Hot Removal

The sequence of events for hot removal of a USB device is as follows:

1. The hub driver, hubd(7D), waits for a port connect status change.

2. The hubd driver detects a port disconnect.

3. The hubd driver sends a disconnect event to the child client driver. If the child client driver is the hubd driver or the usb_mid(7D) multi-interface driver, then the child client driver propagates the event to its children.

4. The client driver receives the disconnect event notification in kernel thread context. Kernel thread context enables the driver's disconnect handler to block.

5. The client driver moves to the DISCONNECTED state. Outstanding I/O transfers fail with the completion reason of device not responding. All new I/O transfers and attempts to open the device node also fail. The client driver is not required to close pipes. The driver is required to save the device and driver context that needs to be restored if the device is reconnected.

6. The hubd driver attempts to offline the OS device node and its children in bottom-up order.

The following events take place if the device node is not open when the hubd driver attempts to offline the device node:

1. The client driver's detach(9E) entry point is called.

2. The device node is destroyed.

3. The port becomes available for a new device.

4. The hotplug sequence of events starts over. The hubd driver waits for a port connect status change.

The following events take place if the device node is open when the hubd driver attempts to offline the device node:

1. The hubd driver puts the offline request in the periodic offline retry queue.

2. The port remains unavailable for a new device.

If the device node was open when the hubd driver attempted to offline the device node and the user later closes the device node, the hubd driver periodic offlining of that device node succeeds and the following events take place:

1. The client driver's detach(9E) entry point is called.

2. The device node is destroyed.

3. The port becomes available for a new device.

4. The hotplug sequence of events starts over. The hubd driver waits for a port connect status change.

If the user closes all applications that use the device, the port becomes available again. If the application does not terminate or does not close the device, the port remains unavailable.