Ignore interrupt in system() calls?

[thompson at uxf.cso.uiuc.edu]

4.3 BSD on a Sequent, if that makes much of a difference.

I am writing a C-shell-script/C-program pair to securely allow handing in
 of programs by students.  One of the things I'd like to do is turn off
 the two keyboard-initiated interrupts over the critical handing-in portion
 of the code.  Last year, I got quite enough of the "but it was taking so long,
 I just stopped it, but I thought it was handed in...".

Luckily, the critical portion is in the C program.  So, I stuck:

signal (SIGINT,SIG_IGN);
signal (SIGQUIT,SIG_IGN);

at the top of the C program and figured I was fine.  But after tracking some
strange occurrences, I noticed that when I do the "system()" calls I need to
do later in the program, the signals are reset to be trapped normally in
the shell that's forked by system().  So if a student hits CTRL-C while it's
executing the system(), it's trapped, and I'm out of luck.

So, I need one of three things:

1. A way for my interrupt ignoring to be passed to my system() shells.
2. A way for me to set the interrupts to be ignored in the midst of my
	system() calls.
or
3. A way to "chmod" files from within a C program without using "system()".

Thanks in advance,


- Mark Thompson                       "The University Neither Knows Nor
"The less I seek my source for some     Cares What I Am Saying -- Lucky
 definitive, closer I am to fine."      Them."
  University of Illinois at U-C
  INTERNET: thompson at uxf.cso.uiuc.edu
  USMAILNET: 202 E Springfield #3B, Champaign IL 61820