Re: [PATCH 2/2] HID: logitech-hidpp: store the name of the device in struct hidpp

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

On Dec 17 2014 or thereabouts, Peter Wu wrote:
> On Tuesday 16 December 2014 17:06:02 Benjamin Tissoires wrote:
> > If a disconnect occurs while getting the actual name of the device
> > (which can take several HID transactions), the name of the device will
> > be the hid name, provided by the Unifying Receiver.
> > This means that in some cases, the user space will see a different
> > name that what it usually sees when there is no disconnect.
> > 
> > We should store the name of the device in the struct hidpp. That way,
> > if a disconnect occurs while we are accessing the name,
> > hidpp_connect_event() can fail, and the input node is not created.
> > 
> > The input node will be created only if we have a connection which
> > lasts long enough to retrieve all the requested information:
> > name, protocol, and specific configuration.
> > 
> > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > ---
> >  drivers/hid/hid-logitech-hidpp.c | 31 ++++++++++++++++++++-----------
> >  1 file changed, 20 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> > index c0fb5fe..4bc8714 100644
> > --- a/drivers/hid/hid-logitech-hidpp.c
> > +++ b/drivers/hid/hid-logitech-hidpp.c
> > @@ -89,6 +89,7 @@ struct hidpp_device {
> >  	struct hid_device *hid_dev;
> >  	struct mutex send_mutex;
> >  	void *send_receive_buf;
> > +	char *name;
> >  	wait_queue_head_t wait;
> >  	bool answer_available;
> >  	u8 protocol_major;
> > @@ -1087,6 +1088,7 @@ static void hidpp_input_close(struct input_dev *dev)
> >  static struct input_dev *hidpp_allocate_input(struct hid_device *hdev)
> >  {
> >  	struct input_dev *input_dev = devm_input_allocate_device(&hdev->dev);
> > +	struct hidpp_device *hidpp = hid_get_drvdata(hdev);
> >  
> >  	if (!input_dev)
> >  		return NULL;
> > @@ -1095,7 +1097,7 @@ static struct input_dev *hidpp_allocate_input(struct hid_device *hdev)
> >  	input_dev->open = hidpp_input_open;
> >  	input_dev->close = hidpp_input_close;
> >  
> > -	input_dev->name = hdev->name;
> > +	input_dev->name = hidpp->name;
> >  	input_dev->phys = hdev->phys;
> >  	input_dev->uniq = hdev->uniq;
> >  	input_dev->id.bustype = hdev->bus;
> > @@ -1137,22 +1139,28 @@ static void hidpp_connect_event(struct hidpp_device *hidpp)
> >  	hid_info(hdev, "HID++ %u.%u device connected.\n",
> >  		 hidpp->protocol_major, hidpp->protocol_minor);
> >  
> > +	if (!hidpp->name || hidpp->name == hdev->name) {
> 
> Hm, is it ever possible that hidpp->name is NULL? probe sets the pointer

No, hidpp->name should never be a NULL reference.
I asked myself about that (i.e. having a NULL reference until the hidpp
calls get_name), but I thought that having a non consistent name would
just confuse other contributors when implementing other devices.
So I choose to have always the current name of the device.

> to an array (hdev->name). Defence in depth I guess, but perhaps a
> comment could clarify this?

That could clarify it, yes. Will send a v2.

> 
> Otherwise the changes look OK. I have tested this situation:
> 
>  1. Insert receiver
>  2. Return a HID++ version for the WTP.
>  3. Return -9 (ResourceError) for the device name feature request (via
>     the QEMU emulation).
>  4. Observe that this fails.

Hehe, I have been testing this by timely putting the device in the on
then off state. About 1 sec of ON is enough to trigger the various
failures :)

> 
> So maybe you could add a comment for the above and add these tags:
> 
> Reviewed-by: Peter Wu <peter@lekensteyn.nl>
> Tested-by: Peter Wu <peter@lekensteyn.nl>

Thanks! (and thanks for the other v3)

Cheers,
Benjamin

> 
> Kind regards,
> Peter
> 
> > +		name = hidpp_get_device_name(hidpp);
> > +		if (!name) {
> > +			hid_err(hdev,
> > +				"unable to retrieve the name of the device");
> > +			return;
> > +		}
> > +
> > +		devm_name = devm_kasprintf(&hdev->dev, GFP_KERNEL, "%s", name);
> > +		kfree(name);
> > +		if (!devm_name)
> > +			return;
> > +
> > +		hidpp->name = devm_name;
> > +	}
> > +
> >  	input = hidpp_allocate_input(hdev);
> >  	if (!input) {
> >  		hid_err(hdev, "cannot allocate new input device: %d\n", ret);
> >  		return;
> >  	}
> >  
> > -	name = hidpp_get_device_name(hidpp);
> > -	if (!name) {
> > -		hid_err(hdev, "unable to retrieve the name of the device");
> > -	} else {
> > -		devm_name = devm_kasprintf(&hdev->dev, GFP_KERNEL, "%s", name);
> > -		if (devm_name)
> > -			input->name = devm_name;
> > -		kfree(name);
> > -	}
> > -
> >  	hidpp_populate_input(hidpp, input, false);
> >  
> >  	ret = input_register_device(input);
> > @@ -1175,6 +1183,7 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
> >  		return -ENOMEM;
> >  
> >  	hidpp->hid_dev = hdev;
> > +	hidpp->name = hdev->name;
> >  	hid_set_drvdata(hdev, hidpp);
> >  
> >  	hidpp->quirks = id->driver_data;
> > 
>