In article <20010122181104.A1301@quartz.newn.cam.ac.uk> you write:
>I'm trying to get the kernel to fill in a SIMPLEQ, and reach it from userland
>via an ioctl.
>
>- Is there something simpler than a SIMPLEQ? (new to sys/queue.h)

SLIST is simpler in that it doesn't have a tail pointer (so you shouldn't
use it if you need a queue).  Alternatively, if you don't mind it being
expensive to dynamically grow the data, you could use a straightforward
array.  These are far easier to copy into user space.

>- Shouldn't I need a copyout or something? Don't see where though..

This is handled by sys_ioctl().  Look in sys/kern/sys_generic.c, and you'll
find that it does:

                error = (*fp->f_ops->fo_ioctl)(fp, com, data, p);
                if (error == 0 && (com&IOC_OUT) && size)
                        error = copyout(data, SCARG(uap, data), size);
                break;

Thus, all you need to do is to copy the data to the pointer you're given by
sys_ioctl(), and it will handle the copyout().

>Test userland prog works. With same function filling queue in kernel, I just
>get back null pointer, then again it doesn't surprise me too much, as I put
>a SIMPLEQ_HEAD in a header file, but what does a "global" variable mean when
>it appears in both kernel and executable - not very global anymore...

Indeed.  It's only global within the kernel.  Even if you got the address of
the structure into user space, this wouldn't help because user code can't
see kernel memory.

-- 
Ben Harris                                                   <bjh21@netbsd.org>
Portmaster, NetBSD/arm26               <URL:http://www.netbsd.org/Ports/arm26/>