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!!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 __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. The ''flags'' 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. __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__. !!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 __mremap__ returns a pointer to the new virtual memory area. On error, -1 is returned, and ''errno'' is set appropriately. !!ERRORS ;[EINVAL]: An invalid argument was given. Most likely ''old_address'' was not page aligned. ;[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. ;[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 ''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. 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. (''Modern Operating Systems'' by Andrew S. Tannenbaum, ''Inside Linux'' by Randolf Bentson, ''The Design of the UNIX Operating System'' by Maurice J. Bach.)
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mremap(2)
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