Freeing a dynamic struct cdev

Freeing a dynamic struct cdev

[James C. Georgas]

If I allocate a struct cdev using cdev_alloc(), what function do I call
to free it when I'm done with it?

-- 
James C. Georgas <jgeorgas@rogers.com>

Re: Freeing a dynamic struct cdev

[Randy.Dunlap]

On Sat, 06 Aug 2005 09:26:15 -0400 James C. Georgas wrote:

> If I allocate a struct cdev using cdev_alloc(), what function do I call
> to free it when I'm done with it?

Should be cdev_put(), which calls kobject_put(), which implements
ref counting (using krefs), so that when the last reference is
going away, the object will be removed.

---
~Randy

Re: Freeing a dynamic struct cdev

[James C. Georgas]

On Sat, 2005-08-06 at 12:21 -0700, Randy.Dunlap wrote:
> On Sat, 06 Aug 2005 09:26:15 -0400 James C. Georgas wrote:
> 
> > If I allocate a struct cdev using cdev_alloc(), what function do I call
> > to free it when I'm done with it?
> 
> Should be cdev_put(), which calls kobject_put(), which implements
> ref counting (using krefs), so that when the last reference is
> going away, the object will be removed.
> 
> ---
> ~Randy

cdev_put() is not an exported symbol in the fs/char_dev.c file. Should
it be?
-- 
James C. Georgas <jgeorgas@rogers.com>

Re: Freeing a dynamic struct cdev

[Randy.Dunlap]

On Sat, 06 Aug 2005 15:26:18 -0400 James C. Georgas wrote:

> On Sat, 2005-08-06 at 12:21 -0700, Randy.Dunlap wrote:
> > On Sat, 06 Aug 2005 09:26:15 -0400 James C. Georgas wrote:
> > 
> > > If I allocate a struct cdev using cdev_alloc(), what function do I call
> > > to free it when I'm done with it?
> > 
> > Should be cdev_put(), which calls kobject_put(), which implements
> > ref counting (using krefs), so that when the last reference is
> > going away, the object will be removed.
> > 
> > ---
> > ~Randy
> 
> cdev_put() is not an exported symbol in the fs/char_dev.c file. Should
> it be?

Sorry about that, typo on my part.  It's cdev_del().

---
~Randy

Re: Freeing a dynamic struct cdev

[James C. Georgas]

Ok, I really blew it with that last post:

> 
> cdev_add() calls:
> 	kobj_map()
> 	kobject_get() [indirectly]
> 

This is wrong. When I first looked at it, I saw:

cdev_add() -> kobj_map() -> exact_lock() -> cdev_get() -> kobject_get()

but exact_lock() isn't called here; it is only passed as a function
pointer to kobj_map(), and so calling cdev_add() does /not/ increment
the reference count of the struct cdev.

I guess what threw me for a loop here was that I was expecting separate
functions: one to undo cdev_add() and one to undo cdev_alloc(), but
cdev_del() accomplishes both tasks in one function, with the
kobj_unmap() part having no effect, if the cdev is not mapped at the
time of the call.

-- 
James C. Georgas <jgeorgas@rogers.com>