Updated: 11 December 1998

OpenVMS System Services Reference Manual

On Alpha systems, creates a permanent, memory-resident, global demand-zero section to which processes can map. Shared page table sections can also be created.

This service accepts 64-bit addresses.

Format

SYS$CREATE_GDZRO gs_name_64 ,ident_64 ,prot ,length_64 ,acmode ,flags [,reserved_length_64]

C Prototype

int sys$create_gdzro (void *gs_name_64, struct _secid *ident_64, unsigned int prot, unsigned __int64 length_64, unsigned int acmode, unsigned int flags,...);

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 the 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. 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.

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 0 is specified, read access and write access are granted to all users.

length_64

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

flags

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.

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.

Description

The Create Permanent Global Demand Zero Section service allows a process to create a permanent, memory-resident, global demand-zero section. Global demand-zero sections contain demand-zero allocation pages that are writable and memory resident. All pages in the memory-resident global demand-zero 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. To call this system service, the process must have the rights identifier VMS$MEM_RESIDENT_USER. The error status SS$_NOMEMRESID is returned if the caller has not been granted this identifier.

Memory-resident global 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 not charged against the process's working set quota.

If the global section is 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. When the global section is mapped, invalid page table entries are placed in the process page table. Physical memory is not allocated until the pages are 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 when the global section is mapped, valid page table entries are placed in the process page table. With the proper virtual alignment, granularity hints (GH) are used to map to the global pages.

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

If the /ALLOCATE and /PAGE_TABLE qualifiers were 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, and granularity hints are used to map to the shared page table sections.

The following table lists the factors affecting the creation of shared page tables for memory-resident global sections. The /ALLOCATE and the /PAGE_TABLES qualifiers pertain to the Reserved Memory Registry command RESERVED_MEMORY ADD entered for the memory-resident global section being created. For more information about using the SYSMAN utility to create entries to the Reserved Memory Registry, see the OpenVMS System Management Utilities Reference Manual.

/ALLOCATE	/PAGE_TABLES	Outcome
Not registered	Not registered	Shared page tables created. Shared page tables cannot use GH. Returns SS$_CREATED_SHPT.
No	No	No shared page tables created. Returns SS$_CREATED.
No	Yes	Shared page tables created. Shared page tables cannot use GH. Returns SS$CREATED_SHPT.
Yes	No	No shared page tables created. Returns SS$_CREATED.
Yes	Yes	Shared page tables created. Shared page tables can use GH. Returns SS$_CREATED_SHPT.

Shared page tables consume the same internal OpenVMS data structures as global sections. 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, a process must first create a shared page table region (with SYS$CREATE_REGION_64). Additionally, a subsequent request to map to the memory-resident global section must do the following:

• Specify a shared page table region to the mapping request.
• Specify the same access mode as specified by the acmode argument to this service.
• Set the flag SEC$M_WRT in the mapping request.
• Set the flag SEC$M_EXPREG in the mapping request or provide a CPU-specific page table page aligned virtual address. (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.)

If a shared page table region is not specified, process-private page tables are used to map to the global section.

If the service returns an error status value that is neither SS$_INSFLPGS nor SS$_MRES_PFNSMALL, a value is not returned in the reserved_length_64 argument.

If the service returns a successful condition value or if SS$_INSFLPGS or SS$_MRES_PFNSMALL is returned and the reserved_length_64 argument is specified as a nonzero address, the length in bytes of the global section as registered in the Reserved Memory Registry is returned in the reserved_length_64 argument.

Required Privileges

To create a permanent memory-resident global DZRO section, the process must have the following privileges or rights identifiers:

• SYSGBL privilege to create a system global section (if flag SEC$M_SYSGBL is set)
• PRMGBL privilege to create a permanent global section
• VMS$MEM_RESIDENT_USER rights identifier to create a memory-resident section

Required Quota

None

Related Services

$CRMPSC, $CRMPSC_GDZRO_64, $CRMPSC_GPFILE_64, $DGBLSC, $MGBLSC, $MGBLSC_64

Condition Values Returned

SS$_CREATED	Global section has been created.
SS$_CREATED_SHPT	Global section has been created with shared page tables.
SS$_ACCVIO	The gs_name_64 descriptor cannot be read by the caller, or the reserved_length_64 argument was specified as a nonzero value and cannot be written by the caller.
SS$_DUPLNAM	A global section of the same name already exists; a new global section was not created.
SS$_GPTFULL	There is no more room in the system global page table to set up page table entries for the global section or for the shared page tables.
SS$_GSDFULL	There is no more room in the system space allocated to maintain control information for global sections.
SS$_IVLOGNAM	The specified global section name has a length of 0 or has more than 43 characters.
SS$_IVPROTECT	The protection argument format is invalid.
SS$_IVSECFLG	An invalid flag, a reserved flag, or an invalid combination of flags was specified.
SS$_IVSECIDCTL	The match control field of the global section identification is invalid.
SS$_LEN_NOTPAGMULT	The length_64 argument is not a multiple of CPU-specific pages.
SS$_MRES_PFNSMALL	Preallocated, contiguous, aligned physical memory specified in the Reserved Memory Registry is smaller than the length specified for the global section by the length_64 argument.
SS$_NOMEMRESID	The process attempted to create a memory-resident section but was not holding the correct identifier (VMS$MEM_RESIDENT_USER).
SS$_NOPRMGBL	The process does not have the privileges to create or delete a permanent group global section (PRMGBL).
SS$_NOSYSGBL	The process does not have the privileges to create or delete a system global section (SYSGBL).
SS$_SECTBLFUL	There are no entries available in the system global section table for the global section or for the shared page tables.
SS$_TOOMANYLNAM	The logical name translation of the gs_name_64 argument exceeded the allowed depth of 10.

On Alpha systems, creates a permanent global disk file section to which processes can map.

This service accepts 64-bit addresses.

Format

SYS$CREATE_GFILE gs_name_64 ,ident_64 ,file_offset_64 ,length_64 ,chan ,acmode ,flags ,return_length_64 [,fault_cluster]

C Prototype

int sys$create_gfile (void *gs_nam_64, struct _secid *ident_64, unsigned __int64 file_offset_64, unsigned __int64 length_64, unsigned short int chan, unsigned int acmode, unsigned int flags, 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 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 two 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.

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 and 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.

file_offset_64

OpenVMS usage:	byte offset
type:	quadword (unsigned)
access:	read only
mechanism:	by value

Byte offset into the file that marks the beginning of the section. The file_offset_64 argument is a quadword containing this number. If you do not specify the file_offset_64 argument or specify it as 0, the section is created beginning with the first byte in the file.

The file_offset_64 argument must be a multiple of virtual disk blocks.

length_64

OpenVMS usage:	byte count
type:	quadword (unsigned)
access:	read only
mechanism:	by value

Length, in bytes, of the global disk file section to be created. The length specified must be 0 or a multiple of virtual disk blocks. If the length specified is 0 or extends beyond end-of-file (EOF), the global disk file section is created up to and including the virtual block number that contains EOF.

chan

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

Number of the channel on which the file has been accessed. The chan argument is a longword containing this number. The access mode at which the channel was opened must be equal to or less privileged than the access mode of the caller.

You can use the OpenVMS Record Management Services (RMS) macro $OPEN to access a file; the file options parameter in the file access block must indicate a user file open (UFO keyword).

acmode

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

Access mode that is to be the owner of the pages created during the mapping. The acmode argument is a longword containing the access mode.

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

flags

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

Flag mask specifying the type of global section to be created as well as its characteristics. The flags argument is a longword bit vector in which each bit corresponds to a flag. The $SECDEF macro and the SECDEF.H file define a symbolic name for each flag. You construct the flags argument by performing a logical OR operation on the symbol names for all desired flags. The following table describes each flag that is valid for the $CREATE_GFILE service:

Flag	Description
SEC$M_CRF	Pages are copy-on-reference. By default, pages are shared.
SEC$M_DZRO	Pages are demand-zero pages. By default, they are not zeroed when copied. Note that SEC$M_DZRO and SEC$M_CRF cannot both be set and that SEC$M_DZRO set and SEC$M_WRT clear is an invalid combination.
SEC$M_GBL	Pages form a global section. By default, this flag is always present in this service and cannot be disabled.
SEC$M_PERM	Global section is permanent. By default, this flag is always present in this service and cannot be disabled.
SEC$M_SYSGBL	Pages form a system global section. By default, pages form a group global section.
SEC$M_WRT	Pages form a read/write section. By default, pages form a read-only section.

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