usb/137189: [usb][patch] create and use sysctl nodes for HID report descriptors

Eygene Ryabinkin rea-fbsd at
Tue Jul 28 15:50:04 UTC 2009

The following reply was made to PR usb/137189; it has been noted by GNATS.

From: Eygene Ryabinkin <rea-fbsd at>
To: bug-followup at, freebsd-usb at
Cc: hselasky at
Subject: Re: usb/137189: [usb][patch] create and use sysctl nodes for HID
 report descriptors
Date: Tue, 28 Jul 2009 19:40:27 +0400

 HPS wrote:
 > > I can, but how to relate the device name under devfs to the descriptor
 > > to be retrieved?
 > By unit number and device address, like usbconfig.
 Yes, but these numbers are the ugen ones; on my system, for example,
 ums0 maps to ugen5.3.0.
 >>  I can enumerate all HID descriptors via libusb, but I
 > > can't currently say which device uses them.
 > Try:
 > usbconfig show_ifdrv
 Yes, that's better.  But can I rely that the first item in the output of
 the libusb20_dev_get_iface_desc() will be the device name?  And still,
 to get the report descriptor from one device, I should walk the entire
 USB tree until I'll find the device I am interested in.  May be there
 are some other ways?  I understand that enumeration is the principle of
 the USB bus, but may be there are another ways to directly grab 'struct
 libusb20_device *' or alike for the devfs node I am interested in?
 > > Why do you dislike the sysctl approach? It is simple and reliable.
 > It's duplicating access to data. There is not that much wrong about
 > it, except it will not work if the device is of another kind. I.E. you
 > would have to patch the HID sysctl node into every driver accessing
 > HID descriptors?
 Just now -- yes, I'll need it.  But probably I can move this
 functionality into the USB bus level -- it will automatically create
 this sysctl node for all HID children and will dispose it on the detach.
 usb_probe_and_attach() is a candidate for such functionality.  Will it
 be bad?
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