copyin

[Conley%csvax.cs.ukans.edu at RELAY.CS.NET]

system: 780, 4.3

Well, a couple of us here have been mucking with a system call ( vhangup,
although that's not terribly important ). So we've tweaked the sysent
array, and added one of those mysterious struct a's to the code. Now, one
parameter is a string, and we use uap->string just like any other string
( e.g. in a tprintf ). However, an associate insists that this cannot be
done, i.e. the string exists in user space ( and this is kernel mode, hence
kernel address space ).

"Gotta do a copyin".

Dispensing with what we do ( and don't! ) know about the u area, kernel
stack, ( etc, etc ), how come our not doing this particular copyin doesn't
provoke crash and burn mode? The code works, we can print the silly thing,
yet it shouldn't work ( or should it? ).

Would anyone care to shed some light on this?


	Thanks for your time and patience.

	Dennis Conley
	Computer Science Dept
	University of Kansas

	CSNET:	conley at csvax.cs.ukans.edu
		conley at ukans.csnet            ( previously )

	BITNET:	conley at ukanvax


			"Onward through the fog!"