On Thu, Oct 08, 2020 at 04:56:01AM +0000, Parav Pandit wrote:
>
>
> > From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> > Sent: Thursday, October 8, 2020 3:20 AM
> >
> >
> > On 10/7/20 4:22 PM, Ertman, David M wrote:
> > >> -----Original Message-----
> > >> From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> > >> Sent: Wednesday, October 7, 2020 1:59 PM
> > >> To: Ertman, David M <david.m.ertman@xxxxxxxxx>; Parav Pandit
> > >> <parav@xxxxxxxxxx>; Leon Romanovsky <leon@xxxxxxxxxx>
> > >> Cc: alsa-devel@xxxxxxxxxxxxxxxx; parav@xxxxxxxxxxxx; tiwai@xxxxxxx;
> > >> netdev@xxxxxxxxxxxxxxx; ranjani.sridharan@xxxxxxxxxxxxxxx;
> > >> fred.oh@xxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx;
> > >> dledford@xxxxxxxxxx; broonie@xxxxxxxxxx; Jason Gunthorpe
> > >> <jgg@xxxxxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx; kuba@xxxxxxxxxx;
> > >> Williams, Dan J <dan.j.williams@xxxxxxxxx>; Saleem, Shiraz
> > >> <shiraz.saleem@xxxxxxxxx>; davem@xxxxxxxxxxxxx; Patil, Kiran
> > >> <kiran.patil@xxxxxxxxx>
> > >> Subject: Re: [PATCH v2 1/6] Add ancillary bus support
> > >>
> > >>
> > >>
> > >>>> Below is most simple, intuitive and matching with core APIs for
> > >>>> name and design pattern wise.
> > >>>> init()
> > >>>> {
> > >>>> err = ancillary_device_initialize();
> > >>>> if (err)
> > >>>> return ret;
> > >>>>
> > >>>> err = ancillary_device_add();
> > >>>> if (ret)
> > >>>> goto err_unwind;
> > >>>>
> > >>>> err = some_foo();
> > >>>> if (err)
> > >>>> goto err_foo;
> > >>>> return 0;
> > >>>>
> > >>>> err_foo:
> > >>>> ancillary_device_del(adev);
> > >>>> err_unwind:
> > >>>> ancillary_device_put(adev->dev);
> > >>>> return err;
> > >>>> }
> > >>>>
> > >>>> cleanup()
> > >>>> {
> > >>>> ancillary_device_de(adev);
> > >>>> ancillary_device_put(adev);
> > >>>> /* It is common to have a one wrapper for this as
> > >>>> ancillary_device_unregister().
> > >>>> * This will match with core device_unregister() that has precise
> > >>>> documentation.
> > >>>> * but given fact that init() code need proper error unwinding,
> > >>>> like above,
> > >>>> * it make sense to have two APIs, and no need to export another
> > >>>> symbol for unregister().
> > >>>> * This pattern is very easy to audit and code.
> > >>>> */
> > >>>> }
> > >>>
> > >>> I like this flow +1
> > >>>
> > >>> But ... since the init() function is performing both device_init and
> > >>> device_add - it should probably be called ancillary_device_register,
> > >>> and we are back to a single exported API for both register and
> > >>> unregister.
> > >>
> > >> Kind reminder that we introduced the two functions to allow the
> > >> caller to know if it needed to free memory when initialize() fails,
> > >> and it didn't need to free memory when add() failed since
> > >> put_device() takes care of it. If you have a single init() function
> > >> it's impossible to know which behavior to select on error.
> > >>
> > >> I also have a case with SoundWire where it's nice to first
> > >> initialize, then set some data and then add.
> > >>
> > >
> > > The flow as outlined by Parav above does an initialize as the first
> > > step, so every error path out of the function has to do a
> > > put_device(), so you would never need to manually free the memory in
> > the setup function.
> > > It would be freed in the release call.
> >
> > err = ancillary_device_initialize();
> > if (err)
> > return ret;
> >
> > where is the put_device() here? if the release function does any sort of
> > kfree, then you'd need to do it manually in this case.
> Since device_initialize() failed, put_device() cannot be done here.
> So yes, pseudo code should have shown,
> if (err) {
> kfree(adev);
> return err;
> }
>
> If we just want to follow register(), unregister() pattern,
>
> Than,
>
> ancillar_device_register() should be,
>
> /**
> * ancillar_device_register() - register an ancillary device
> * NOTE: __never directly free @adev after calling this function, even if it returned
> * an error. Always use ancillary_device_put() to give up the reference initialized by this function.
> * This note matches with the core and caller knows exactly what to be done.
> */
> ancillary_device_register()
> {
> device_initialize(&adev->dev);
> if (!dev->parent || !adev->name)
> return -EINVAL;
> if (!dev->release && !(dev->type && dev->type->release)) {
> /* core is already capable and throws the warning when release callback is not set.
> * It is done at drivers/base/core.c:1798.
> * For NULL release it says, "does not have a release() function, it is broken and must be fixed"
> */
> return -EINVAL;
> }
> err = dev_set_name(adev...);
> if (err) {
> /* kobject_release() -> kobject_cleanup() are capable to detect if name is set/ not set
> * and free the const if it was set.
> */
> return err;
> }
> err = device_add(&adev->dev);
> If (err)
> return err;
> }
>
> Caller code:
> init()
> {
> adev = kzalloc(sizeof(*foo_adev)..);
> if (!adev)
> return -ENOMEM;
> err = ancillary_device_register(&adev);
> if (err)
> goto err;
>
> err:
> ancillary_device_put(&adev);
> return err;
> }
>
> cleanup()
> {
> ancillary_device_unregister(&adev);
> }
>
> Above pattern is fine too matching the core.
>
> If I understand Leon correctly, he prefers simple register(), unregister() pattern.
> If, so it should be explicit register(), unregister() API.
This is my summary
https://lore.kernel.org/linux-rdma/20201008052137.GA13580@unreal
The API should be symmetric.
Thanks
