From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id mAJ9ZL9s000858 for ; Wed, 19 Nov 2008 04:35:21 -0500 Received: from smtp4.versatel.nl (smtp4.versatel.nl [62.58.50.91]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id mAJ9Z8kx012977 for ; Wed, 19 Nov 2008 04:35:08 -0500 Message-ID: <4923DF13.4090609@hhs.nl> Date: Wed, 19 Nov 2008 10:40:35 +0100 From: Hans de Goede MIME-Version: 1.0 To: Linux and Kernel Video Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Cc: Elmar Kleijn , "radjnies@gmail.com" , =?windows-1252?Q?Luk=E1=9A_Karas?= , "need4weed@gmail.com" Subject: RFC: add emulated controls to libv4l List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: video4linux-list-bounces@redhat.com Errors-To: video4linux-list-bounces@redhat.com List-ID: Hi all, As discussed in my previous mail, various people (including me) want to add things like software whitebalancing, etc. to libv4l. When this is added, it would be nice for the user to be able to control this (turn on/off) using a standard v4l control panel application as for example v4l2ucp. The question I want to discuss here is how to implement this. We want this to work as much as possible as real controls, so: -Settings can be changed by one app (control panel), influencing the picture seen by another app which is streaming -Settings are remembered even when no app has the device open -Settings are reset acros a driver unload / load (typically a reboot) There are 3 possible solutions here: 1) Add an API to the driver to store and retreive "fake" settings 2) Use shared memory 3) Use shared memory by creating shared memory mappings of a (binary) file So which one to use 1) Has the advantage of the resulting behavior matching that of real controls exactly, but requires adding code to the kernel, lets no do that. 2) IIRC it is possible to keep a shared memory segment around (until reboot) even if no app is using it, this will then pretty closely match the behavior of normal controls. Also Lukáš Karas has already submitted a patch implementing this, which is a pre too :) 3) This is only usefull if it turns out to not be possible to keep a shared memory segment around even if no app is using it. This has the disadvantage of keeping settings even across reboots, which could be seen as an advantage, but if we want to do this (which I believe we do) we should write an utility program to do this. So my vote clearly goes to option 2, what do others here on the list think? Regards, Hans -- video4linux-list mailing list Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe https://www.redhat.com/mailman/listinfo/video4linux-list