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

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Date:   Wed, 7 Oct 2020 16:49:57 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
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" <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



On 10/7/20 4:22 PM, Ertman, David M wrote:
>> -----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.

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.