cpufreq: mediatek: allow modular build

Russell King - ARM Linux
2015-09-11T10:13:41Z

On Fri, Sep 11, 2015 at 03:39:16PM +0530, Viresh Kumar wrote:
> On 11-09-15, 10:58, Russell King - ARM Linux wrote:
> > Not module "unplug" (I've never heard it called that before). A module
> > with a module_init() but no module_exit() can only be added to a running
> > kernel, and never removed. That's intentional behaviour.
>
> Ah, I see. I wasn't sure that a module with no module_exit() can't be
> removed.

Yes, but it's not that simple.

A module with no module_init() and no module_exit() is what's called a
library module, which can be inserted, and later removed provided no
other module depends on anything the library module exports.

A module with a module_init() but no module_exit() is one which can be
inserted, but never removed.

A module with a module_init() and a module_exit() can be inserted, and
later removed in much the same way as the library module mentioned above.

See kernel/module.c:

/* If it has an init func, it must have an exit func to unload */
if (mod->init && !mod->exit) {
forced = try_force_unload(flags);
if (!forced) {
/* This module can't be removed */
ret = -EBUSY;
goto out;
}
}

and

if (mod->init != NULL && mod->exit == NULL) {
printed_something = 1;
seq_puts(m, "[permanent],");
}

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