@node mprotect, memory
@subheading Syntax

@example
#include <sys/types.h>
#include <sys/mman.h>

int mprotect(void *addr, size_t len, int prot);
@end example

@subheading Description

This function modifies the access protection of a memory region.  Protection
occurs in 4Kbyte regions (pages) aligned on 4Kbyte boundaries.  All pages 
in the region will be changed, so @var{addr} and @var{len} should be multiples 
of 4096.

The protection @var{prot} for each page is specified with the values:
  PROT_NONE  Region can not be touched (if or'ed is ignored).
  PROT_READ  Region can be read (can be or'ed with PROT_WRITE).
  PROT_WRITE Region can be written (implies read access).
  
This function is only supported on DPMI hosts which provide some V1.0 extensions
on V0.9 memory blocks.

@subheading Return Value

The function returns 0 if successful and the value -1 if all the pages 
could not be set.  

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
mprotect(readonly_buffer,8192,PROT_READ);
mprotect(guard_area,4096,PROT_NONE);
mprotect(NULL,4096,PROT_WRITE);	/* Let NULL pointers not generate exceptions */
@end example