On Fri 2019-05-03 11:16:26, Tobin C. Harding wrote:
> On Thu, May 02, 2019 at 10:34:12AM +0200, Petr Mladek wrote:
> > On Wed 2019-05-01 09:38:03, Tobin C. Harding wrote:
> > I guess that we need two examples. I currently understand
> > it the following way:
> >
> > 1. sysfs interface and the structure can be freed anytime:
> >
> > struct A
> > {
> > struct kobject kobj;
> > ...
> > };
> >
> > void fn(void)
> > {
> > struct A *a;
> > int ret;
> >
> > a = kzalloc(sizeof(*a), GFP_KERNEL);
> > if (!a)
> > return;
> >
> > /*
> > * Initialize structure before we make it accessible via
> > * sysfs.
> > */
> > ret = some_init_fn();
> > if (ret) {
> > goto init_err;
> > }
> >
> > ret = kobject_init_and_add(&a->kobj, ktype, NULL, "foo");
> > if (ret)
> > goto kobj_err;
> >
> > return 0;
> >
> > kobj_err:
> > /* kobject_init() always succeds and take reference. */
> > kobject_put(kobj);
> > return ret;
> >
> > init_err:
> > /* kobject was not initialized, simple free is enough */
> > kfree(a);
> > return ret;
> > }
> >
> >
> > 2. Structure must be registered into the subsystem before
> > it can be made visible via sysfs:
> >
> > struct A
> > {
> > struct kobject kobj;
> > ...
> > };
> >
> > void fn(void)
> > {
> > struct A *a;
> > int ret;
> >
> > a = kzalloc(sizeof(*a), GFP_KERNEL);
> > if (!a)
> > return;
> >
> > ret = some_init_fn();
> > if (ret) {
> > goto init_err;
> > }
> >
> > /*
> > * Structure is in a reasonable state and can be freed
> > * via the kobject release callback.
> > */
> > kobject_init(&a->kobj);
> >
> > /*
> > * Register the structure so that it can cooperate
> > * with the rest of the system.
> > */
> > ret = register_fn(a);
> > ` if (ret)
> > goto register_err;
> >
> >
> > /* Make it visible via sysfs */
> > ret = kobject_add(&a->kobj, ktype, NULL, "foo");
> > if (ret) {
> > goto kobj_add_err;
> > }
> >
> > /* Manipulate the structure somehow */
> > ret = action_fn(a);
> > if (ret)
> > goto action_err;
> >
> > mutex_unlock(&my_mutex);
> > return 0;
> >
> > action_err:
> > /*
> > * Destroy sysfs interface but the structure
> > * is still needed.
> > */
> > kobject_del(&a->kboject);
> > kobject_add_err:
> > /* Make it invisible to the system. */
> > unregister_fn(a);
> > register_err:
> > /* Release the structure unsing the kobject callback */
> > kobject_put(&a->kobj);
> > return;
> >
> > init_err:
> > /*
> > * Custom init failed. Kobject release callback would do
> > * a double free or so. Simple free is enough.
> > */
> > kfree(a);
> > }
> >
> > I would really prefer if we clearly understand where each variant makes
> > sense before we start modifying the code and documentation.
>
> Hi Petr,
>
> Shall we work these two examples into samples/kobject/. I'm AFK now for
> the rest of the week but I can do it on Monday if you don't mind me
> doing it?
Sounds good to me. The current samples/kobject/kobject-example shows
the most simple case when the kobject is standalone. While the
above samples shows how to have it bundled in a bigger structure.
Thanks,
Petr
