Re: [PATCH] usb: gadget: f_mass_storage: Shut down mass storage device when USB connection is shut, down.

[Florian Faber <faber@faberman.de>]

On 9/4/21 6:09 PM, Alan Stern wrote:
> On Sat, Sep 04, 2021 at 05:32:58PM +0200, Florian Faber wrote:
>> f_mass_storage continues to send out packets after the connection to the USB
>> host has been terminated, ignoring the error status.
> 
> The driver doesn't send packets after the connection has been terminated --
> that would be impossible.  It may _try_ to send packets, but it can't
> actually send anything unless the hosts asks for the data.  There's nothing
> wrong with trying and failing.

Correct, that could have been expressed more clearly.

> 
>> Signed-off-by: Florian Faber <faber@faberman.de>
>>
>> ---
>>   drivers/usb/gadget/function/f_mass_storage.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/function/f_mass_storage.c
>> b/drivers/usb/gadget/function/f_mass_storage.c
>> index 6ad669dde41c..1e73ba629e43 100644
>> --- a/drivers/usb/gadget/function/f_mass_storage.c
>> +++ b/drivers/usb/gadget/function/f_mass_storage.c
>> @@ -529,6 +529,10 @@ static int start_transfer(struct fsg_dev *fsg, struct
>> usb_ep *ep,
>>   		/* We can't do much more than wait for a reset */
>>   		req->status = rc;
>>
>> +		if (rc==-ESHUTDOWN) {
>> +			fsg->common->running = 0;
>> +		}
>> +
> 
> This is wrong because it isn't what common->running means.  common->running
> means that the mass-storage configuration has been set by the host; it has
> nothing to do with whether or not the USB cable is connected.

So it is OK to keep the thread running and _trying_ to send out packets 
all the time until another USB host is plugged in, wasting resources?

I would argue that the removal of a USB host is an implicit 
configuration change.


Flo
-- 
Machines can do the work, so people have time to think.