VMF(3)							     Library Functions Manual							    VMF(3)

NAME

       vminit, vmopen, vmclose, vmmapseg, vmmodify, vmlock, vmunlock, vmclrseg, vmflush, - disk based virtual memory routines

SYNOPSIS

       #include <vmf.h>

       struct vspace {
	    int     v_fd;	    /* file for swapping */
	    off_t   v_foffset;	    /* offset for computing file addresses */
	    int     v_maxsegno;     /* number of segments in this space */
	    };

       struct	 vseg { 		   /* structure of a segment in memory */
	    struct    dlink	s_link;        /* for linking into lru list */
	    int  s_segno;	     /* segment number */
	    struct    vspace	*s_vspace;	/* which virtual space */
	    int  s_lock_count;
	    int     s_flags;
	    union
		 {
		 int  _winfo[WORDSPERSEG];     /* the actual segment */
		 char _cinfo[BYTESPERSEG];
		 } v_un;
	    };
       #define	 s_winfo   v_un._winfo
       #define	 s_cinfo   v_un._cinfo

       int  vminit(nseg);
	    int nseg;

       int  vmopen(space, filename);
	    struct vspace *space;
	    char *filename;

       struct	 vseg *vmmapseg(space, segno);
	    struct    vspace	*space;
	    int  segno;

       void vmlock(seg);
	    struct    vseg *seg;

       void vmunlock(seg);
	    struct    vseg *seg;

       void vmclrseg(seg);
	    struct    vseg *seg;

       void vmmodify(seg);

       void vmflush();

       void vmclose(space);
	    struct    vspace *space;

DESCRIPTION

       This  library  provides	a  standard set of routines for managing large virtual memory spaces.  It supports creation of multiple concurrent
       virtual spaces, mapping of virtual pages into real memory, a lock/unlock mechanism, and a capability to clear specified virtual pages.

       vminit - This routine initializes the virtual memory system by setting up the pool of in-memory segment	buffers.   The	argument  to  this
       function  is  the number of memory segments to allocate (typically 4 to 8 but can be higher as long as memory can be malloc'd).	It must be
       called before any other "libvmf" routine is called.

       vmopen - For each virtual space that a program uses, the program must allocate an instance of the space structure ('struct vspace').   This
       routine is used to initialize a virtual space structure using the specified address of a space structure and the name of the file that will
       serve as swap file for the space.  If the second argument is NULL an invisible temporary file is used rather than a named (permanent) file.

       vmclose - This routine is used to close the UNIX file descriptor associated with the swap file for a virtual space.  Any modified in-memory
       segments belonging to the specified address space are flushed to the paging file.

       vmmapseg -  This  routine  is the primary interface to the virtual memory mechanism.  It is executed with a specified virtual space address
       and a segment number (between 0 and 511), and returns a pointer to an in-memory page containing the specified segment.

       vmmodify - Whenever a program modifies the data of a segment, it is the program's responsibility to inform the virtual memory system of the
       modification.  This function is also available as a macro (VMMODIFY) for use in-line.

       vmlock -  This  routine increments the lock count of the specified segment buffer.  A buffer with a nonzero lock count is locked and cannot
       be swapped out.

       vmunlock - This routine decrements the lock count of the specified buffer.  It is a serious error to decrement the count below  zero  (lock
       underflow).

       vmclrseg - This routine clears the user data area (page) of the specified segment buffer.  vmflush - This routine simply swaps out all seg-
       ments that are marked as modified.

BUGS

       Not as transparent (or as fast) as a larger hardware address space.

       There is no automatic segment crossing capability, the application must check if a virtual address crosses page/segment boundaries and per-
       form a vmmapseg call.

SEE ALSO

       There is a nroff document (using the -ms macros) in the libvmf source directory which goes into more details about the vm functions.

4.3 Berkeley Distribution					September 24, 1993							    VMF(3)