VMF(3)              UNIX Programmer's Manual               VMF(3)



NAME
     vminit, vmopen, vmclose, vmmapseg, vmmodify, vmlock, vmun-
     lock, vmclrseg, vmflush, - disk based virtual memory rou-
     tines

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);





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VMF(3)              UNIX Programmer's Manual               VMF(3)



     void vmflush();

     void vmclose(space);
          struct    vspace *space;



















































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VMF(3)              UNIX Programmer's Manual               VMF(3)



DESCRIPTION
     This library provides a standard set of routines for manag-
     ing 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.

     _v_m_i_n_i_t - 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.

     _v_m_o_p_e_n - 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 vir-
     tual 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 (per-
     manent) file.

     _v_m_c_l_o_s_e - 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.

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

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

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

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

     _v_m_c_l_r_s_e_g - This routine clears the user data area (page) of
     the specified segment buffer.  _v_m_f_l_u_s_h - This routine simply
     swaps out all segments that are marked as modified.





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VMF(3)              UNIX Programmer's Manual               VMF(3)



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 _v_i_r_t_u_a_l _a_d_d_r_e_s_s crosses
     page/segment boundaries and perform a _v_m_m_a_p_s_e_g call.

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











































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