preferable way to control kernel module

[John Baldwin]

On Wednesday 10 August 2005 05:50 pm, Sergey Uvarov wrote:
> >>>>I'm writing a kernel module for my own needs. AFAIK the following
> >>>>methods could be used:
> >>>>
> >>>>1) allocate not used system call with help of SYSCALL_MODULE macro
> >>>>
> >>>>2) allocate proprieatry oid via SYSCTL_OID(OID_AUTO) and write an
> >>>>appropriate sysctl handler(s)
> >>>>
> >>>>3) add a file in /dev and use ioctl(2) call
> >>>>
> >>>>What is a preferable way to control my module?
> >>>
> >>>It depends on what you want to do really.  I've used sysctl's for simple
> >>>debug modules where I write to the sysctl to have it perform a desired
> >>>action.
> >>
> >>I need to pass some configuration parameters to my module and retrieve a
> >>status back. Interface is quite similar to ptrace(2) syscall. I don't
> >>need to pass large amount of data.
> >
> > If it's a single integer or some such, I'd say use sysctl.  If it's a
> > structure, I'd go the ioctl(2) route.  Creating /dev entries isn't all
> > that hard.  In your case you'd just need open/close/ioctl in a cdevsw,
> > then use make_dev() during MOD_LOAD and destroy_dev() during MOD_UNLOAD.
>
> Thank you for advise. But I wonder: what is wrong with syscall approach
> (via SYSCALL_MODULE macro)?

I just haven't done one personally.  I think there's also a lot more potential 
for collisions when trying to pick a syscall number versus picking a string 
name for a sysctl or /dev entry.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org