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IOPreparationTable Options

This options field of the IOPreparationTable structure contains flags that have the following meanings:

• kIOMultipleRanges specifies that the rangeInfo field is to be interpreted as MultipleAddressRange, enabling a scatter-gather memory specification.
• kIOLogicalRanges specifies that the base fields of the AddressRange structures are logical addresses. If this option is omitted, the addresses are treated as physical addresses. Current versions of the Mac OS do not support specifying physical buffers, so the driver must always specify this option.
• kIOMinimalLogicalMapping specifies that the LogicalMappingTable structure is to be filled in with just the first and last mappings of each range, arranged in pairs. Minimal logical mappings are discussed in DMA Alignment Requirements.
• kIOShareMappingTables specifies that the system can use the driver's mapping tables instead of maintaining its own copies of the tables. Sharing mapping tables is discussed in Reducing Memory Usage.
• kIOIsInput specifies that data will be moved into main memory.
• kIOIsOutput specifies that data will be moved out of main memory.
• kIOCoherentDataPath indicates that the data path that will be used to access memory during the I/O operation is fully coherent with the main processor's data caches, making data cache manipulations unnecessary. Memory coherency with the instruction cache is not implied, however, so the appropriate instruction cache manipulations are performed regardless. This option is useful when the overall hardware architecture is not coherent, but the driver knows that the transfer will occur on a particular hardware path that is coherent. ( PrepareMemoryForIO operates according to the overall architecture and has no implicit way of knowing about individual data paths.) When in doubt, omit this option. Incorrectly omitting it merely slows operation, whereas incorrectly specifying this option can result in erroneous behavior and crashes.
• kIOClientIsUserMode indicates that PrepareMemoryForIO is being called on behalf of a nonprivileged client. If this option is specified, the memory ranges are checked for user-mode accessibility. If this option is omitted, the memory ranges are checked for privileged-level accessibility. Drivers can obtain the client's execution mode through the device's family programming interface (FPI). This option is not implemented in current versions of Mac OS. For compatibility with future Mac OS releases, drivers should omit it from the options. The FPI will perform the buffer access level checks on behalf of the driver.