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Thu, 8 Oct 2020 07:26:38 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 69E8BF80164; Thu, 8 Oct 2020 07:26:37 +0200 (CEST) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id ACA69F80090 for ; Thu, 8 Oct 2020 07:26:28 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz ACA69F80090 Authentication-Results: alsa1.perex.cz; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="f+IA7WVn" Received: from localhost (unknown [213.57.247.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 48A9320708; Thu, 8 Oct 2020 05:26:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602134787; bh=/KC8SYmVhsAPwhDcSPWxDyKU8idi29YzN2Gwgc8ifro=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=f+IA7WVn+08OlKm0xfQHpXE38NaYkfRfgRqCmIFQ5pOUqAYykcsQhkBx3gvYEkORZ eEVLnmGk4w/6TxxyWGZ/pYsSt/0D0qqJ37S2zyyXdTU0p6I6sPTLLu2gOwsxdVmUp7 V4pmDotAL27lWCvuNpkxWztyvy9BEzi1FMyYEN08= Date: Thu, 8 Oct 2020 08:26:23 +0300 From: Leon Romanovsky To: Parav Pandit Subject: Re: [PATCH v2 1/6] Add ancillary bus support Message-ID: <20201008052623.GB13580@unreal> References: <20201006170241.GM1874917@unreal> <20201007192610.GD3964015@unreal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Cc: "alsa-devel@alsa-project.org" , "kuba@kernel.org" , "parav@mellanox.com" , "tiwai@suse.de" , "netdev@vger.kernel.org" , Pierre-Louis Bossart , "ranjani.sridharan@linux.intel.com" , "fred.oh@linux.intel.com" , "linux-rdma@vger.kernel.org" , "dledford@redhat.com" , "broonie@kernel.org" , Jason Gunthorpe , "gregkh@linuxfoundation.org" , "Ertman, David M" , "Williams, Dan J" , "Saleem, Shiraz" , "davem@davemloft.net" , "Patil, Kiran" X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Thu, Oct 08, 2020 at 04:56:01AM +0000, Parav Pandit wrote: > > > > From: Pierre-Louis Bossart > > 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 > > >> Sent: Wednesday, October 7, 2020 1:59 PM > > >> To: Ertman, David M ; Parav Pandit > > >> ; Leon Romanovsky > > >> Cc: alsa-devel@alsa-project.org; parav@mellanox.com; tiwai@suse.de; > > >> netdev@vger.kernel.org; ranjani.sridharan@linux.intel.com; > > >> fred.oh@linux.intel.com; linux-rdma@vger.kernel.org; > > >> dledford@redhat.com; broonie@kernel.org; Jason Gunthorpe > > >> ; gregkh@linuxfoundation.org; kuba@kernel.org; > > >> Williams, Dan J ; Saleem, Shiraz > > >> ; davem@davemloft.net; Patil, Kiran > > >> > > >> 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