==== FS_OPENPAGEFILE ====

**Purpose**

Creates/opens the paging file for the Pager.   

**Calling Sequence**

<code c>
int far pascal FS_OPENPAGEFILE(pFlags, pcMaxReq, pName, psffsi, psffsd,
                               usOpenMode, usOpenFlag, usAttr, Reserved)

unsigned long far * pFlag;
unsigned long far * pcMaxReq;
char far * pName;
struct sffsi far * psffsi;
struct sffsd far * psffsi;
unsigned short usOpenMode;
unsigned short usOpenFlag;
unsigned short usAttr;
unsigned long Reserved;
</code>

**Where**

//pFlag// is a pointer to a flag double word for passing of information between the pager and the file system.   

|//pFlag// == 0x00000001 |indicates first open of the page file. |
|//pFlag// == 0x00004000 |indicates physical addresses are required in the page list. |
|//pFlag// == 0x00008000 |indicates 16:16 virtual addresses are required in the page list. |

All other values are reserved.   

//pcMaxReq// is a pointer to a unsigned long where the FSD places the maximum request list length that can be managed by an enhanced strategy device driver.   

//pName// is a pointer to the ASCIIZ path and filename of the paging file.   

//psffsi// is a pointer to the file-system-independent portion of an open file instance.   

//psffsd// is a pointer to the file-system-dependent portion of an open file instance.   

//usOpenMode// indicates the desired sharing mode and access mode for the file handle.   

See OS/2 Version 2.0 Control Program Programming Reference for a description of the //OpenMode// parameter for //DosOpen//.   

//usOpenFlag// indicates the action taken when the file is present or absent.   

See OS/2 Version 2.0 Control Program Programming Reference for a description of the //usOpenFlag// parameter for //DosOpen//.   

//usAttr// are the OS/2 file attributes.   

//Reserved// is a double word parameter reserved for use in the future. 

**Remarks**

Enough information is provided for the FSD to perform a "normal" open/create call.   

Since a page file has special requirements about contiguity of its allocations, //FS_OPENPAGEFILE// must assure that any data sectors allocated are returned (Create call only). //FS_ALLOCATEPAGESPACE// will be called to handle file allocation.   

If the FSD cannot support the //FS_DOPAGEIO// (usually due to an disk device driver which does not support the Extended strategy entry point), the FSD can return zero (0) for *//pcMaxReq//. This tells the kernel file system that it must emulate //FS_DOPAGEIO//.   

The FSD can require either physical or virtual (16:16) addresses for subsequent calls to //FS_DOPAGEIO//. This allows an FSD to emulate //FS_DOPAGEIO// without having to worry about dealing with physical addresses.   

For a detailed description of the Extended Strategy request interface please see the OS/2 Version 2.0 Physical Device Driver Reference.