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 n0FFYOeq023204 for ; Thu, 15 Jan 2009 10:34:24 -0500 Received: from dd18532.kasserver.com (dd18532.kasserver.com [85.13.139.13]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id n0FFXofa015471 for ; Thu, 15 Jan 2009 10:33:50 -0500 Date: Thu, 15 Jan 2009 16:33:48 +0100 From: Carsten Meier To: "Markus Rechberger" Message-ID: <20090115163348.5da9932a@tuvok> In-Reply-To: References: <20090115154111.36cc25d1@tuvok> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: video4linux-list@redhat.com Subject: Re: How to identify USB-video-devices 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: Am Thu, 15 Jan 2009 16:20:23 +0100 schrieb "Markus Rechberger" : > On Thu, Jan 15, 2009 at 3:41 PM, Carsten Meier wrote: > > Hello list, > > > > we recently had a discussion on the pvrusb2-list on how to identify > > a video-device connected via USB from an userspace app. (Or more > > precisely on how to associate config-data with a particular > > device). This led to a patch which returned the device's serial-no. > > in v4l2_capability's bus_info field. This one has been rejected, > > but I really feel that this is the right way to go. Here's the > > thread: > > http://www.isely.net/pipermail/pvrusb2/2009-January/002091.html > > > > I think the meaning of the bus_info-field should be modified > > slightly for USB-devices to reflect its dynamic nature. At least a > > string that won't change on dis-/reconnect and > > standby/wake-up-cycles should be returned. If a device has a unique > > serial-no. it is a perfect candidate for this, if not, some > > USB-port-info should be returned that won't change if the device is > > connected to the same port through the same hub. > > > > What do you think? > > (BTW: I'm not a kernel-hacker, I'm writing this from the > > perspective of an app-developer) > > > > write a few shellscripts and parse sysfs, or attach your application > to sysfs that it will > be notified if a device gets added. dbus is also a tip. no need to > hook up drivers > with some special things there. > > regards, > Markus But according to the docs, the bus_info-field is intended for the purpose of identifying particular devices. Other solutions may be possible, but they are much more complex and much more sensible to other kernel-changes. By using bus_info, there is a simple and clean solution that only depends on the V4L2-API and it also reflects the primary intention of the field. Other USB-device-drivers aren't required to change to the new policy, their current bus_info-string (if implemented like in pvrusb2) changes on every reconnect and standby/wake-up-cycle and is of no use anyway for any app. I really think that current behaviour is broken. Regards, Carsten -- video4linux-list mailing list Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe https://www.redhat.com/mailman/listinfo/video4linux-list