Creates a memory buffer with memory descriptor for that buffer.
The task the buffer will be allocated in.
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.
kIOMemoryPageable - pass to request memory be non-wired - the default for kernel allocated memory is wired.
kIOMemoryPurgeable - pass to request memory that may later have its purgeable state set with IOMemoryDescriptor::setPurgeable. Only supported for kIOMemoryPageable allocations.
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 minimum required alignment of the buffer in bytes - 1 is the default for no required alignment. For example, pass 256 to get memory allocated at an address with bits 0-7 zero.
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 10.2, 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.