IOMemoryMap

IOMemoryMap is a memory mapping object in Apple's IOKit framework. It represents a region of memory that has been mapped into a caller's address space, typically created to expose device memory to user space or to support driver-internal DMA operations. The map is derived from an IOMemoryDescriptor through IOKit’s mapping interfaces. It records the base virtual address and the length of the mapped region and provides access to the mapped memory for the client or kernel code. The object manages the lifetime of the mapping and ensures proper synchronization and cache handling across unmapping or dereferencing.

Usage of IOMemoryMap centers on gaining access to a device or system memory region associated with a driver. A driver may obtain an IOMemoryMap to read from or write to the mapped memory, or to supply memory to a user client. Mappings can be created with options that specify data transfer direction or caching semantics, among other settings. When the IOMemoryMap is released, the mapping is typically unmapped and any necessary cache or state flushes are performed.

Access and safety considerations are important: interacting with mapped memory requires respecting alignment, size, and boundary constraints, and operations involving user-space memory must observe appropriate permissions and synchronization rules. Proper use of IOMemoryMap helps ensure efficient data transfer between devices and software while maintaining system stability.

See also: IOKit, IOMemoryDescriptor, IOUserClient, DMA.