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Manpage of MREMAP

MREMAP

Index
 

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

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

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

The fIflagsfR 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.

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

 

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 fBmremapfR returns a pointer to the new virtual memory area. On error, the value MAP_FAILED (that is, (void *) -1) is returned, and fIerrnofR is set appropriately.

 

ERRORS

EINVAL
An invalid argument was given. Most likely fIold_addressfR was not page aligned.
EFAULT
"Segmentation fault." Some address in the range fIold_addressfP to fIold_addressfP+fIold_sizefP 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 fIflagsfP. 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. (fIModern Operating SystemsfR by Andrew S. Tannenbaum, fIInside LinuxfR by Randolf Bentson, fIThe Design of the UNIX Operating SystemfR by Maurice J. Bach.)


 

Index

NAME
SYNOPSIS
DESCRIPTION
FLAGS
RETURN VALUE
ERRORS
NOTES
CONFORMING TO
SEE ALSO