vdb

Name

clbvdb, opbvdb, rdvdb, savvdb, wrvdb — Paged low-level input/output system

Synopsis

subroutine clbvdb(handle,0,0,0,status)
integer*4 handle
integer*4 status

subroutine opbvdb(handle,fname,lbuf,dummy,lpage,iopen,status)
integer*4 handle
character*(*) fname
integer*4 lbuf
integer*4 lpage
integer*4 iopen
integer*4 status

subroutine rdvdb(handle,ipos,buffer,size,status)
integer*4 handle
integer*4 ipos
character*(*) buffer
integer*4 size
integer*4 status

subroutine savvdb(handle,status)
integer*4 handle
integer*4 status

subroutine wrvdb(handle,ipos,buffer,size,status)
integer*4 handle
integer*4 ipos
character*(*) buffer
integer*4 size
integer*4 status

Description

The MemCom paging system consists of a functions for emulating a paging mechanism by transferring data from the user space via a buffer to the database (and vice versa). Data transaction is completely transparent to the user.

If a file is opened in paged mode, i.e by calling opbvdb, the MemCom system tables will be ignored. Any application which accesses MemComs should therefore make use of the wtwadb and putwadb or rdwadb and getwadb DB system calls. The following functions are available:

clbvdb closes the paged input/output file. The pages in the buffer are copied to their destination pages on the database.
opbvdb opens a paged input/output file for access. The file handle, file name, buffer address, buffer length and page length are specified.
rdvdb reads raw data arrays from the database and transfer them to the user space. Data are either copied from the file to the buffer and to the user space (page fault), or moved from the buffer to the user space (data already in the page buffer).
savvdb saves the content of the page buffer.
wrvdb writes raw data from the user area to the paged input/output file. Data are moved to the buffer and copied to the database if one or more page faults become necessary.

Note: These functions work with word addresses (not byte addresses) and starting at word count 1. Thus, they are compatible with MemCom 6. Nevertheless they should not be use in new applications, since addresses are now based on bytes, and the byte count starts at address 0.

Parameters

handle: Database handle (input). The file handle handle may not exceed the maximum number of simultaneously open databases.
fname: File name (input).
lbuf: Paged input/output buffer size counted in integer*4 words (input).
dummy: Dummy variable for compatibility with version 6 (input).
lpage: Length of one page counted in integer*4 words (input).
iopen: File open code (input/output).
ipos: integer*4 word address on file of data to be transferred (input).
buffer: Buffer containing data to be transferred (void, i).
size: Number of integer*4 words to be read or written (input).
status: Status code returned (output). Upon successful completion of the operation, the status value 0 is returned. A negative value is returned, if an error has been detected. A positive value is returned, if a warning has been issued. See MemCom error codes.