freebsd compile is so complicated? - freebsd

Question

I want to add custom syscall to freebsd(school work). I google hundreds of time. there is no right solution for it.
my homework is: "Add custom syscall to freebsd kernel and recompile the kernel and use it".
finally I find that I should follow instructions in these two pages:
1 : http://www.onlamp.com/pub/a/bsd/2003/10/09/adding_system_calls.html
then
2: https://www.freebsd.org/doc/en/books/handbook/kernelconfig-building.html
will it shows errors in compile time:
<sys/parma.h> no such file or directory
<sys/kern.h> no such file or directory
<sys/syscallargs.h> no such file or directory
I removed these three header include form my file then recompile it. now shows other errors like: MAXCPU undeclered in pcpu.h file.
what I missed? how can I do my school work?
NOTE: I use freebsd8 in vbox

Answer 1

Look at what the error messages say; the files don't exist.
The first include file is a typo; it's param.h, not parma.h!
There is no kern.h. Maybe you mean sys/kernel.h?
Idem for syscallargs.h. Do you perhaps mean syscall.h?
You can find header files with e.g:
find /usr/src/sys/ -type f -name '*.h'|grep 'sys/.*kern.*\.h'
/usr/src/sys/ofed/include/linux/kernel.h
/usr/src/sys/dev/netmap/netmap_kern.h
...
Update: More important is determining which includes you actually need.
FreeBSD has pretty good documentation. If you want to use a kernel function or data-structure, it is probably covered in section 9 of the manual pages.
You can list all the manual pages in that section with ls /usr/share/man/man9/ | less. Or you can use the apropos command.
Since you want to implement a syscall, start with e.g.
apropos syscall
It will return:
SYSCALL_MODULE(9) - syscall kernel module declaration macro
syscall(2), __syscall(2) - indirect system call
It seems to me that the first one could be relevant to your assignment. (The second one is how to call a system call from user space.) So read it with man SYSCALL_MODULE. Or read it online.
Note that:
A minimal example for a syscall module can be found in
/usr/share/examples/kld/syscall/module/syscall.c.
That example should be enough to get you started on writing your own system call module...

Answer 2

Well take a look at share/examples/kld/syscall for a complete implementation as a module.
Adding a new file to teh kernel is left as an exercise for the reader.
Here is a hint: find the newest added file within kern/* subdir AND CHECK WHAT COMMITS WERE DONE TO MAKE IT COMPILE.
In fact you could have done exactly the same with syscall: FIND THE NEWEST ADDED SYSCALL AND CHECK HOW IT WAS ACHIEVED.
All this is available in svn/git repository history.