hv: Use driver_set_override() instead of open-coding

Use a helper to set driver_override to the reduce amount of duplicated
code.  Make the driver_override field const char, because it is not
modified by the core and it matches other subsystems.
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220419113435.246203-5-krzysztof.kozlowski@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/vmbus_drv.c

@@ -575,31 +575,11 @@ static ssize_t driver_override_store(struct device *dev,
 				     const char *buf, size_t count)
 {
 	struct hv_device *hv_dev = device_to_hv_device(dev);
-	char *driver_override, *old, *cp;
-
-	/* We need to keep extra room for a newline */
-	if (count >= (PAGE_SIZE - 1))
-		return -EINVAL;
-
-	driver_override = kstrndup(buf, count, GFP_KERNEL);
-	if (!driver_override)
-		return -ENOMEM;
-
-	cp = strchr(driver_override, '\n');
-	if (cp)
-		*cp = '\0';
-
-	device_lock(dev);
-	old = hv_dev->driver_override;
-	if (strlen(driver_override)) {
-		hv_dev->driver_override = driver_override;
-	} else {
-		kfree(driver_override);
-		hv_dev->driver_override = NULL;
-	}
-	device_unlock(dev);
+	int ret;
 
-	kfree(old);
+	ret = driver_set_override(dev, &hv_dev->driver_override, buf, count);
+	if (ret)
+		return ret;
 
 	return count;
 }

include/linux/hyperv.h

@@ -1257,7 +1257,11 @@ struct hv_device {
 	u16 device_id;
 
 	struct device device;
-	char *driver_override; /* Driver name to force a match */
+	/*
+	 * Driver name to force a match.  Do not set directly, because core
+	 * frees it.  Use driver_set_override() to set or clear it.
+	 */
+	const char *driver_override;
 
 	struct vmbus_channel *channel;
 	struct kset	     *channels_kset;