Cornelia Huck wrote: > On Fri, 30 Mar 2007 22:58:39 +0900, > Tejun Heo <[EMAIL PROTECTED]> wrote: > >> It's a little bit more convoluted than that. Module reference count of >> zero doesn't indicate that there is no one referencing the module. It >> just means that the module can be unloaded. ie. There still can be any >> number of kobjects with release function backed by the module but as >> long as all of them can be deleted and released by module exit function, >> the module is unloadable at that point. >> >> IOW, module reference count does not count number of objects depending >> on the module. It counts the number of active usages of those objects. > > We must make sure that the module is never deleted while there may be > calls to ->release functions - the exit function can only return when > all ->release calls have returned. This can be guaranteed if we (1) > don't allow the module to unload if there are outstanding kobjects (we > may need a "self destruct" knob then) or (2) make sure the ->release > functions are outside of the module (see, for example, > drivers/s390/s390_rdev.c).
(3) make sure all existing kobjects are released by module exit function. For example, let's say there is a hypothetical disk device /dev/dk0 driven by a hypothetical driver mydrv. /dev/dk0 is represented like the following in the sysfs tree. /sys/devices/pci0000:00/0000:00:1f.0/dk0/{myknob0,myknob1} Owner of both attrs myknob0 and myknob1 is mydrv and opening either increases the reference counts of dk0 and mydrv and closing does the opposite. * When there is no opener of either knob and the /dev/dk0 isn't used by anyone. Reference count of dk0 is 1, mydrv 0. * User issues rmmod mydrv. As mydrv's reference count is zero, unload proceeds and mydrv's exit function is called. * mydrv's exit function looks like the following. mydrv_exit() { sysfs_remove_file(dk0, myknob0); sysfs_remove_file(dk1, myknob1); device_del(dk0); deinit controller; release all resources; } The device_del(dk0) drops dk0's reference count to zero and its ->release is invoked immediately. This method is widely used to allow modules to be unloaded even when there still are valid objects if there's no active user. > (Gah, that stuff is always giving me headaches. Sorry if I'm not making > sense...) Yeap, this is confusing. Hope my explanation makes sense. -- tejun - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html