork1(&proc0, RFFDG|RFPROC)
2) cpu_set_fork_handler(pfind(proc0.p_retval[0]), &func_to_exec, args);
3) before execve'ing the process, set a flag to note that it's running,
the flag would have the pid if the current process. (normally it would be
0, or -1)
4) setup an at_exit() handler to reset the flag
5) overlay the vty of the current syscons screen over the stdin/stdout of
the process (*)
6) execve /usr/libexec/savers/mine

Basically i want syscons to be able to exec a usermode screensaver but
still maintain control over it in a failsafe fashion.  Something really
bugs me about screen savers being kernel modules. :)

if anyone wants to give hints as how to go about #5 i'd be much
appreciative.

note that when syscons gets input it can:

1) check the flag, (if 0, saver died, goto 8)
2) signal the screen saver for a graceful shutdown,
3) tsleep, 
4) check flag, (if 0, saver terminated gracefully(?), goto 8) 
5) kill -9, 
6) tsleep
7) check flag, (if !0, goto 6 (it has to die sometime right?)) 
8) restore screen.

(this might be invalid, i'm unsure if the input is at interupt time, or
normal time, but i'm sure i could hook it correctly)

suggestions? comments?

Alfred Perlstein - Programmer, HotJobs Inc. - www.hotjobs.com
-- There are operating systems, and then there's FreeBSD.
-- http://www.freebsd.org/                        3.0-current


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