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

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.

--HPS