Mac Developer Library

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IOBufferMemoryDescriptor Class Reference

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IOBufferMemoryDescriptor

Inheritance


  • IOBufferMemoryDescriptor

Conforms To


Not Applicable

Import Statement


Not Applicable

Objective-C

@import Kernel;

Availability


Available in OS X v10.0 and later.

Provides a simple memory descriptor that allocates its own buffer memory.

  • Creates a memory buffer with memory descriptor for that buffer.

    Declaration

    C++

    static IOBufferMemoryDescriptor * inTaskWithOptions( task_t inTask, IOOptionBits options, vm_size_t capacity, vm_offset_t alignment = 1);

    Parameters

    inTask

    The task the buffer will be allocated in.

    options

    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.

    capacity

    The number of bytes to allocate.

    alignment

    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.

    Return Value

    Returns an instance of class IOBufferMemoryDescriptor to be released by the caller, which will free the memory desriptor and associated buffer.

    Discussion

    Added in Mac 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.

  • Creates a memory buffer with memory descriptor for that buffer.

    Declaration

    C++

    static IOBufferMemoryDescriptor * inTaskWithPhysicalMask( task_tinTask, IOOptionBitsoptions, mach_vm_size_tcapacity, mach_vm_address_tmask);

    Parameters

    inTask

    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

    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.

    capacity

    The number of bytes to allocate.

    mask

    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.

    Return Value

    Returns an instance of class IOBufferMemoryDescriptor to be released by the caller, which will free the memory desriptor and associated buffer.

    Discussion

    Added in Mac 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.

Data Types

  • Declaration

    C++

    struct ExpansionData { IOMemoryMap *map; };

    Discussion

    This structure will be used to expand the capablilties of this class in the future.

Instance Variables

  • Reserved for future use. (Internal use only)

    Declaration

    C++

    ExpansionData * reserved;