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AIX Version 4.3 Kernel and Subsystems Technical Reference, Volume 1

rmmap_create Kernel Service


Defines an Effective Address [EA] to Real Address [RA] translation region.


#include <sys/ioacc.h>
#include <sys/adspace.h>
int rmmap_create (eaddrp, iomp, flags)
void **eaddrp;
struct io_map *iomp;
int flags;


eaddr Desired process effective address of the mapping region.
iomp The bus memory to which the effective address described by the eaddr parameter should correspond. For real memory, the bus id should be set to REALMEM_BID and the bus address should be set to the real memory address. The size field must be at least PAGESIZE, no larger than SEGSIZE, and a multiple of PAGESIZE. The key should be set to IO_MEM_MAP. The flags field is not used.
flags The flags select page and segment attributes of the translation. Not all page attribute flags are compatible. See below for the valid combinations of page attribute flags.
RMMAP_PAGE_W PowerPC "Write Through" page attribute. Write-through mode is not supported, and if this flag is set, EINVAL is reported.
RMMAP_PAGE_I PowerPC "Cache Inhibited" page attribute. This flag is valid for I/O mappings, but is not allowed for real memory mappings.
RMMAP_PAGE_M PowerPC "Memory Coherency Required" page attribute. This flag is optional for I/O mappings; however, it is required for memory mappings. The default operating mode of AIX for real memory pages has this bit set.
RMMAP_PAGE_G PowerPC "Guarded" page attribute. This flag is optional for I/O mappings, and must be 0 for real memory mappings. Note that although optional for I/O, it is strongly recommended that this be set for I/O mappings. When set, the processor will not make unnecessary (speculative) references to the page. This includes out of order read/write operations and branch fetching. When clear, normal PowerPC speculative execution rules apply. This bit does not exist on the 601 microprocessor and is ignored.
RMMAP_RDONLY When set, the page protection bits used in the HTAB will not allow write operations regardless of the setting of the key bit in the associated segment register. Exactly one of RMMAP_RDONLY and RMMAP_RDWR must be specified.
RMMAP_RDWR When set, the page protection bits used in the HTAB will allow read and write operations regardless of the setting of the key bit in the associated segment register. Exactly one of: RMMAP_RDONLY, and RMMAP_RDWR must be specified.
RMMAP_PRELOAD When set, the protection attributes of this region will be entered immediately into the hardware page table. This is very slow initially, but prevents each referenced page in the region from faulting in separately. This is only advisory. The rmmap_create64 reserves the right to preload regions which do not specify this flag and to ignore the flag on regions which do. This flag is not maintained as an attribute of the map region, it is used only during the current call.
RMMAP_INHERIT When set, this specifies that the translation region created by this rmmap_create invocation should be inherited on a fork operation, to the child process. This inheritance is achieved with copy-semantics. That is to say that the child will have its own private mapping to the same I/O or real memory address range as the parent.


The translation regions created with rmmap_create kernel service are maintained in I/O mapping segments. Any single such segment may translate up to 256 Megabytes of real memory or memory mapped I/O in a single region. The only granularity for which the rmmap_remove service may be invoked is a single mapping created by a single call to the rmmap_create.

There are constraints on the size of the mapping and the flags parameter, described later, which will cause the call to fail regardless of whether adequate effective address space exists.

If rmmap_create kernel service is called with the effective address of zero (0), the function attempts to find free space in the process address space. If successful, an I/O mapping segment is created and the effective address (which is passed by reference) is changed to the effective address which is mapped to the first page of the iomp memory.

If rmmap_create kernel service is called with a non-zero effective address, it is taken as the desired effective address which should translate to the passed iomp memory. This function verifies that the requested range is free. If not, it fails and returns EINVAL. If the mapping at the effective address is not contained in a single segment, the function fails and returns ENOSPC. Otherwise, the region is allocated and the effective address is not modified. The effective address is mapped to the first page of the iomp memory. References outside of the mapped regions but within the same segment are invalid.

The effective address (if provided) and the bus address must be a multiple of PAGESIZE or EINVAL is returned.

If rmmap_create kernel service is called with a length which is either not a multiple of PAGESIZE, is less than PAGESIZE, or is greater than SEGSIZE, EINVAL is returned. This return code takes precedence in cases where otherwise the segment would overflow and ENOSPC is returned.

I/O mapping segments are not inherited by child processes after a fork subroutine, except when RMMAP_INHERIT is specified. These segments are deleted by exec, exit, or rmmap_remove of the last range in a segment.

Only certain combinations of flags are permitted, depending on the type of memory being mapped. For real memory mappings, RMMAP_PAGE_M is required while RMMAP_PAGE_W, RMMAP_PAGE_I, and RMMAP_PAGE_G are not allowed. For I/O mappings, it is valid to specify only RMMAP_PAGE_M, with no other page attribute flags. It is also valid to specify RMMAP_PAGE_I and optionally, either or both of RMMAP_PAGE_M, and RMMAP_PAGE_G. RMMAP_PAGE_W is never allowed.

Execution Environment

The rmmap_create kernel service can only be called from the process environment.

Return Values

On successful completion, rmmap_create kernel service returns zero and modifies the effective address to the value at which the newly created mapping region was attached to the process address space. Otherwise, it returns one of:

EINVAL Some type of parameter error occurred. These include, but are not limited to, size errors and mutually exclusive flag selections.
ENOMEM The operating system could not allocate the necessary data structures to represent the mapping.
ENOSPC Effective address space exhausted in the region indicated by eaddr.
EPERM This hardware platform does not implement this service.

Implementation Specifics

The rmmap.create kernel service is part of the Base Operating System (BOS) Runtime.

This service only functions on PowerPC microprocessors.

The real address range described by the iomp parameter must be unique within this I/O mapping segment.

Related Information

The rmmap_remove kernel service.

Memory Kernel Services and Understanding Virtual Memory Manager Interfaces in AIX Version 4 Kernel Extensions and Device Support Programming Concepts.

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