[Coco] Telnet to your CoCo.. and invite 6 of your friends

[Boisy G. Pitre]

On Dec 1, 2009, at 4:55 PM, Willard Goosey wrote:

> On Tue, Dec 01, 2009 at 03:36:50PM -0600, Boisy G. Pitre wrote:
> 
>> That's exactly what would happen... when the kernel scans for krnpX
>> modules, it will call the os9 F$SSvc system call to install the
>> system calls in that module; if any of those system calls reuse an
>> existing system call number, then their address will overrwrite the
>> address stored in the system call jump table in RAM.
> 
> Well, that's the definitive answer from the definitive master. :-)

I appreciate the sentiment Willard, but there are other people who are more deserving of that moniker than I.

> That's really cool that a mechanism like that was already in place and
> running at a time when most operating systems, even for mainframes and
> minis, had completely statically linked kernels.

Not only that, but the "old" system call code is still in memory, so you can do some pretty neat things. Back at Microware, we would store off the original system call pointer; our custom system call would then do its thing (for example, increment a counter to keep track of the number of times a particular system call was called), then use the original pointer to jump to the old system call code.  This behavior is very much like class inheritance in object oriented languages.

>> It's a great way to extend the operating system.
> 
> Sounds really useful.
> 
> Willard
> -- 
> Willard Goosey  goosey at sdc.org
> Socorro, New Mexico, USA
> I search my heart and find Cimmeria, land of Darkness and the Night.
>  -- R.E. Howard
> 
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