test

Writing Device Drivers

Hot Reinsertion

The following events take place if a previously-removed device is reinserted into the same port while the device node of the device is still open:

  1. The hub driver, hubd(7D), detects a port connect.

  2. The hubd driver restores the bus address and the device configuration.

  3. The hubd driver cancels the offline retry request.

  4. The hubd driver sends a connect event to the client driver.

  5. The client driver receives the connect event.

  6. The client driver determines whether the new device is the same as the device that was previously connected. The client driver makes this determination first by comparing device descriptors. The client driver might also compare serial numbers and configuration descriptor clouds.

The following events might take place if the client driver determines that the current device is not the same as the device that was previously connected:

  1. The client driver might issue a warning message to the console.

  2. The user might remove the device again. If the user removes the device again, the hot remove sequence of events starts over. The hubd driver detects a port disconnect. If the user does not remove the device again, the following events take place:

    1. The client driver remains in the DISCONNECTED state, failing all requests and opens.

    2. The port remains unavailable. The user must close and disconnect the device to free the port.

    3. The hotplug sequence of events starts over when the port is freed. The hubd driver waits for a port connect status change.

The following events might take place if the client driver determines that the current device is the same as the device that was previously connected:

  1. The client driver might restore its state and continue normal operation. This policy is up to the client driver. Audio speakers are a good example where the client driver should continue.

  2. If it is safe to continue using the reconnected device, the hotplug sequence of events starts over. The hubd driver waits for a port connect status change. The device is in service once again.