Penguin
Recent Changes
Annotated edit history of mremap(2) version 2, including all changes. View license author blame.
Rev Author # Line
1 perry 1 !!NAME
2 mremap - re-map a virtual memory address
3 !!SYNOPSIS
4
2 PerryLorier 5 __#include <unistd.h>__
6 __#include <sys/mman.h>__
1 perry 7
2 PerryLorier 8 __void * mremap(void *__ ''old_address''__, size_t__ ''old_size'' __, size_t__ ''new_size''__, unsigned long__ ''flags''__);__
1 perry 9 !!DESCRIPTION
2 PerryLorier 10 __mremap__ expands (or shrinks) an existing memory mapping, potentially moving it at the same time (controlled by the ''flags'' argument and the available virtual
1 perry 11 address space).
12
2 PerryLorier 13 ''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''
14 is the old size of the virtual memory block. ''new_size'' is the requested size of the virtual memory block after the
1 perry 15 resize.
16
17 The ''flags'' argument is a bitmap of flags.
18
2 PerryLorier 19 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
1 perry 20 cause a segmentation violation.
21
2 PerryLorier 22 __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
23 efficient __realloc__.
1 perry 24
25 !!FLAGS
2 PerryLorier 26 ;__MREMAP_MAYMOVE__: indicates if the operation should fail, or change the virtual address if the resize cannot be done at the current virtual address.
1 perry 27 !!RETURN VALUE
2 PerryLorier 28 On success __mremap__ returns a pointer to the new virtual memory area. On error, -1 is returned, and ''errno'' is set appropriately.
1 perry 29 !!ERRORS
2 PerryLorier 30 ;[EINVAL]: An invalid argument was given. Most likely ''old_address'' was not page aligned.
31 ;[EFAULT]: 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.
32 ;[EAGAIN]: The memory segment is locked and cannot be re-mapped.
33 ;[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.
1 perry 34
35 !!CONFORMING TO
2 PerryLorier 36 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
37 different semantics.
1 perry 38
39 !!SEE ALSO
2 PerryLorier 40 getpagesize(2), realloc(3), malloc(3), brk(2), sbrk(2), mmap(2)
1 perry 41
2 PerryLorier 42 Your favorite OS text book for more information on paged memory. (''Modern Operating Systems'' by Andrew S. Tannenbaum, ''Inside Linux'' by Randolf Bentson, ''The
43 Design of the UNIX Operating System'' by Maurice J. Bach.)
This page is a man page (or other imported legacy content). We are unable to automatically determine the license status of this page.

PHP Warning

lib/blame.php:177: Warning: Invalid argument supplied for foreach() (...repeated 6 times)