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List:       linux-usb-devel
Subject:    Re: [linux-usb-devel] Identify /dev by USB topological location?
From:       Tim Jansen <tim () tjansen ! de>
Date:       2001-02-22 20:41:08
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On Wed, Feb 21, 2001 at 02:00:34PM -0800, David Brownell wrote:
> Most of the "enum device_interface" entries would seem to duplicate
> the {char/bulk, dev_t } tuple semantics.  To use your example,
> V4L has assigned codes there ... if a tool can see that the driver has
> exposed some device ids in the V4L range, that's good enough.
> Plus, we already have Documentation/devices.txt; it seems unwise to
> (partially) mirror its functionality.  Replacing it would be another issue;

For me it seems unwise that an user-space app should contain a database that
maps dev_t's on interfaces, it binds you to those drivers that are
contained in a particular kernel version.

Major/Minor numbers can change between kernel versions (thats why we use files 
to access them), and they can not contain the numbers of those drivers that 
are not in the kernel. Take the psaux interface as an example. Currently 
/dev/psaux has the device number 10/1 and the /dev/input/mouseX devices have 
13/32+x. If a hardware manufacturer releases a pointing device that does not 
use the HID class you would have another major/minor range, but the 
user-space app cannot know it. You would have to extend it for every
available driver. 

bye...




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