CSE 121 Fa 2000 -- Lecture 3 -- Sep 28, 2000

The FreeBSD kernel sources are now in /home/solaris/ieng9/cs121f/public/freebsd/src/sys/ and a TAGS file is there, and it works well with emacs. Apparently vim has trouble with that file, so a CTAGS file (generated by the ctags program instead of etags) is also in the sys directory. vim works okay with it.

Things to explore:

You should familiarize yourself with using the TAGS file to find kernel symbols.
find hardclock and see what it's doing.
figure out what is going on in the code in kern_synch.c's mi_switch:
```
	rlim->rlim_cur += 5;
```
what does it do? what purpose does it serve?

Topics covered in today's lecture:

Job control and process group leaders. How shells use the job control mechanisms. Find the definition of TIOCGPGRP and TIOCSPGRP and how they're used in the kernel.
tty driver's distinguished process group. Comparison with the pre-BSD scheme -- do shells have to set signal handlers for background jobs now?
Signal delivery by the tty driver based on the intr, quit, susp characters. To which processes is the signal posted?
The ``silly script'':
```
$ cat ss
#!/bin/sh
cmd1&
cmd2&
$ ./ss > foo
```
and how the outputs from cmd1 and cmd2 are handled when foo is a file.
What happens if no output redirection occurs in ss or if the redirection is to a tty device? What are the SIGTTOU and SIGTTIN signals? See stty, in particular the tostop flag. Where in the kernel sources are these signals posted to processes?
The use of spl to set processor interrupt priority levels, shared data structures between top and bottom halves of the kernel, and implications wrt multiprocessors.

bsy+cse121.f00@cs.ucsd.edu, last updated Thu Oct 12 20:18:37 PDT 2000. Copyright 2000 Bennet Yee.
email bsy.