Creates a memory buffer with memory descriptor for that buffer.
The task the buffer will be mapped in. Pass NULL to create memory unmapped in any task (eg. for use as a DMA buffer).
Options for the allocation:
kIODirectionOut, kIODirectionIn - set the direction of the I/O transfer.
kIOMemoryPhysicallyContiguous - pass to request memory be physically contiguous. This option is heavily discouraged. The request may fail if memory is fragmented, may cause large amounts of paging activity, and may take a very long time to execute.
kIOMemoryKernelUserShared - pass to request memory that will be mapped into both the kernel and client applications.
kIOMapInhibitCache - allocate memory with inhibited cache setting.
kIOMapWriteThruCache - allocate memory with writethru cache setting.
kIOMapCopybackCache - allocate memory with copyback cache setting.
kIOMapWriteCombineCache - allocate memory with writecombined cache setting.
The number of bytes to allocate.
The buffer will be allocated with pages such that physical addresses will only have bits set present in physicalMask. For example, pass 0x00000000FFFFFFFFULL for a buffer to be accessed by hardware that has 32 address bits.
Returns an instance of class IOBufferMemoryDescriptor to be released by the caller, which will free the memory desriptor and associated buffer.
Added in OS X 10.5, this method allocates a memory buffer with a given size and alignment in the task's address space specified, and returns a memory descriptor instance representing the memory. It is recommended that memory allocated for I/O or sharing via mapping be created via IOBufferMemoryDescriptor. Options passed with the request specify the kind of memory to be allocated - pageablity and sharing are specified with option bits. This function may block and so should not be called from interrupt level or while a simple lock is held.