Re: [RFC] kobject: add kobject_init_ng and kobject_init_and_add functions

On Fri, Nov 30, 2007 at 05:10:33PM -0500, Alan Stern wrote:
On Fri, 30 Nov 2007, Greg KH wrote:

Ok, how about this:
void kobject_init(struct kobject *kobj, struct ktype *ktype);

and then:
int kobject_add(struct kobject *kobj, struct kobject *parent, const char *fmt, ...);

After we call kobject_init() we HAVE to call kobject_put() to clean up
properly. So, if kobject_add() fails, we still need to clean up with
kobject_put();

You could put that a little less strongly. After kobject_init() you
SHOULD call kobject_put() to clean up properly, and after kobject_add()
you MUST call kobject_del() and kobject_put().

However if kobject_add() is never called, or if it is called and it
fails, then it's okay to use kfree(). It's not clear whether this
distinction will matter in practice. It's probably best to document
this using your stronger description.

No, if kobject_add() fails, kobject_put() still must be called in order
to free up the name pointer, unless you are somehow guessing that the
"kobject_set_name()" portion of kobject_add() somehow failed. And you
can't know that, so you have to call kobject_put() in order to be safe
and clean up everything.

Now why did we not do the final kobject_put() in kobject_del() as well?
Doing two calls, always in order, seems a bit strange, anyone know why
it's this way?

The same sort of rule should apply to other kernel objects, like struct
device. After intialization you have to do a final _put, before that
you just do a kfree(). (And initialization cannot fail.)

Yes.

That means we _can_ create a:
int kobject_init_and_add(struct kobject *kobj, struct ktype *ktype, struct kobject *parent, const char *fmt, ...);

and if that fails, then again, you have to call kobject_put() to clean
things up, right?

Right. Because you know that the failure must have occurred in the
_add portion.

Ok, good, I might get this right yet :)

thanks,

greg k-h
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