Incrementing module reference count

Hi,

I have a kernel module which other modules register with in order to export access functions. So far I have everything working but I want to prevent a module that is registered with my module from unloading since now my module is dependent on the other module.

Is there a way I can cause the reference count of the module registering with my module to increase? I tried calling get_device with the device structure of the module that is registering but that does not seem to work.

For example, I have the following function:

/**
* Adds a mapping of a device node to a memory accessor *
* @param[in] dev - device
* @param[in] macc - memory accessor
*
* @returns 0 for success or -ENOMEM
*/
int of_memory_accessor_register(struct device *dev,
struct memory_accessor *macc)

{
    struct of_macc_entry *mentry;

    mentry = kmalloc(sizeof(*mentry), GFP_KERNEL);
    if (mentry == NULL)
        return -ENOMEM;

    mentry->dev = dev;
    mentry->macc = macc;

    mutex_lock(&lock);

    get_device(dev);
    list_add(&(mentry->list), &macc_list);

    mutex_unlock(&lock);

    return 0;
}

EXPORT_SYMBOL(of_memory_accessor_register);

Basically my module is used for things like serial EEPROMs and whatnot so that external modules can find the accessor functions based on the device tree. In my case I am updating the Vitesse VSC848X driver so that it can read the SFP module when it is plugged in using the AT24 I2C EEPROM module. I want to prevent the at24 module from unloading while other modules in turn are using it. The at24 module does not export any symbols.

From a quick code scan, at24 has this:

Quoted 45 lines · Aaron Williams

Hi,

I have a kernel module which other modules register with in order to export access functions. So far I have everything working but I want to prevent a module that is registered with my module from unloading since now my module is dependent on the other module.

Is there a way I can cause the reference count of the module registering with my module to increase? I tried calling get_device with the device structure of the module that is registering but that does not seem to work.

For example, I have the following function:

/**
* Adds a mapping of a device node to a memory accessor *
* @param[in] dev - device
* @param[in] macc - memory accessor
*
* @returns 0 for success or -ENOMEM
*/
int of_memory_accessor_register(struct device *dev,
struct memory_accessor *macc)

{
    struct of_macc_entry *mentry;

    mentry = kmalloc(sizeof(*mentry), GFP_KERNEL);
    if (mentry == NULL)
        return -ENOMEM;

    mentry->dev = dev;
    mentry->macc = macc;

    mutex_lock(&lock);

    get_device(dev);
    list_add(&(mentry->list), &macc_list);

    mutex_unlock(&lock);

    return 0;
}

EXPORT_SYMBOL(of_memory_accessor_register);

Quoted 7 lines

Basically my module is used for things like serial EEPROMs and whatnot so that external modules can find the accessor functions based on the device tree. In my case I am updating the Vitesse VSC848X driver so that it can read the SFP module when it is plugged in using the AT24 I2C EEPROM module. I want to prevent the at24 module from unloading while other modules in turn are using it. The at24 module does not export any symbols.

From a quick code scan, at24 has this:

	static struct i2c_driver at24_driver = {
	        .driver = {
	                .name = "at24",
	                .owner = THIS_MODULE,
	        },
	        .probe = at24_probe,
	        .remove = __devexit_p(at24_remove),
	        .id_table = at24_ids,
	};

and then you could do:

	try_module_get(at24_driver.driver->owner);

from your code. AFAICT, of course.

HTH.

I got it working. I designed my solution to be generic so it's not tied to just the at24 driver. I added a memory accessor module which is basically a registry. The at24 driver registers with it and then the Vitesse PHY driver calls it to gain access to the at24 driver. Only when the Vitesse driver gets the memory accessor the reference count for the at24 driver is incremented.