Re: order of executing MOD_LOAD and registering module sysctl-s

On Wednesday, August 02, 2017 12:39:36 PM Hans Petter Selasky wrote:
> On 08/02/17 12:13, Andriy Gapon wrote:
> > 
> > As far as I understand a module initialization routine is executed via the
> > sysinit mechanism.  Specifically, module_register_init is set up as the sysinit
> > function for every module and it calls MOD_EVENT(mod, MOD_LOAD) to invoke the
> > module event handler.
> > 
> > In linker_load_file() I see the following code:
> >                          linker_file_register_sysctls(lf);
> >                          linker_file_sysinit(lf);
> > 
> > I think that this means that any statically declared sysctl-s in the module
> > would be registered before the module receives the MOD_LOAD event.
> > It's possible that some of the sysctl-s could have procedures as handlers and
> > they might access data that is supposed to be initialized by the module event
> > handler.
> > 
> > So, for example, running sysctl -a at just the right moment during the loading
> > of a module might end up in an expected behavior (including a crash).
> > 
> > Is my interpretation of how the code works correct?
> > Can the order of linker_file_sysinit and linker_file_register_sysctls be changed
> > without a great risk?
> > 
> > Thank you!
> > 
> > P.S.
> > The same applies to:
> >                  linker_file_sysuninit(file);
> >                  linker_file_unregister_sysctls(file);
> > 
> 
> Hi,
> 
> Not sure if this answers your question.
> 
> If a SYSCTL() is TUNABLE, it's procedure can be called when the sysctl 
> is created. Else the SYSCTL() procedure callback might be called right 
> after it's registered. I think there is an own subsystem in sys/kernel.h 
> which takes care of the actual SYSCTL() creation/destruction - after the 
> linker is involved.

sysctl nodes are created explicitly via linker_file_register_sysctls, not via
SYSINITs, so you can't order them with respect to other init functions.

I think Andriy's suggestion of doing sysctls "inside" sysinits (so they are
registered last and unregistered first) is probably better than the current
state and is a simpler fix than changing all sysctls to use SYSINITs.

-- 
John Baldwin