Date: Wed, 2 Aug 2017 12:39:36 +0200 From: Hans Petter Selasky <hps@selasky.org> To: Andriy Gapon <avg@FreeBSD.org>, FreeBSD Hackers <freebsd-hackers@FreeBSD.org>, FreeBSD Current <freebsd-current@FreeBSD.org> Subject: Re: order of executing MOD_LOAD and registering module sysctl-s Message-ID: <c73441ae-e623-3828-d10e-74947c78240b@selasky.org> In-Reply-To: <62e7ab4d-8956-545e-b204-4fb63cfe5fbf@FreeBSD.org> References: <62e7ab4d-8956-545e-b204-4fb63cfe5fbf@FreeBSD.org>
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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. --HPShelp
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