Re: Handling incoming ZLP in cdc-wdm

[Oliver Neukum <oneukum@suse.com>]

(Adding Bjørn)

On 27.03.25 16:27, Robert Hodaszi wrote:
> On Thursday, 27.03.2025 at 14:24 +0100, Oliver Neukum <oneukum@suse.com> wrote:
>>
>> Why do you wish to react to this like an error?
>> It seems to me that we indeed need to wait for the device in this case.
>>
>>         Regards
>>                 Oliver
>>
> See my previous response to your patch. Because:
> 
>      1. we have to submit another read URB is resp_count != 0 (call service_outstanding_interrupt), otherwise receiving gets stuck

Now that you mention that I am not sure that the resp_count
logic in general is correct. I see no reason user space cannot
exhaust the buffer and get resp_count out of sync.

>      2. we should not set WDM_READ, to not confuse userspace

We agree on that.

>      3. we should not set res_length to 0, otherwise  we get stuck again (actually, should we clear the "if (!desc->reslength)" in wdm_read(), since that's is no longer possible anymore?

AFAICT it can happen if two threads are racing on wdm_read()

	Regards
		Oliver