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

[Oliver Neukum <oneukum@suse.com>]

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.
> 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?

	Regards
		Oliver