Document revision date: 30 March 2001

On Alpha systems, allows a process to create a memory-resident global demand-zero section and to map a section of its address space to the global section. Shared page table sections can also be created.

This service accepts 64-bit addresses.

Format

SYS$CRMPSC_GDZRO_64 gs_name_64 ,ident_64 ,prot ,length_64 ,region_id_64 ,section_offset_64 ,acmode ,flags ,return_va_64 ,return_length_64 [[[[,start_va_64] ,map_length_64] ,reserved_length_64] ,rad_mask]

C Prototype

int sys$crmpsc_gdzro_64 (void *gs_nam_64, struct _secid *ident_64, unsigned int prot, unsigned __int64 length_64, struct _generic_64 *region_id_64, unsigned __int64 section_offset_64, unsigned int acmode, unsigned int flags, void *(*(return_va_64)), unsigned __int64 *return_length_64,...);

Arguments

gs_name_64

OpenVMS usage:	section_name
type:	character-coded text string
access:	read only
mechanism:	by 32- or 64-bit descriptor--fixed-length string descriptor

Name of the global section. The gs_name_64 argument is the 32- or 64-bit virtual address of a naturally aligned 32- or 64-bit string descriptor pointing to this name string.

ident_64

OpenVMS usage:	section_id
type:	quadword (unsigned)
access:	read only
mechanism:	by 32- or 64-bit reference

Identification value specifying the version number of a global section. The ident_64 argument is a quadword containing three fields. The ident_64 argument is the 32- or 64-bit virtual address of a naturally aligned quadword that contains the identification value.

The first longword specifies the matching criteria in its low-order 2 bits. The valid values, symbolic names by which they can be specified, and their meanings are as follows:

Value	Symbolic Name	Match Criteria
0	SEC$K_MATALL	Match all versions of the section.
1	SEC$K_MATEQU	Match only if major and minor identifications match.
2	SEC$K_MATLEQ	Match if the major identifications are equal and the minor identification of the mapper is less than or equal to the minor identification of the global section.

When a section is mapped at creation time, the match control field is ignored. If you specify the ident_64 argument as 0, the version number and match control fields default to 0.

The version number is in the second longword. The version number contains two fields: a minor identification in the low-order 24 bits and a major identification in the high-order 8 bits. You can assign values for these fields by installation convention to differentiate versions of global sections. If no version number is specified when a section is created, processes that specify a version number when mapping cannot access the global section.

prot

OpenVMS usage:	file_protection
type:	longword (unsigned)
access:	read only
mechanism:	by value

Protection to be applied to the global demand-zero section. The mask contains four 4-bit fields. Bits are read from right to left in each field. The following diagram depicts the mask:

Cleared bits indicate that read, write, execute, and delete access, in that order, are granted to the particular category of user. Only read, write, and execute access are meaningful for section protection. Delete access bits are ignored. Read access also grants execute access for those situations where execute access applies. If zero is specified, read access and write access are granted to all users.

length_64

region_id_64

The file VADEF.H in SYS$STARLET_C.TLB and the $VADEF macro in STARLET.MLB define a symbolic name for each of the three default regions in P0, P1, and P2 space.

The following region IDs are defined:

Symbol	Region
VA$C_P0	Program region
VA$C_P1	Control region
VA$C_P2	64-bit program region

Other region IDs, as returned by the $CREATE_REGION_64 service, can be specified.

section_offset_64

If a shared page table region is specified by the region_id_64 argument, section_offset_64 must be an even multiple of the number of bytes that can be mapped by a CPU-specific page table page.

acmode

If the memory-resident global section is created with shared page tables, this is the access mode that is stored in the owner, read, and write fields of the corresponding shared page table entries (PTEs).

The $PSLDEF macro in STARLET.MLB and the file PSLDEF.H in SYS$STARLET_C.TLB define the following symbols and their values for the four access modes:

Value	Symbolic Name	Access Mode
0	PSL$C_KERNEL	Kernel
1	PSL$C_EXEC	Executive
2	PSL$C_SUPER	Supervisor
3	PSL$C_USER	User

The most privileged access mode used is the access mode of the caller. The calling process can delete pages only if those pages are owned by an access mode equal to or less privileged than the access mode of the calling process.

Address space cannot be created within a region that has a create mode associated with it that is more privileged than the caller's mode. The condition value SS$_IVACMODE is returned if the caller is less privileged than the create mode for the region.

flags

The following table describes each flag that is valid for the $CRMPSC_GDZRO_64 service:

Flag	Description
SEC$M_DZRO	Pages are demand-zero pages. By default, this flag is always present in this service and cannot be disabled.
SEC$M_EXPREG	Pages are mapped into the first available space at the current end of the specified region. If the /ALLOCATE qualifier was specified when the global section was registered in the Reserved Memory Registry, virtually aligned addresses after the first available space are chosen for the mapping.
SEC$M_GBL	Pages form a global section. By default, this flag is always present in this service and cannot be disabled.
SEC$M_NO_OVERMAP	Pages cannot overmap existing address space.
SEC$M_PERM	Global section is permanent.
SEC$M_RAD_HINT	When set, the argument rad_mask is used as a mask of RADs from which to allocate memory. See the rad_mask argument description for more information.
SEC$M_READ_ONLY_SHPT	Create shared table pages for the section that allow read access only.
SEC$M_SHMGS	Create a shared-memory global section.
SEC$M_SYSGBL	Pages form a system global section. By default, pages form a group global section.
SEC$M_MRES	Pages form a memory-resident section. By default, this page is always present in this service and cannot be disabled.
SEC$M_WRT	Pages form a read/write section. By default, this flag is always present in this service and cannot be disabled.

All other bits in the flags argument are reserved for future use by Compaq and should be specified as 0. The condition value SS$_IVSECFLG is returned if any undefined bits are set or if an invalid combination of flags is set.

return_va_64

If a shared page table region is specified by the region_id_64 argument and the SEC$M_EXPREG flag is set, the returned virtual address is aligned to a CPU-specific page table page boundary.

return_length_64

start_va_64

If SEC$M_EXPREG is clear, start_va_64 is nonzero, and a shared page table region is specified, the specified starting address must be aligned to a natural page table page boundary; otherwise, the condition value SS$_VA_NOTPAGALGN is returned.

If the /ALLOCATE qualifier was specified when the memory-resident global section was registered in the Reserved Memory Registry and start_va_64 is aligned to a multiple of CPU-specific pages appropriate for taking advantage of granularity hints (8, 64, or 512 pages), then granularity hints are used to map to the global section.

map_length_64

If a shared page table region is specified by the region_id_64 argument, map_length_64 must be an even multiple of the number of bytes that can be mapped by a CPU-specific page table page or must include the last page within the global section.

reserved_length_64

If reserved_length_64 is not specified or is specified as 0, no reserved length is returned to the caller.

If the memory-resident global section is not registered, reserved_length_64 is written with the value 0.

rad_mask

The rad_mask argument is considered only if the SEC$M_RAD_HINT flag is specified. Otherwise, this argument is ignored.

On a system that does not support resource affinity domains (RADs), specifying 1 for the rad_mask argument is allowed.

Note: OpenVMS support for RADs is available only on the new AlphaServer GS series systems. For more information about using RADs, refer to the OpenVMS Alpha Partitioning and Galaxy Guide.

Description

The Create and Map to Global Demand-Zero Section service allows a process to create and map to a memory-resident global demand-zero section. If you set the SEC$M_SHMGS flag, the section is created as a Galaxy-wide global demand-zero section in shared memory.

You must call either the $CREATE_GDZRO service or the $CRMPSC_GDZRO_64 service on each instance where the Galaxy shared memory will be accessed.

Memory-resident or Galaxy-wide global sections contain demand-zero allocation pages that are writable and memory resident. All pages in these types of global section are shared by all processes that map to the global section.

If the $CRMPSC_GDZRO_64 service specifies a global section that already exists, the service maps to it only if it is a memory-resident global section. All pages in the memory-resident global section are shared by all processes that map to the global section.

The global demand-zero pages are always resident in memory and are not backed up by any file on any disk. The global pages are not charged against any page file quota. The process must have the rights identifier VMS$MEM_RESIDENT_USER to create a memory-resident global section; otherwise, the error status SS$_NOMEMRESID is returned.

The pages are always resident in memory and are not backed up by any file on any disk. The pages are not placed into the process's working set list when the process maps to the global section and the virtual memory is referenced by the process. The pages are also not charged against the process's working set quota or against any page-file quota.

Only memory-resident sections can be registered with the Reserved Memory Registry in the SYSMAN facility. Memory for Galaxy-wide shared sections is reserved through appropriate settings of the console environment parameters.

If the memory-resident global section is either not registered in the Reserved Memory Registry or if the /NOALLOCATE qualifier was specified when the global section was registered in the Reserved Memory Registry, invalid global PTEs are written to the global page table and invalid PTEs are placed in the process page table. Physical memory is not allocated until the virtual memory is referenced.

If the global section is registered in the Reserved Memory Registry, the size of the global section need not match the reserved size. If the global section is not registered in the Reserved Memory Registry or if the reserved size is smaller than the size of the global section, the error status SS$_INSFLPGS is returned if there are not enough fluid pages in the system to satisfy the request.

If the /ALLOCATE qualifier was specified when the global section was registered in the Reserved Memory Registry, contiguous, aligned physical pages are preallocated during system initialization for this global section. Valid page table entries are placed in the global page table and in the process page table. If the reserved preallocated memory is smaller than the size of the global section, the error SS$_MRES_PFNSMALL is returned and the global section is not created.

If the memory-resident global section is not registered in the Reserved Memory Registry or if the /PAGE_TABLES qualifier was specified when the global section was registered in the Reserved Memory Registry, shared page tables are created for the global section.

For more information about using the SYSMAN utility to create entries to the Reserved Memory Registry, refer to the OpenVMS System Management Utilities Reference Manual.

Shared page tables consume the same internal OpenVMS data structures as a global section. The system parameters GBLPAGES and GBLSECTIONS must account for the additional global pages and the additional global section.

To use the shared page tables associated with a memory-resident global section, you must first create a shared page-table region (with $CREATE_REGION_64). To map to the memory-resident global section using the shared page tables, you must do the following:

• Specify a shared page-table region in the region_id_64 argument.
• Set the flag SEC$M_EXPREG or provide a CPU-specific page table page aligned virtual address in the start_va_64 argument.
• Specify a value for the section_offset_64 argument that is an even multiple of bytes mapped by a CPU-specific page table page or zero.
• Specify a value for the map_length_64 argument that is an even multiple of bytes mapped by a CPU-specific page table page or zero, or include the last page of the section.

See the description of the $CREATE_REGION_64 service for information about calculating virtual addresses that are aligned to a CPU-specific page table page boundary.

The memory-resident global section can be mapped with shared page tables or private page tables. The following table lists the factors associated with determining whether the mapping occurs with shared page tables or with private page tables:

Global Section Created with Shared Page Tables	Shared Page Table Region Specified by region_id_64	Type of Page Tables Used in Mapping
No	No	Private
No	Yes	Private
Yes	No	Private
Yes	Yes	Shared

In general, if the flag SEC$M_EXPREG is set, the first free virtual address within the specified region is used to map to the global section.

If the flag SEC$M_EXPREG is set and the region_id_64 argument indicates a shared page table region, the first free virtual address within the specified region is rounded up to a CPU-specific page table page boundary and used to map to the global section.

If the flag SEC$M_EXPREG is set and if the /ALLOCATE qualifier was specified with the SYSMAN command RESERVED_MEMORY ADD for the memory-resident global section, the first free virtual address within the specified region is rounded up to the same virtual alignment as the physical alignment of the preallocated pages and used to map to the global section. Granularity hints are set appropriately for each process private PTE.

In general, if the flag SEC$M_EXPREG is clear, the virtual address in the start_va_64 argument is used to map to the global section.

If the flag SEC$M_EXPREG is clear, the value specified in the start_va_64 argument can determine if the mapping is possible and if granularity hints are used in the private page tables. If a shared page table region is specified by the region_id_64 argument, the virtual address specified by the start_va_64 argument must be on an even CPU-specific page table page boundary or an error is returned by this service. If the region_id_64 argument does not specify a shared page table region and /ALLOCATE was specified with the SYSMAN command RESERVED_MEMORY ADD for this global section, granularity hints are used only if the virtual alignment of start_va_64 is appropriate for the use of granularity hints (either 8-page, 64-page, or 512-page alignment).

Whenever granularity hints are being used within the mapping of a memory-resident global section, if the length_64 argument is not an exact multiple of the alignment factor, lower granularity hints factors are used as appropriate at the higher addressed portion of the global section. If the section_offset_64 argument is specified, a lower granularity hint factor can be used throughout the mapping of the global section to match the physical alignment of the first page mapped.

When you map a Galaxy shared section or a memory resident section that has an associated shared page table section, you have the following options for accessing data:

Table SYS-7 Shared Page Tables

Shared Page Tables	Read Only	Read and Write
None created	Do not set the SEC$M_WRT flag in the map request. Private page tables will always be used, even if you are specifying a shared page table region into which to map the section.	Set the SEC$M_WRT flag in the map request. Private page tables will always be used, even if you are specifying a shared page table region into which to map the section.
Write access	Do not set the SEC$M_WRT flag in the map request. Ensure that private page tables will be used. Do not specify a shared page table region into which to map the section. If you do, the error status SS$_IVSECFLG is returned.	Set the SEC$M_WRT flag in the map request. The shared page table section will be used for mapping if you specify a shared page table region into which to map the section.
Read access	Do not set the SEC$M_WRT flag in the map request. The shared page table section will be used for mapping if you specify a shared page table region into which to map the section.	Set the SEC$M_WRT flag in the map request. Ensure that private page tables will be used. Do not specify a shared page table region into which to map the section. If you do, the error status SS$_IVSECFLG is returned.

Notes Shared page tables for Galaxy shared sections are also implemented as Galaxy shared sections. This implies that they allow either read access only on all OpenVMS instances connected to this section or read and write access on all instances. The setting of the SEC$M_READ_ONLY_SHPT flag as requested by the first instance to create the section is used on all instances. Previous Next Contents Index   privacy and legal statement   4527PRO_023.HTML