uhid(4) and report structures

Marcus von Appen mva at FreeBSD.org
Tue Nov 15 21:04:19 UTC 2011

On, Tue Nov 15, 2011, Alexander Motin wrote:

> On 15.11.2011 21:29, Marcus von Appen wrote:
> > I wonder, if I am correct with my assumption that the usb_ctl_report*
> > structures mentioned in uhid(4) have to be defined and created by the
> > code portion that uses the USB_GET_REPORT(), USB_SET_REPORT(),
> > ... calls.
> >
> > In FreeBSD<  800063 we defined them in the header files of the USB
> > subsystem. After the rewrite those struct definitions vanished.  Will
> > the USB_ macros mentioned in uhid(4) "just" return a byte sequence
> > (that's what I understand from the UHID specification) so that code,
> > which uses those calls, can implement its own struct container for the
> > information retrieved?
> >
> > Thanks for shedding some light on this. In case i am correct with what I
> > wrote above, it might make sense to mention it in uhid(4).
> In new USB stack these calls use struct usb_gen_descriptor argument. 
> Difficult to say why it was done, but it was. To hide that I've recently 
> added two wrapper functions to the libusbhid in HEAD: hid_get_report() 
> and hid_set_report().

So the man page is currently not up to date and can - at least for now -
be assumed to be wrong?
To get the mappings correct, which fields would I have to use from
usb_gen_descriptor? Earlier we had:

struct usb_ctl_report {
    int     ucr_report;
    u_char  ucr_data[1024];

The mapping might be:

    usb_gen_descriptor.ugd_data == usb_ctl_report.ucr_data
    usb_gen_descriptor.ugd_report_type == usb_ctl_report.ucr_report

Is that correct? Also, ugd_data is of variable size with ugd_actlen
indicating the size of the ugd_data buffer?

Best regards
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