Re: [PATCH 1/1] uapi: cdc.h: cleanly provide for more interfaces and countries

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Oct 28, 2025 at 03:34:40PM +0100, Oliver Neukum wrote:
> Hi,
> 
> On 28.10.25 14:32, Greg KH wrote:
> > On Tue, Oct 28, 2025 at 01:32:22PM +0100, Oliver Neukum wrote:
> > > The spec requires at least one interface respectively country.
> > > It allows multiple ones. This needs to be clearly said in the UAPI.
> > > 
> > > Signed-off-by: Oliver Neukum <oneukum@suse.com>
> > > ---
> > >   include/uapi/linux/usb/cdc.h | 4 ++--
> > >   1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/uapi/linux/usb/cdc.h b/include/uapi/linux/usb/cdc.h
> > > index 1924cf665448..5fcbce0be133 100644
> > > --- a/include/uapi/linux/usb/cdc.h
> > > +++ b/include/uapi/linux/usb/cdc.h
> > > @@ -105,7 +105,7 @@ struct usb_cdc_union_desc {
> > >   	__u8	bMasterInterface0;
> > >   	__u8	bSlaveInterface0;
> > > -	/* ... and there could be other slave interfaces */
> > > +	__u8	bSlaveInterfaces[];
> > 
> > Can this be combined with bSlaveInterface0?  Feels odd to have 0 and
> > then "more".
> 
> I am afraid the C language does not allow you to specify
> that an array must have a minimum length other than zero.
> In this case bSlaveInterface0 must be present.
> I don't think using only an array would be the right choice.

bSlaveInterface[1] ?

I'll add Gustavo here, he's done lots of work in this area.

> > Also, what determines how many, the overall length?
> 
> bLength - 4 is the number of slave interfaces, which
> must at least be 1.
> We cannot use counted_by in UAPI, can we?

I don't know, Gustavo?

thanks,

greg k-h