IODataQueueShared.h

Includes:

Overview

Use the links in the table of contents to the left to access the documentation.

Typedefs

IODataQueueAppendix: A struct mapping to the appendix region of a data queue.
IODataQueueEntry: Represents an entry within the data queue
IODataQueueMemory: A struct mapping to the header region of a data queue.

IODataQueueAppendix

A struct mapping to the appendix region of a data queue.

typedef struct _IODataQueueAppendix { 
    UInt32 version; 
    mach_msg_header_t msgh; 
} IODataQueueAppendix;

Fields

version: The version of the queue appendix.
port: The notification port associated with this queue.

Discussion

This struct is variable sized dependent on the version. The struct represents the data queue appendix information.

IODataQueueEntry

Represents an entry within the data queue

typedef struct _IODataQueueEntry{ 
    UInt32 size; 
    UInt8 data[4]; 
} IODataQueueEntry;

Fields

size: The size of the following data region.
data: Represents the beginning of the data region. The address of the data field is a pointer to the start of the data region.

Discussion

This is a variable sized struct. The data field simply represents the start of the data region. The size of the data region is stored in the size field. The whole size of the specific entry is the size of a UInt32 plus the size of the data region.

IODataQueueMemory

A struct mapping to the header region of a data queue.

typedef struct _IODataQueueMemory { 
    UInt32 queueSize; 
    volatile UInt32 head; 
    volatile UInt32 tail; 
    IODataQueueEntry queue[1]; 
} IODataQueueMemory;

Fields

queueSize: The size of the queue region pointed to by the queue field.
head: The location of the queue head. This field is represented as a byte offset from the beginning of the queue memory region.
tail: The location of the queue tail. This field is represented as a byte offset from the beginning of the queue memory region.
queue: Represents the beginning of the queue memory region. The size of the region pointed to by queue is stored in the queueSize field.

Discussion

This struct is variable sized. The struct represents the data queue header information plus a pointer to the actual data queue itself. The size of the struct is the combined size of the header fields (3 * sizeof(UInt32)) plus the actual size of the queue region. This size is stored in the queueSize field.

Macro Definitions

DATA_QUEUE_ENTRY_HEADER_SIZE
DATA_QUEUE_MEMORY_APPENDIX_SIZE
DATA_QUEUE_MEMORY_HEADER_SIZE

DATA_QUEUE_ENTRY_HEADER_SIZE

#define DATA_QUEUE_ENTRY_HEADER_SIZE

Discussion

Represents the size of the data queue entry header independent of the actual size of the data in the entry. This is the overhead of each entry in the queue. The total size of an entry is equal to this value plus the size stored in the entry's size field (in IODataQueueEntry).

DATA_QUEUE_MEMORY_APPENDIX_SIZE

#define DATA_QUEUE_MEMORY_APPENDIX_SIZE

Discussion

Represents the size of the data queue memory appendix independent of the actual size of the queue data itself. The total size of the queue memory is equal to this value plus the size of queue header and size of the queue data region which is stored in the queueSize field of IODataQueueMeory.

DATA_QUEUE_MEMORY_HEADER_SIZE

#define DATA_QUEUE_MEMORY_HEADER_SIZE

Discussion

Represents the size of the data queue memory header independent of the actual size of the queue data itself. The total size of the queue memory is equal to this value plus the size of the queue appendix and the size of the queue data region which is stored in the queueSize field of IODataQueueMeory.

Last Updated: 2009-10-14