Re: [PATCH] release_resource() check for NULL resource

[Pekka Enberg <penberg@cs.helsinki.fi>]

On 10/3/05, Russell King <rmk+lkml@arm.linux.org.uk> wrote:
> It makes sense for kfree() to ignore NULL pointers, but does it really
> make sense for *_unregister() to do so too?  Surely you want to only
> unregister things which you know have previously been registered?

Usually yes but it makes releasing partial initialization much simpler
because you can  reuse the normal release counterpart. For example,

static int driver_init(void)
{
     dev->resource1 = request_region(...);
     if (!dev->resource1)
             goto failed;

     dev->resource2 = request_region(...);
     if (!dev->resource2)
             goto failed;

     return 0;

failed:
     driver_release(dev);
     return -1;
}

static void driver_release(struct device * dev)
{
     release_resource(dev->resource1);
     release_resource(dev->resource2);
     kfree(dev);
}

Many drivers have the release function copy-pasted to init with lots
of goto labels exactly because release_region, iounmap, and friends
aren't NULL safe.

                                       Pekka