[PATCH 1/3] driver core: bus: introduce can_remove()

[Hamza Mahfooz <hamza.mahfooz@amd.com>]

Currently, drivers have no mechanism to block requests to unbind
devices. However, this can cause resource leaks and leave the device in
an inconsistent state, such that rebinding the device may cause a hang
or otherwise prevent the device from being rebound. So, introduce
the can_remove() callback to allow drivers to indicate if it isn't
appropriate to remove a device at the given time.

Cc: stable@vger.kernel.org
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
---
 drivers/base/bus.c         | 4 ++++
 include/linux/device/bus.h | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index daee55c9b2d9..7c259b01ea99 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -239,6 +239,10 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf,
 
 	dev = bus_find_device_by_name(bus, NULL, buf);
 	if (dev && dev->driver == drv) {
+		if (dev->bus && dev->bus->can_remove &&
+		    !dev->bus->can_remove(dev))
+			return -EBUSY;
+
 		device_driver_detach(dev);
 		err = count;
 	}
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index 5ef4ec1c36c3..c9d4af0ed3b8 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -46,6 +46,7 @@ struct fwnode_handle;
  *		be called at late_initcall_sync level. If the device has
  *		consumers that are never bound to a driver, this function
  *		will never get called until they do.
+ * @can_remove: Called before attempting to remove a device from this bus.
  * @remove:	Called when a device removed from this bus.
  * @shutdown:	Called at shut-down time to quiesce the device.
  *
@@ -85,6 +86,7 @@ struct bus_type {
 	int (*uevent)(const struct device *dev, struct kobj_uevent_env *env);
 	int (*probe)(struct device *dev);
 	void (*sync_state)(struct device *dev);
+	bool (*can_remove)(struct device *dev);
 	void (*remove)(struct device *dev);
 	void (*shutdown)(struct device *dev);
 
-- 
2.43.0