On Dec 17 2014 or thereabouts, Peter Wu wrote:

On Tuesday 16 December 2014 17:06:02 Benjamin Tissoires wrote:

quoted

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 <redacted>
---
 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 <redacted>
Tested-by: Peter Wu <redacted>

Thanks! (and thanks for the other v3)

Cheers,
Benjamin

Kind regards,
Peter

quoted

+		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;