MREMAP(2)						     Linux Programmer's Manual							 MREMAP(2)

NAME

       mremap - re-map a virtual memory address

SYNOPSIS

       #include <unistd.h>
       #include <sys/mman.h>

       void * mremap(void *old_address, size_t old_size , size_t new_size, unsigned long flags);

DESCRIPTION

       mremap  expands	(or  shrinks) an existing memory mapping, potentially moving it at the same time (controlled by the flags argument and the
       available virtual address space).

       old_address is the old address of the virtual memory block that you want to expand (or shrink).	Note  that  old_address  has  to  be  page
       aligned.  old_size  is  the  old  size  of  the virtual memory block.  new_size is the requested size of the virtual memory block after the
       resize.

       The flags argument is a bitmap of flags.

       In Linux the memory is divided into pages.  A user process has (one or) several linear virtual memory segments.	Each virtual  memory  seg-
       ment  has  one  or  more  mappings  to  real  memory pages (in the page table).	Each virtual memory segment has its own protection (access
       rights), which may cause a segmentation violation if the memory is accessed incorrectly (e.g., writing to a read-only segment).	 Accessing
       virtual memory outside of the segments will also cause a segmentation violation.

       mremap  uses  the  Linux  page  table  scheme.  mremap changes the mapping between virtual addresses and memory pages.  This can be used to
       implement a very efficient realloc.

FLAGS

       MREMAP_MAYMOVE
	      indicates if the operation should fail, or change the virtual address if the resize cannot be done at the current virtual address.

RETURN VALUE

       On success mremap returns a pointer to the new virtual memory area.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       EINVAL An invalid argument was given. Most likely old_address was not page aligned.

       EFAULT "Segmentation fault." Some address in the range old_address to old_address+old_size is an invalid virtual memory	address  for  this
	      process.	 You can also get EFAULT even if there exist mappings that cover the whole address space requested, but those mappings are
	      of different types.

       EAGAIN The memory segment is locked and cannot be re-mapped.

       ENOMEM The memory area cannot be expanded at the current virtual address, and the MREMAP_MAYMOVE flag is not set in flags.   Or,  there	is
	      not enough (virtual) memory available.

NOTES

       With  current  glibc  includes,	in  order  to  get  the  definition  of  MREMAP_MAYMOVE,  you  need to define _GNU_SOURCE before including
       <sys/mman.h>.

CONFORMING TO

       This call is Linux-specific, and should not be used in programs intended to  be	portable.   4.2BSD  had  a  (never  actually  implemented)
       mremap(2) call with completely different semantics.

SEE ALSO

       getpagesize(2), realloc(3), malloc(3), brk(2), sbrk(2), mmap(2)

       Your  favorite  OS text book for more information on paged memory.  (Modern Operating Systems by Andrew S. Tannenbaum, Inside Linux by Ran-
       dolf Bentson, The Design of the UNIX Operating System by Maurice J. Bach.)

Linux 1.3.87							    1996-04-12								 MREMAP(2)