mirror of https://github.com/mkerrisk/man-pages
192 lines
6.1 KiB
Groff
192 lines
6.1 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
|
|
.\"
|
|
.\" Copyright (c) 1996 Tom Bjorkholm <tomb@mydata.se>
|
|
.\"
|
|
.\" This is free documentation; you can redistribute it and/or
|
|
.\" modify it under the terms of the GNU General Public License as
|
|
.\" published by the Free Software Foundation; either version 2 of
|
|
.\" the License, or (at your option) any later version.
|
|
.\"
|
|
.\" The GNU General Public License's references to "object code"
|
|
.\" and "executables" are to be interpreted as the output of any
|
|
.\" document formatting or typesetting system, including
|
|
.\" intermediate and printed output.
|
|
.\"
|
|
.\" This manual is distributed in the hope that it will be useful,
|
|
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
.\" GNU General Public License for more details.
|
|
.\"
|
|
.\" You should have received a copy of the GNU General Public
|
|
.\" License along with this manual; if not, write to the Free
|
|
.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
|
|
.\" USA.
|
|
.\"
|
|
.\" 1996-04-11 Tom Bjorkholm <tomb@mydata.se>
|
|
.\" First version written (1.3.86)
|
|
.\" 1996-04-12 Tom Bjorkholm <tomb@mydata.se>
|
|
.\" Update for Linux 1.3.87 and later
|
|
.\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
|
|
.\"
|
|
.TH MREMAP 2 2005-09-13 "Linux 2.6.13" "Linux Programmer's Manual"
|
|
.SH NAME
|
|
mremap \- re-map a virtual memory address
|
|
.SH SYNOPSIS
|
|
.B #define _GNU_SOURCE
|
|
.br
|
|
.B #include <unistd.h>
|
|
.br
|
|
.B #include <sys/mman.h>
|
|
.sp
|
|
.BI "void * mremap(void *" old_address ", size_t " old_size
|
|
.BI ", size_t " new_size ", unsigned long " flags );
|
|
.fi
|
|
.SH DESCRIPTION
|
|
\fBmremap\fR() expands (or shrinks) an existing memory mapping, potentially
|
|
moving it at the same time (controlled by the \fIflags\fR argument and
|
|
the available virtual address space).
|
|
|
|
\fIold_address\fR is the old address of the virtual memory block that you
|
|
want to expand (or shrink). Note that \fIold_address\fR has to be page
|
|
aligned. \fIold_size\fR is the old size of the
|
|
virtual memory block. \fInew_size\fR is the requested size of the
|
|
virtual memory block after the resize.
|
|
|
|
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 incorrectly (e.g.,
|
|
writing to a read-only segment). Accessing virtual memory outside of the
|
|
segments will also cause a segmentation violation.
|
|
|
|
\fBmremap\fR() uses the Linux page table scheme.
|
|
\fBmremap\fR() changes the
|
|
mapping between virtual addresses and memory pages. This can be used to
|
|
implement a very efficient \fBrealloc\fR().
|
|
|
|
The \fIflags\fR bit-mask argument may be 0, or include the following flag:
|
|
.TP
|
|
.B MREMAP_MAYMOVE
|
|
By default, if there is not sufficient space to expand a mapping
|
|
at its current location, then
|
|
.BR mremap ()
|
|
fails.
|
|
If this flag is specified, then the kernel is permitted to
|
|
relocate the mapping to a new virtual address, if necessary.
|
|
If the mapping is relocated,
|
|
then absolute pointers into the old mapping location
|
|
become invalid (offsets relative to the starting address of
|
|
the mapping should be employed).
|
|
.TP
|
|
.BR MREMAP_FIXED " (since Linux 2.3.31)"
|
|
This flag serves a similar purpose to the
|
|
.B MAP_FIXED
|
|
flag of
|
|
.BR mmap (2).
|
|
If this flag is specified, then
|
|
.BR mremap ()
|
|
accepts a fifth argument,
|
|
.IR "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
|
|
.I new_address
|
|
and
|
|
.I new_size
|
|
is unmapped.
|
|
If
|
|
.B MREMAP_FIXED
|
|
is specified, then
|
|
.BR MREMAP_MAYMOVE
|
|
must also be specified.
|
|
.PP
|
|
If the memory segment specified by
|
|
.I old_address
|
|
and
|
|
.I old_size
|
|
is locked (using
|
|
.BR mlock ()
|
|
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.
|
|
.SH "RETURN VALUE"
|
|
On success \fBmremap\fR() returns a pointer to the new virtual memory area.
|
|
On error, the value
|
|
.B MAP_FAILED
|
|
(that is, (void *) \-1) is returned, and \fIerrno\fR is set appropriately.
|
|
.SH ERRORS
|
|
.TP
|
|
.B EAGAIN
|
|
The caller tried to expand a memory segment that is locked,
|
|
but this was not possible without exceeding the
|
|
RLIMIT_MEMLOCK resource limit.
|
|
.TP
|
|
.B EFAULT
|
|
"Segmentation fault." Some address in the range
|
|
\fIold_address\fP to \fIold_address\fP+\fIold_size\fP 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.
|
|
.TP
|
|
.B EINVAL
|
|
An invalid argument was given.
|
|
Possible causes are: \fIold_address\fR was not
|
|
page aligned; a value other than
|
|
.B MREMAP_MAYMOVE
|
|
or
|
|
.B MREMAP_FIXED
|
|
was specified in
|
|
.IR flags ;
|
|
.I new_size
|
|
was zero;
|
|
.I new_size
|
|
or
|
|
.I new_address
|
|
was invalid;
|
|
or the new address range specified by
|
|
.I new_address
|
|
and
|
|
.I new_size
|
|
overlapped the old address range specified by
|
|
.I old_address
|
|
and
|
|
.IR old_size ;
|
|
or
|
|
.B MREMAP_FIXED
|
|
was specified without also specifying
|
|
.BR MREMAP_MAYMOVE .
|
|
.TP
|
|
.B ENOMEM
|
|
The memory area cannot be expanded at the current virtual address, and the
|
|
.B MREMAP_MAYMOVE
|
|
flag is not set in \fIflags\fP.
|
|
Or, there is not enough (virtual) memory available.
|
|
.SH NOTES
|
|
Prior to version 2.4, glibc did not expose the definition of
|
|
.BR MREMAP_FIXED ,
|
|
and the prototype for
|
|
.BR mremap ()
|
|
did not allow for the
|
|
.I new_address
|
|
argument.
|
|
.SH "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)
|
|
.BR mremap (2)
|
|
call with completely different semantics.
|
|
.SH "SEE ALSO"
|
|
.BR brk (2),
|
|
.BR getpagesize (2),
|
|
.BR getrlimit (2),
|
|
.BR mlock (2),
|
|
.BR mmap (2),
|
|
.BR sbrk (2),
|
|
.BR malloc (3),
|
|
.BR realloc (3)
|
|
.P
|
|
Your favorite OS text book for more information on paged memory.
|
|
(\fIModern Operating Systems\fR by Andrew S. Tannenbaum,
|
|
\fIInside Linux\fR by Randolf Bentson,
|
|
\fIThe Design of the UNIX Operating System\fR by Maurice J. Bach.)
|