important type for driver

IOReturn: IOKit/IOReturn.h

IOByteCount: IOKit/IOTypes.h

SCSITaskIdentifier: IOKit/scsi/SCSITask.h

IOBufferMemoryDescriptor: IOKit/IOBufferMemoryDescriptor.h

SCSI_Sense_Data: IOKit/scsi/SCSICmds_REQUEST_SENSE_Defs.h

UInt64: libkern/OSTypes.h

NULL: string.h

IO flow

AsyncReadWrite  -->  IssueRead  or IssueWrite

combine c and c++ for apple driver

set build option:

gcc 4.0 language -->  compile source as -->  c++

info.plist for driver

IOMatchCategory:

set IODefaultMatchCategory to compare with other driver

the driver with higher probe score will win

IOIteratorNext

iterator must be released

the element got from IOIteratorNext must be released 

ex:

ele= IOIteratorNext(iter)

while(ele != IO_OBJECT_NULL){

   IOObjectRelease(ele);

   ele = IOIteratorNext(iter);

}

IOObjectRelease(iter);

ioclasscount

the instance count of the class

useful for tracking leaks