+Boolean IOSharedDataQueue::enqueue(void * data, UInt32 dataSize)
+{
+ const UInt32 head = dataQueue->head; // volatile
+ const UInt32 tail = dataQueue->tail;
+ const UInt32 entrySize = dataSize + DATA_QUEUE_ENTRY_HEADER_SIZE;
+ IODataQueueEntry * entry;
+
+ // Check for overflow of entrySize
+ if (dataSize > UINT32_MAX - DATA_QUEUE_ENTRY_HEADER_SIZE) {
+ return false;
+ }
+ // Check for underflow of (getQueueSize() - tail)
+ if (getQueueSize() < tail) {
+ return false;
+ }
+
+ if ( tail >= head )
+ {
+ // Is there enough room at the end for the entry?
+ if ((entrySize <= UINT32_MAX - tail) &&
+ ((tail + entrySize) <= getQueueSize()) )
+ {
+ entry = (IODataQueueEntry *)((UInt8 *)dataQueue->queue + tail);
+
+ entry->size = dataSize;
+ memcpy(&entry->data, data, dataSize);
+
+ // The tail can be out of bound when the size of the new entry
+ // exactly matches the available space at the end of the queue.
+ // The tail can range from 0 to dataQueue->queueSize inclusive.
+
+ OSAddAtomic(entrySize, (SInt32 *)&dataQueue->tail);
+ }
+ else if ( head > entrySize ) // Is there enough room at the beginning?
+ {
+ // Wrap around to the beginning, but do not allow the tail to catch
+ // up to the head.
+
+ dataQueue->queue->size = dataSize;
+
+ // We need to make sure that there is enough room to set the size before
+ // doing this. The user client checks for this and will look for the size
+ // at the beginning if there isn't room for it at the end.
+
+ if ( ( getQueueSize() - tail ) >= DATA_QUEUE_ENTRY_HEADER_SIZE )
+ {
+ ((IODataQueueEntry *)((UInt8 *)dataQueue->queue + tail))->size = dataSize;
+ }
+
+ memcpy(&dataQueue->queue->data, data, dataSize);
+ OSCompareAndSwap(dataQueue->tail, entrySize, &dataQueue->tail);
+ }
+ else
+ {
+ return false; // queue is full
+ }
+ }
+ else
+ {
+ // Do not allow the tail to catch up to the head when the queue is full.
+ // That's why the comparison uses a '>' rather than '>='.
+
+ if ( (head - tail) > entrySize )
+ {
+ entry = (IODataQueueEntry *)((UInt8 *)dataQueue->queue + tail);
+
+ entry->size = dataSize;
+ memcpy(&entry->data, data, dataSize);
+ OSAddAtomic(entrySize, (SInt32 *)&dataQueue->tail);
+ }
+ else
+ {
+ return false; // queue is full
+ }
+ }
+
+ // Send notification (via mach message) that data is available.
+
+ if ( ( head == tail ) /* queue was empty prior to enqueue() */
+ || ( dataQueue->head == tail ) ) /* queue was emptied during enqueue() */
+ {
+ sendDataAvailableNotification();
+ }
+
+ return true;
+}
+
projects / apple / xnu.git / commitdiff
