/dev/null

[Stephen J. Muir]

>Seeing that /dev/mem and /dev/kmem are "windows" into the physical memory space
>of the computer, I wonder if /dev/null is implemented as a "window" into a
>nonexistent section of physical memory, or what?

cp /etc/motd /dev/null
panic: segmentation violation

What happens is that all writes map onto the "write" system call (write(2)).

The code (off the top of my head) goes like:

write (filedes, buffer, nbytes)
	char	*buffer
	{ if (major_minor (filedes) == that_of ("/dev/null"))
		return (nbytes);
	  else
		go_do_the_REAL_write (filedes, buffer, nbytes);
	}

So the "write" system call just returns success and does nothing!
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