2.11BSD/man/cat3/vmf.0
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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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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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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