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.\" Copyright (c) 1996 Tom Bjorkholm <tomb@mydata.se>
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.\" 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
.\"
.TH MREMAP 2 1996-04-12 "Linux 1.3.87" "Linux Programmer's Manual"
.SH NAME
mremap \- re-map a virtual memory address 
.SH SYNOPSIS
.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. 

The \fIflags\fR 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 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.

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

.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 memory segment is locked and cannot be re-mapped.
.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. Most likely \fIold_address\fR was not 
page aligned.
.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
With current glibc includes, in order to get the definition of
.BR MREMAP_MAYMOVE ,
you need to define _GNU_SOURCE before including <sys/mman.h>.
.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 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.)