Re: Writing system calls.

["Bob Dilworth" <bdilworth@mco.edu>]

>Does anyone know a good documentation about writing new system calls ??

Hi Radu!

Conventional wisdom has it that writing new system calls is not a good idea.  Apparently all new calls have to be approved by Mr. Torvalds (each call has its own number) and adding one for your own personal enjoyment and edification may interfere with new ones added to new kernels forcing you to re-code and re-compile your own personal ones.  The better strategy, again according to conventional widsom, is to write a module that supports IOCTL (spelling?) fuctions.  Please note that the above caveat may not be totally accurate but that's the jist of it I've put together by lurking on this august list.

That said it seems to me that if you're thinking of writing a new system call for your own  enjoyment and learning experience, I say go for it!  How else would one learn how to do it except by, well, actually doing it.  As long as you're aware of the conventional wisdom and it's various caveats I see no harm in having a personal kernel with one's own system calls embedded therein.  If you decide to go this route and ask for help, be prepared for folks telling you shouldn't be doing that.  Also be prepared to tell them that you're doing it for your own education and don't plan on putting the system call into a production system, etc., etc.

I've written one module (proc file) and found that the Linux Kernel Module Programming Guide by Ori Pommeratz (spelling) is invaluable.  Here's a link to a page from which you can download the Guide ( http://howto.tucows.com/guides.html ).  I'd also recommend the new O'Reilly "Understanding the Linux Kernel book.  Between the Module Programming Guide, the O'Reilly book, the helpful folks on this list, and hitting the right keys on the keyboard in the right order, it was a snap ;-)

Remember - have fun, keep an open mind, be prepared for varying degrees of frustration, and ask for help.  You'll find folks are very patient and extremely helpful.

Welcome aboard!!!!!!!!!!

Bob Dilworth
Medical College of Ohio
Toledo, Ohio
(419)383-6071
bdilworth@mco.edu

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