linux-kernel - Re: [PATCH v2] HID: logitech-hidpp: store the name of the device in struct hidpp

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Date:	Thu, 08 Jan 2015 23:36:39 +0100
From:	Peter Wu <peter@...ensteyn.nl>
To:	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:	Jiri Kosina <jkosina@...e.cz>,
	Nestor Lopez Casado <nlopezcasad@...itech.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] HID: logitech-hidpp: store the name of the device in struct hidpp

On Thursday 08 January 2015 14:37:12 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.
> 
> Reviewed-by: Peter Wu <peter@...ensteyn.nl>
> Tested-by: Peter Wu <peter@...ensteyn.nl>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
> 
> Hi,
> 
> sorry for the delay.
> Peter, I amended the patch to add a comment in the declaration of .name.
> If this is not what you had in mind (or if it is not sufficient), please tell
> me. I still kept your tested and S-o-b lines, but feel free to retract yourself :)
> 
> Cheers,
> Benjamin

Maybe it would be better to explain that the pointer is never NULL
because the memory is owned by the upper device (struct hid_device?),
then it is obvious that the memory is not allocated by this driver
itself.

With or without this elaboration the patch and comment is still correct,
so there is no reason to retract the R-b and T-b though.

Kind regards,
Peter

>  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 c8af315..e77658c 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;		/* will never be NULL and should not be freed */
>  	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) {
> +		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;
> 

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