Contents

withSubRange

Create an IOMemoryDescriptor to describe a subrange of an existing descriptor.

Declaration

static IOSubMemoryDescriptor * withSubRange(
 IOMemoryDescriptor *of, 
 IOByteCountoffset, 
 IOByteCountlength, 
 IOOptionBitsoptions);

Parameters

  • of:

    The parent IOMemoryDescriptor of which a subrange is to be used for the new descriptor, which will be retained by the subrange IOMemoryDescriptor.

  • offset:

    A byte offset into the parent memory descriptor's memory.

  • length:

    The length of the subrange.

  • options:

    kIOMemoryDirectionMask (options:direction) This nibble indicates the I/O direction to be associated with the descriptor, which may affect the operation of the prepare and complete methods on some architectures.

Return Value

The created IOMemoryDescriptor on success, to be released by the caller, or zero on failure.

Overview

This method creates and initializes an IOMemoryDescriptor for memory consisting of a subrange of the specified memory descriptor. The parent memory descriptor is retained by the new descriptor.