netdev - RE: [PATCH v2 1/6] Add ancillary bus support

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Date:   Wed, 7 Oct 2020 21:22:29 +0000
From:   "Ertman, David M" <david.m.ertman@...el.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Parav Pandit <parav@...dia.com>,
        Leon Romanovsky <leon@...nel.org>
CC:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "tiwai@...e.de" <tiwai@...e.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ranjani.sridharan@...ux.intel.com" 
        <ranjani.sridharan@...ux.intel.com>,
        "fred.oh@...ux.intel.com" <fred.oh@...ux.intel.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Saleem, Shiraz" <shiraz.saleem@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "Patil, Kiran" <kiran.patil@...el.com>
Subject: RE: [PATCH v2 1/6] Add ancillary bus support

> -----Original Message-----
> From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> Sent: Wednesday, October 7, 2020 1:59 PM
> To: Ertman, David M <david.m.ertman@...el.com>; Parav Pandit
> <parav@...dia.com>; Leon Romanovsky <leon@...nel.org>
> Cc: alsa-devel@...a-project.org; parav@...lanox.com; tiwai@...e.de;
> netdev@...r.kernel.org; ranjani.sridharan@...ux.intel.com;
> fred.oh@...ux.intel.com; linux-rdma@...r.kernel.org;
> dledford@...hat.com; broonie@...nel.org; Jason Gunthorpe
> <jgg@...dia.com>; gregkh@...uxfoundation.org; kuba@...nel.org; Williams,
> Dan J <dan.j.williams@...el.com>; Saleem, Shiraz
> <shiraz.saleem@...el.com>; davem@...emloft.net; Patil, Kiran
> <kiran.patil@...el.com>
> 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.

-DaveE

> >
> > At that point, do we need wrappers on the primitives init, add, del,
> > and put?
> >
> > -DaveE
> >