From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Sakamoto Subject: Re: Some questions about userspace control elements Date: Mon, 02 Feb 2015 23:14:39 +0900 Message-ID: <54CF864F.8060208@sakamocchi.jp> References: <54CE10D2.7090903@sakamocchi.jp> <54CE675A.80004@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp302.phy.lolipop.jp (smtp302.phy.lolipop.jp [210.157.22.85]) by alsa0.perex.cz (Postfix) with ESMTP id D0DC8260614 for ; Mon, 2 Feb 2015 15:14:45 +0100 (CET) In-Reply-To: <54CE675A.80004@ladisch.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Clemens Ladisch , "alsa-devel@alsa-project.org" List-Id: alsa-devel@alsa-project.org Hi Clemens, Thanks for your answer. I want to discuss about the design of ALSA userspace controls with you, while today I've read some related kernel codes and realized they're more buggy than I expected...perhaps. I'd like to start discussion after fixing them. Thanks Takashi Sakamoto On Feb 2 2015 02:50, Clemens Ladisch wrote: > Takashi Sakamoto wrote: >> 1.The 'numid' is unique number for each element or not? >> I want to use it to indicate each element, if possible. But there're >> more members in snd_ctl_elem_id structure. > > The other members help with searching elements. But numid itself must > be unique. > >> 2.The 'numid' can be notified in SND_CTL_EVENT_MASK_ADD event? >> As long as I test, it's always zero when userspace applications add any >> elements. Is it an expected behaviour? Or a bug? > > This looks like a bug in the kernel code. > > All the other members of the id structure should be correct; as > a workaround, try calling snd_ctl_elem_info(). > >> 3.The way to change permissions of each control element. >> Is it possible after adding the elements? If possible, how to notify it >> in the other processes? > > At the moment, this is not possible for userspace controls. > > What bit(s) do you want to change? > >> 4.Any elements added by a process are not removed at closing snd_ctl_t. >> They're remained after closing the process' snd_ctl_t. Is it an expected >> behaviour? Or a bug? > > This is by design. These controls are intended to be a property of the > device itself, and to be somewhat permanent. > >> 5.Processes can delete elements which the other processes added. >> Is it an expected behaviour? Or a bug? > > For permanent controls, it would not be possible to remember which > process created them originally. > >> 6.The operation to replace elements generates separate events. >> ADD/REMOVE events occurs sequencially. Userspace application cannot >> distinguish replacement from adding/removing, therefore cannot process >> appropriate action. Is it an expected behaviour? Or a bug? > > Replacement is just a shortcut for removing/adding. So far, changing > the properties of userspace controls has not been necessary. > > > Regards, > Clemens