On Fri, Mar 26, 2021 at 09:10:48AM -0300, Jason Gunthorpe wrote:

It is usually hidden and works like this:

 /* pci_register_driver() must be a macro so KBUILD_MODNAME can be expanded */
 #define pci_register_driver(driver)		\
 	__pci_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
 
 int __pci_register_driver(struct pci_driver *drv, struct module *owner,
 			  const char *mod_name)
 {
	drv->driver.owner = owner;
  	drv->driver.mod_name = mod_name;

Indeed, there seem to be about two handful of instance of that.

quoted

I've not really seen that in anywere else, and the only user seems
to be module_add_driver for a rather odd case we shouldn't hit here.

vfio_mdev could be compiled built in? 

AFAICT it handles the case where THIS_MODULE==NULL so we still need to
create sysfs links to the built in module.

If it is left NULL then a few sysfs files go missing for the built in
mode but no harm done?

Yes, it seems to be needed for a few driver-specific files.  So it looks
ok, even if rather unexpected.