@node _go32_info_block, dpmi
@vindex _go32_info_block
@tindex Go32_Info_Block@r{ type}
@subheading Syntax

@example
#include <go32.h>

extern __Go32_Info_Block _go32_info_block;
@end example

@subheading Description

The go32 information block is a mechanism for @file{go32} to pass
information to the application.  Some of this information is generally
useful, such as the pid or the transfer buffer, while some is used
internally to @file{libc.a} only. 

The structure has this format:

@example
typedef struct @{
  unsigned long  size_of_this_structure_in_bytes;
  unsigned long  linear_address_of_primary_screen;
  unsigned long  linear_address_of_secondary_screen;
  unsigned long  linear_address_of_transfer_buffer;
  unsigned long  size_of_transfer_buffer;
  unsigned long  pid;
  unsigned char  master_interrupt_controller_base;
  unsigned char  slave_interrupt_controller_base;
  unsigned short selector_for_linear_memory;
  unsigned long  linear_address_of_stub_info_structure;
  unsigned long  linear_address_of_original_psp;
  unsigned short run_mode;
  unsigned short run_mode_info;
@} Go32_Info_Block;
@end example

The linear address fields provide values that are suitable for
@code{dosmemget}, @code{dosmemput}, and @code{movedata}.  The
selector_for_linear_memory is suitable for @code{<sys/farptr.h>}
selector parameters.

Due to the length of these fields, and their popularity, the following
macros are available:

@table @code

@item _dos_ds

This expands to _go32_info_block.selector_for_linear_memory

@item __tb

This expands to _go32_info_block.linear_address_of_transfer_buffer

@item __tb_size

This expands to _go32_info_block.size_of_transfer_buffer

@end table

The @code{run_mode} field indicates the mode that the program is running
in.  The following modes are defined:

@table @code

@item _GO32_RUN_MODE_UNDEF

This indicates that the extender did not (or could not) determine or
provide the mode information.  The most probable reason is that it's an
older extender that does not support this field.  The program should not
assume anything about the run mode if it is this value. 

@item _GO32_RUN_MODE_RAW

This indicates that no CPU manager is being used, and no XMS manager is
present.  The CPU is being managed directly from the extender, and
memory was allocated from the extended memory pool. 

@item _GO32_RUN_MODE_XMS

This indicates that the extender is managing the CPU, but an XMS driver
is managing the memory pool. 

@item _GO32_RUN_MODE_VCPI

This indicates that a VCPI server (like @code{emm386} or @code{qemm}) is
managing both the CPU and the memory. 

@item _GO32_RUN_MODE_DPMI

This indicates that a DPMI server (like @code{qdpmi} or Windows) is
managing both the CPU and memory.  Programs may rely on this value
to determine if it is safe to use DPMI 0.9 functions.

If this value is set, the @code{run_mode_info} field has the DPMI
specification version, in hex, shifted eight bits.  For example, DPMI
0.9 has 0x005A in the @code{run_mode_info} field. 

@end table

Note that the program should not assume that the value will be one of
the listed values.  If the program is running with an extender that
provides some other mode (say, a newly released extender) then the
program should be able to handle that case gracefully. 

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
dosmemget(_go32_info_block.linear_address_of_primary_screen,
          80*25*2, buf);
@end example