HP OpenVMS Systems Documentation

HP OpenVMS System Services Reference Manual

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.

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

When a section is mapped at creation time, the match control field is ignored.

If you do not specify the ident argument or specify it as 0 (the default), the version number and match control fields default to 0.

relpag

On Alpha and I64 systems, the relpag argument is interpreted as an index into the section file, measured in pagelets for a file-backed section or in CPU-specific pages for a PFN-mapped section.

On Alpha or I64 and VAX systems, you use this argument only for global sections. If you do not specify the relpag argument or specify it as 0 (the default), the global section is mapped beginning with the first virtual block in the file.

chan

The file must have been accessed with the OpenVMS RMS macro $OPEN; the file options parameter (FOP) in the FAB must indicate a user file open (UFO keyword). The access mode at which the channel was opened must be equal to or less privileged than the access mode of the caller.

pagcnt

On Alpha and I64 systems, the smallest allocation is an Alpha or I64 page, which is 8192 bytes. When requesting pagelets, the size requested is a multiple of 512 bytes, but the actual allocation is rounded to 8192. For example, when requesting 17 pagelets, the allocation is for two Alpha or I64 pages, 16384 bytes.

On Alpha and I64 systems, if the SEC$M_PFNMAP flag bit is set, the pagcnt argument is interpreted as CPU-specific pages, not as pagelets.

On Alpha or I64 and VAX systems, the specified page count is compared with the number of blocks in the section file; if they are different, the lower value is used. If you do not specify the page count or specify it as 0 (the default), the size of the section file is used. However, for physical page frame sections, this argument must not be 0.

vbn

If you specified page frame number mapping (by setting the SEC$M_PFNMAP flag), the vbn argument specifies the CPU-specific page frame number where the section begins in memory.

Table SYS-21 shows which arguments are required and which are optional for three different uses of the $CRMPSC service.

prot

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.

Protection is taken from the system or group global section template for page file or PFN global sections if the prot argument is not specified.

pfc

On Alpha and I64 systems, this argument is not used for page file sections or physical page frame sections. The pfc argument is rounded up to CPU-specific pages. That is, at least 16 pagelets (on an Alpha or I64 system with an 8KB page size) will be mapped for each physical page. The system cannot map less than one physical page.

On VAX systems, this argument is not used for page file sections or physical page frame sections.

Description

The Create and Map Section service allows a process to associate (map) a section of its address space with (1) a specified section of a file (a disk file section) or (2) specified physical addresses represented by page frame numbers (a page frame section). This service also allows the process to create either type of section and to specify that the section be available only to the creating process (private section) or to all processes that map to it (global section).

Creating a disk file section involves defining all or part of a disk file as a section. Mapping a disk file section involves making a correspondence between virtual blocks in the file and pages (on VAX systems) or pagelets (on Alpha and I64 systems) in the caller's virtual address space. If the $CRMPSC service specifies a global section that already exists, the service maps it.

Any section created is created as entire pages. Refer to the memory management section in the OpenVMS Programming Concepts Manual.

Depending on the actual operation requested, certain arguments are required or optional. Table SYS-21 summarizes how the $CRMPSC service interprets the arguments passed to it and under what circumstances it requires or ignores arguments.

The $CRMPSC service returns the virtual addresses of the virtual address space created in the retadr argument, if specified. The section is mapped from a low address to a high address, whether the section is mapped in the program or control region.

If an error occurs during the mapping of a global section, the retadr argument, if specified, indicates the pages that were successfully mapped when the error occurred. If no pages were mapped, the value of the longwords is indeterminate. In this case, either both longwords of the retadr argument will contain the value --1, or the value of the longwords will be unaltered.

The SEC$M_PFNMAP flag setting identifies the memory for the section as starting at the page frame number specified in the vbn argument and extending for the number of CPU-specific pages specified in the pagcnt argument. Setting the SEC$M_PFNMAP flag places restrictions on the following arguments:

Argument	Restriction
chan	Must be 0
pagcnt	Must be specified; cannot be 0
vbn	Specifies first page frame to be mapped
pfc	Does not apply
SEC$M_CRF	Must be 0
SEC$M_DZRO	Must be 0
SEC$M_PERM	Must be 1 if the flags SEC$M_GBL or SEC$M_SYSGBL are set

Setting the SEC$M_PAGFIL flag places the following restrictions on the following flags:

Flag	Restriction
SEC$M_CRF	Must be 0
SEC$M_DZRO	Assumed to be 0
SEC$M_GBL	Must be 1
SEC$M_PFNMAP	Must be 0
SEC$M_WRT	Assumed to be 0

The flags argument bits 4 through 13 and 18 through 31 must be 0.

If the global section is mapped to a file (neither SEC$M_PAGFIL nor SEC$M_PFNMAP is set), the security profile of the file is used to determine access to the global section.

On VAX systems, by default, the initial security profile created for a page file or PFN global section is taken from the group global section template. If the SEC$M_SYSGBL flag is set, the profile is taken from the system global section template. The owner is then set to the process UIC. If the prot argument is nonzero, it replaces the protection mask from the template.

On Alpha or I64 and VAX systems, the flag bit SEC$M_WRT applies only to the way in which the newly created section is mapped. For a file to be made writable, the channel used to open the file must allow write access to the file.

If the flag bit SEC$M_SYSGBL is set, the flag bit SEC$M_GBL must be set also.

Required Access or Privileges

If $CRMPSC specifies a global section and the SS$_NOPRIV condition value is returned, the process does not have the required privilege to create that section. To create global sections, the process must have the following privileges:

• SYSGBL privilege to create a system global section
• PRMGBL privilege to create a permanent global section
• PFNMAP privilege to create a page frame section
• SHMEM privilege to create a global section in memory shared by multiple processors (VAX only)

Note that you do not need PFNMAP privilege to map an existing page frame section.

Required Quota

If the section pages are copy-on-reference, the process must have sufficient paging file quota (PGFLQUOTA). The systemwide number of global page file pages is limited by the system parameter GBLPAGFIL.

Related Services

$ADJSTK, $ADJWSL, $CRETVA, $DELTVA, $DGBLSC, $EXPREG, $LCKPAG, $LKWSET, $MGBLSC, $PURGWS, $SETPRT, $SETSTK, $SETSWM, $ULKPAG, $ULWSET, $UPDSEC, $UPDSECW

Condition Values Returned

SS$_NORMAL	The service completed successfully. The specified global section already exists and has been mapped.
SS$_CREATED	The service completed successfully. The specified global section did not previously exist and has been created.
SS$_ACCVIO	The inadr argument, gsdnam argument, or name descriptor cannot be read by the caller; the inadr argument was omitted; or the retadr argument cannot be written by the caller.
SS$_ENDOFFILE	The starting virtual block number specified is beyond the logical end-of-file, or the value in the relpag argument is greater than or equal to the actual size of the global section.
SS$_EXBYTLM	The process has exceeded the byte count quota; the system was unable to map the requested file.
SS$_EXGBLPAGFIL	The process has exceeded the systemwide limit on global page file pages; no part of the section was mapped.
SS$_EXQUOTA	The process exceeded its paging file quota while creating copy-on-reference or page file backing store pages.
SS$_GPTFULL	There is no more room in the system global page table to set up page table entries for the section.
SS$_GSDFULL	There is no more room in the system space allocated to maintain control information for global sections.
SS$_ILLPAGCNT	The page count value is negative or is 0 for a physical page frame section.
SS$_INSFMEM	Not enough pages are available in the specified shared memory to create the section.
SS$_INSFWSL	The process's working set limit is not large enough to accommodate the increased size of the address space.
SS$_IVCHAN	An invalid channel number was specified, that is, a channel number of 0 or a number larger than the number of channels available.
SS$_IVCHNLSEC	The channel number specified is currently active.
SS$_IVLOGNAM	The specified global section name has a length of 0 or has more than 43 characters.
SS$_IVLVEC	The specified section was not installed using the /PROTECT qualifier.
SS$_IVSECFLG	An invalid flag, a reserved flag, a flag requiring a privilege you lack, or an invalid combination of flags was specified.
SS$_IVSECIDCTL	The match control field of the global section identification is invalid.
SS$_NOPRIV	The process does not have the privileges to create a system global section (SYSGBL) or a permanent group global section (PRMGBL). The process does not have the privilege to create a section starting at a specific physical page frame number (PFNMAP). The process does not have the privilege to create a global section in memory shared by multiple processors (SHMEM). A page in the input address range is in the system address space. The specified channel is not assigned or was assigned from a more privileged access mode.
SS$_NOSHPTS	A virtual address within a shared page table region was specified.
SS$_NOTFILEDEV	The device is not a file-oriented, random-access, or directory device.
SS$_NOWRT	The section cannot be written to because the flag bit SEC$M_WRT is set, the file is read only, and the flag bit SEC$M_CRF is not set.
SS$_PAGOWNVIO	A page in the specified input address range is owned by a more privileged access mode.
SS$_SECREFOVF	The maximum number of references for a global section has been reached (2,147,483,647).
SS$_SECTBLFUL	There are no entries available in the system global section table or in the process section table.
SS$_TOOMANYLNAM	The logical name translation of the gsdnam argument exceeded the allowed depth.
SS$_VA_IN_USE	A page in the specified input address range is already mapped, and the flag SEC$M_NO_OVERMAP is set, or the existing underlying page cannot be deleted because it is associated with a buffer object.
SS$_VASFULL	The process's virtual address space is full; no space is available in the page tables for the pages created to contain the mapped global section.