vmbus: add driver_override support

Add support for overriding the default driver for a VMBus device
in the same way that it can be done for PCI devices. This patch
adds the /sys/bus/vmbus/devices/.../driver_override file
and the logic for matching.

This is used by driverctl tool to do driver override.
https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.com%2Fdriverctl%2Fdriverctl&data=02%7C01%7Ckys%40microsoft.com%7C42e803feb2c544ef6ea908d5fd538878%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636693457619960040&sdata=kEyYHRIjNZCk%2B37moCSqbrZL426YccNQrsWpENcrZdw%3D&reserved=0

Signed-off-by: Stephen Hemminger <[e-mail]>
Signed-off-by: K. Y. Srinivasan <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/ABI/testing/sysfs-bus-vmbus

···
+What:		/sys/bus/vmbus/devices/.../driver_override
+Date:		August 2019
+Contact:	Stephen Hemminger <[e-mail]>
+Description:
+		This file allows the driver for a device to be specified which
+		will override standard static and dynamic ID matching.  When
+		specified, only a driver with a name matching the value written
+		to driver_override will have an opportunity to bind to the
+		device.  The override is specified by writing a string to the
+		driver_override file (echo uio_hv_generic > driver_override) and
+		may be cleared with an empty string (echo > driver_override).
+		This returns the device to standard matching rules binding.
+		Writing to driver_override does not automatically unbind the
+		device from its current driver or make any attempt to
+		automatically load the specified driver.  If no driver with a
+		matching name is currently loaded in the kernel, the device
+		will not bind to any driver.  This also allows devices to
+		opt-out of driver binding using a driver_override name such as
+		"none".  Only a single driver may be specified in the override,
+		there is no support for parsing delimiters.
+

drivers/hv/vmbus_drv.c

···
 }
 static DEVICE_ATTR_RO(device);
 
+static ssize_t driver_override_store(struct device *dev,
+				     struct device_attribute *attr,
+				     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);
+
+	kfree(old);
+
+	return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct hv_device *hv_dev = device_to_hv_device(dev);
+	ssize_t len;
+
+	device_lock(dev);
+	len = snprintf(buf, PAGE_SIZE, "%s\n", hv_dev->driver_override);
+	device_unlock(dev);
+
+	return len;
+}
+static DEVICE_ATTR_RW(driver_override);
+
 /* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
 static struct attribute *vmbus_dev_attrs[] = {
 	&dev_attr_id.attr,
···
 	&dev_attr_channel_vp_mapping.attr,
 	&dev_attr_vendor.attr,
 	&dev_attr_device.attr,
+	&dev_attr_driver_override.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(vmbus_dev);
···
 	return true;
 }
 
-/*
- * Return a matching hv_vmbus_device_id pointer.
- * If there is no match, return NULL.
- */
-static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv,
-					const uuid_le *guid)
+static const struct hv_vmbus_device_id *
+hv_vmbus_dev_match(const struct hv_vmbus_device_id *id, const uuid_le *guid)
+
+{
+	if (id == NULL)
+		return NULL; /* empty device table */
+
+	for (; !is_null_guid(&id->guid); id++)
+		if (!uuid_le_cmp(id->guid, *guid))
+			return id;
+
+	return NULL;
+}
+
+static const struct hv_vmbus_device_id *
+hv_vmbus_dynid_match(struct hv_driver *drv, const uuid_le *guid)
 {
 	const struct hv_vmbus_device_id *id = NULL;
 	struct vmbus_dynid *dynid;
 
-	/* Look at the dynamic ids first, before the static ones */
 	spin_lock(&drv->dynids.lock);
 	list_for_each_entry(dynid, &drv->dynids.list, node) {
 		if (!uuid_le_cmp(dynid->id.guid, *guid)) {
···
 	}
 	spin_unlock(&drv->dynids.lock);
 
-	if (id)
-		return id;
+	return id;
+}
 
-	id = drv->id_table;
-	if (id == NULL)
-		return NULL; /* empty device table */
+static const struct hv_vmbus_device_id vmbus_device_null = {
+	.guid = NULL_UUID_LE,
+};
 
-	for (; !is_null_guid(&id->guid); id++)
-		if (!uuid_le_cmp(id->guid, *guid))
-			return id;
+/*
+ * Return a matching hv_vmbus_device_id pointer.
+ * If there is no match, return NULL.
+ */
+static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv,
+							struct hv_device *dev)
+{
+	const uuid_le *guid = &dev->dev_type;
+	const struct hv_vmbus_device_id *id;
 
-	return NULL;
+	/* When driver_override is set, only bind to the matching driver */
+	if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+		return NULL;
+
+	/* Look at the dynamic ids first, before the static ones */
+	id = hv_vmbus_dynid_match(drv, guid);
+	if (!id)
+		id = hv_vmbus_dev_match(drv->id_table, guid);
+
+	/* driver_override will always match, send a dummy id */
+	if (!id && dev->driver_override)
+		id = &vmbus_device_null;
+
+	return id;
 }
 
 /* vmbus_add_dynid - add a new device ID to this driver and re-probe devices */
···
 	if (retval)
 		return retval;
 
-	if (hv_vmbus_get_id(drv, &guid))
+	if (hv_vmbus_dynid_match(drv, &guid))
 		return -EEXIST;
 
 	retval = vmbus_add_dynid(drv, &guid);
···
 	if (is_hvsock_channel(hv_dev->channel))
 		return drv->hvsock;
 
-	if (hv_vmbus_get_id(drv, &hv_dev->dev_type))
+	if (hv_vmbus_get_id(drv, hv_dev))
 		return 1;
 
 	return 0;
···
 	struct hv_device *dev = device_to_hv_device(child_device);
 	const struct hv_vmbus_device_id *dev_id;
 
-	dev_id = hv_vmbus_get_id(drv, &dev->dev_type);
+	dev_id = hv_vmbus_get_id(drv, dev);
 	if (drv->probe) {
 		ret = drv->probe(dev, dev_id);
 		if (ret != 0)

include/linux/hyperv.h

···
 	u16 device_id;
 
 	struct device device;
+	char *driver_override; /* Driver name to force a match */
 
 	struct vmbus_channel *channel;
 	struct kset	     *channels_kset;