Handling Stream Request Blocks

The operating system dispatches all I/O requests on the device to the class driver. The class driver in turn requests hardware-specific information from the minidriver by passing SRBs to the minidriver. The class driver specifies the operation it requests in the Command member of the stream request block.

Both the minidriver as a whole, and each stream within the minidriver, may receive I/O requests. The minidriver must provide a StrMiniReceiveDevicePacket routine to handle device-wide requests. Each stream must support two routines to handle I/O requests: one for data requests, and one for control requests. The class driver calls the data request callback, StrMiniReceiveStreamDataPacket, to handle all read and write requests on a stream. All other requests for a stream are passed to StrMiniReceiveStreamControlPacket.

If the class driver is handling synchronization for the minidriver, it queues stream requests, and dispatches them to the minidriver one at a time. The class driver maintains three separate queues -- one for device requests, and one each for stream data and control requests. The minidriver may signal that it is ready for a new request from one of these queues as follows:

When the class driver calls StrMiniReceiveXXXPacket, it hands off the stream request block to the minidriver. The minidriver's routine has sole access to the stream request block until it signals to the class driver it has completed the request.

When the minidriver finishes processing a request, it should signal the class driver it has completed the request as follows:

1. The minidriver should set the status of the request in the Status field of the stream request block.

2. The minidriver should signal it has completed the request, by calling StreamClassDeviceNotification or StreamClassStreamNotification. To complete a device request, the minidriver calls StreamClassDeviceNotification with a NotificationType parameter of DeviceRequestComplete. To complete a stream request, the minidriver calls StreamClassStreamNotification with a NotificationType parameter of StreamRequestComplete.

3. If the class driver is handling synchronization, and if the minidriver has not yet signaled the class driver that it is ready for another request on this queue, it should do so now.

The minidriver can combine 2 and 3 by calling StreamClassCompleteRequestAndMarkQueueReady.

The minidriver processes requests asynchronously, so the class driver may need to cancel or time out a request. For these purposes, the minidriver must provide a StrMiniCancelPacket and a StrMiniRequestTimeout routine. The class driver calls the respective minidriver routine when it cancels or times out a request.

The class driver cancels a request when the underlying I/O request is canceled by the operating system. The class driver times out requests that take too long to process -- it decrements a counter of how many seconds until it times out a request in the TimeoutCounter member of the stream request block. If the minidriver must defer processing on a request for a long period of time, it should set the TimeoutCounter member to zero -- the class driver then will not time out the request. Once the minidriver resumes processing of the request, it should reset TimeoutCounter to be equal to the TimeoutOriginal member of the stream request block. The minidriver can reset TimeoutOriginal to change the length of time before the request times out. See HW_STREAM_REQUEST_BLOCK for details.