On Mon, Jun 12, 2023 at 02:29:05PM +0200, Paolo Bonzini wrote:

On 6/12/23 14:18, Greg KH wrote:

quoted

Yeah, it's a pain, but you are trying to hand-roll code that is not a
"normal" path for a struct device, sorry.

I don't know if you really can encode all of that crazy logic in the
cleanup api, UNLESS you can "switch" the cleanup function at a point in
time (i.e. after device_add() is successful).  Is that possible?

What _could_ make sense is that device_add() completely takes ownership of
the given pointer, and takes care of calling put_device() on failure.

I think we tried that decades ago :)

Problem is that the caller wants to clean stuff up associted with that
struct device-embedded structure _before_ the final put_device() is
called which would usually free the memory of the overall structure.

So device_add() can't call put_device() on the error path within it, you
need the caller to unwind it's local stuff before that happens.

Then you can have

	struct device *dev_struct __free(put_device) =
		kzalloc(sizeof(struct device), GFP_KERNEL);

	struct device *dev __free(device_del) =
		device_add(no_free_ptr(dev_struct));

	/* dev_struct is NULL now */

	pmu->dev = no_free_ptr(dev);

I don't see how that works properly, what am I missing?

thanks,

greg k-h