Linux Kernel: how to use request_module() and try_module_get()

Question

I'm struggling to understand how to use in the proper way the

try_module_get()

I found this interesting post: How to put a check in the code to ensure the inter kernel module dependency - Linux Kernel?

But I miss one point: I can get the request_module working, but I don' get how to use the try_module_get

I explain:

If I use

ret = request_module("ipt_conntrack")

the module xt_conntrack is correctly inserted, but marked as no used, because accordingly to the above post I didn't used the try_module_get.

But how can I call the try_module_get? The function requires a struct module parameter, which I don't know how to populate for the xt_conntrack module. I found several examples, but all related to the "THIS_MODULE" parameter, which does not apply in this case. Can you point me in the right direction for this?

Thanks for your help

Answer 1

Perhaps something like this would work. I haven't tested it.

/**
 * try_find_module_get() - Try and get reference to named module
 * @name: Name of module
 *
 * Attempt to find the named module.  If not found, attempt to request the module by
 * name and try to find it again.  If the module is found (possibly after requesting the
 * module), try and get a reference to it.
 *
 * Return:
 * * pointer to module if found and got a reference.
 * * NULL if module not found or failed to get a reference.
 */
static struct module *try_find_module_get(const char *name)
{
    struct module *mod;

    mutex_lock(&module_mutex);
    /* Try and find the module. */
    mod = find_module(name);
    if (!mod) {
        mutex_unlock(&module_mutex);
        /* Not found.  Try and request it. */
        if (request_module(name))
            return NULL;  /* Failed to request module. */
        mutex_lock(&module_mutex);
        /* Module requested.  Try and find it again. */
        mod = find_module(name);
    }
    /* Try and get a reference if module found. */
    if (mod && !try_module_get(mod))
        mod = NULL;  /* Failed to get a reference. */
    mutex_unlock(&module_mutex);
    return mod;
}