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DPMI Overview
=============

     extern unsigned short __dpmi_error;

For most functions, the error returned from the DPMI server is stored
in this variable.

     typedef struct {
       unsigned short offset16;
       unsigned short segment;
     } __dpmi_raddr;

This structure is used to hold a real-mode address, which consists of a
segment:offset pair.

     typedef struct {
       unsigned long  offset32;
       unsigned short selector;
     } __dpmi_paddr;

This structure is used to hold a protected-mode address, which consists
of a selector:offset pair.

     typedef struct {
       unsigned long handle;                     /* 0, 2 */
       unsigned long size;        /* or count */       /* 4, 6 */
       unsigned long address;              /* 8, 10 */
     } __dpmi_meminfo;

This structure is used by many functions that need to refer to blocks
of 32-bit memory.  The `size' field doubles as a count for those
operations that want a count of something, or return a count.

     typedef union {
       struct {
         unsigned long edi;
         unsigned long esi;
         unsigned long ebp;
         unsigned long res;
         unsigned long ebx;
         unsigned long edx;
         unsigned long ecx;
         unsigned long eax;
       } d;
       struct {
         unsigned short di, di_hi;
         unsigned short si, si_hi;
         unsigned short bp, bp_hi;
         unsigned short res, res_hi;
         unsigned short bx, bx_hi;
         unsigned short dx, dx_hi;
         unsigned short cx, cx_hi;
         unsigned short ax, ax_hi;
         unsigned short flags;
         unsigned short es;
         unsigned short ds;
         unsigned short fs;
         unsigned short gs;
         unsigned short ip;
         unsigned short cs;
         unsigned short sp;
         unsigned short ss;
       } x;
       struct {
         unsigned char edi[4];
         unsigned char esi[4];
         unsigned char ebp[4];
         unsigned char res[4];
         unsigned char bl, bh, ebx_b2, ebx_b3;
         unsigned char dl, dh, edx_b2, edx_b3;
         unsigned char cl, ch, ecx_b2, ecx_b3;
         unsigned char al, ah, eax_b2, eax_b3;
       } h;
     } __dpmi_regs;

This structure is used by functions that pass register information,
such as simulating real-mode calls.

     typedef struct {
       unsigned char  major;
       unsigned char  minor;
       unsigned short flags;
       unsigned char  cpu;
       unsigned char  master_pic;
       unsigned char  slave_pic;
     } __dpmi_version_ret;

This structure is used to return version information to the program.

     typedef struct {
       unsigned long largest_available_free_block_in_bytes;
       unsigned long maximum_unlocked_page_allocation_in_pages;
       unsigned long maximum_locked_page_allocation_in_pages;
       unsigned long linear_address_space_size_in_pages;
       unsigned long total_number_of_unlocked_pages;
       unsigned long total_number_of_free_pages;
       unsigned long total_number_of_physical_pages;
       unsigned long free_linear_address_space_in_pages;
       unsigned long size_of_paging_file_partition_in_pages;
       unsigned long reserved[3];
     } __dpmi_free_mem_info;

This structure is used to return information about the state of virtual
memory in the system.

     typedef struct {
       unsigned long total_allocated_bytes_of_physical_memory_host;
       unsigned long total_allocated_bytes_of_virtual_memory_host;
       unsigned long total_available_bytes_of_virtual_memory_host;
       unsigned long total_allocated_bytes_of_virtual_memory_vcpu;
       unsigned long total_available_bytes_of_virtual_memory_vcpu;
       unsigned long total_allocated_bytes_of_virtual_memory_client;
       unsigned long total_available_bytes_of_virtual_memory_client;
       unsigned long total_locked_bytes_of_memory_client;
       unsigned long max_locked_bytes_of_memory_client;
       unsigned long highest_linear_address_available_to_client;
       unsigned long size_in_bytes_of_largest_free_memory_block;
       unsigned long size_of_minimum_allocation_unit_in_bytes;
       unsigned long size_of_allocation_alignmentunit_in_bytes;
       unsigned long reserved[19];
     } __dpmi_memory_info;

This is also used to return memory information, but by a different
function.

     typedef struct {
       unsigned long data16[2];
       unsigned long code16[2];
       unsigned short ip;
       unsigned short reserved;
       unsigned long data32[2];
       unsigned long code32[2];
       unsigned long eip;
     } __dpmi_callback_info;

This structure is used to install TSR programs.

     typedef struct {
       unsigned long size_requested;
       unsigned long size;
       unsigned long handle;
       unsigned long address;
       unsigned long name_offset;
       unsigned short name_selector;
       unsigned short reserved1;
       unsigned long reserved2;
     } __dpmi_shminfo;

This structure is used to manipulate shared memory regions.