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CentOS 7.0 - man page for mremap (centos section 2)

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

NAME
       mremap - remap a virtual memory address

SYNOPSIS
       #define _GNU_SOURCE	   /* See feature_test_macros(7) */
       #include <sys/mman.h>

       void *mremap(void *old_address, size_t old_size,
		    size_t new_size, int flags, ... /* void *new_address */);

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.  An optional fifth argument, new_address, may be provided; see the description
       of MREMAP_FIXED below.

       In Linux the memory is divided into pages.  A user process has  (one  or)  several  linear
       virtual	memory	segments.   Each  virtual memory segment 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 incor-
       rectly (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(3).

       The flags bit-mask argument may be 0, or include the following flag:

       MREMAP_MAYMOVE
	      By default, if there is not sufficient space to expand a	mapping  at  its  current
	      location,  then mremap() fails.  If this flag is specified, then the kernel is per-
	      mitted to relocate the mapping to a new virtual address, if necessary.  If the map-
	      ping  is	relocated,  then  absolute  pointers into the old mapping location become
	      invalid (offsets relative  to  the  starting  address  of  the  mapping  should  be
	      employed).

       MREMAP_FIXED (since Linux 2.3.31)
	      This  flag serves a similar purpose to the MAP_FIXED flag of mmap(2).  If this flag
	      is specified, then mremap() accepts  a  fifth  argument,	void *new_address,  which
	      specifies  a page-aligned address to which the mapping must be moved.  Any previous
	      mapping at the address range specified by new_address and new_size is unmapped.  If
	      MREMAP_FIXED is specified, then MREMAP_MAYMOVE must also be specified.

       If  the	memory segment specified by old_address and old_size is locked (using mlock(2) or
       similar), then this lock is maintained when the segment is resized and/or relocated.  As a
       consequence, the amount of memory locked by the process may change.

RETURN VALUE
       On success mremap() returns a pointer to the new virtual memory area.  On error, the value
       MAP_FAILED (that is, (void *) -1) is returned, and errno is set appropriately.

ERRORS
       EAGAIN The caller tried to expand a memory segment that is locked, but this was not possi-
	      ble without exceeding the RLIMIT_MEMLOCK resource limit.

       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.

       EINVAL An invalid argument was given.  Possible	causes	are:  old_address  was	not  page
	      aligned;	a value other than MREMAP_MAYMOVE or MREMAP_FIXED was specified in flags;
	      new_size was zero; new_size or new_address was invalid; or the  new  address  range
	      specified by new_address and new_size overlapped the old address range specified by
	      old_address and old_size; or MREMAP_FIXED was  specified	without  also  specifying
	      MREMAP_MAYMOVE.

       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.

CONFORMING TO
       This call is Linux-specific, and should not be used in programs intended to be portable.

NOTES
       Prior  to version 2.4, glibc did not expose the definition of MREMAP_FIXED, and the proto-
       type for mremap() did not allow for the new_address argument.

SEE ALSO
       brk(2), getpagesize(2), getrlimit(2), mlock(2), mmap(2), sbrk(2), malloc(3), realloc(3)

       Your favorite text book on operating systems for more information on paged  memory  (e.g.,
       Modern  Operating  Systems  by  Andrew  S. Tanenbaum, Inside Linux by Randolf Bentson, The
       Design of the UNIX Operating System by Maurice J. Bach)

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux					    2010-06-10					MREMAP(2)


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