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mremap(2) [netbsd man page]

MREMAP(2)						      BSD System Calls Manual							 MREMAP(2)

mremap -- re-map a virtual memory address LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/mman.h> void * mremap(void *oldp, size_t oldsize, void *newp, size_t newsize, int flags); DESCRIPTION
The mremap() function resizes the mapped range (see mmap(2)) starting at oldp and having size oldsize to newsize. The following arguments can be OR'ed together in the flags argument: MAP_ALIGNED(n) The allocation should be aligned to the given boundary, i.e. ensure that the lowest n bits of the address are zero. The parameter n should be the base 2 logarithm of the desired alignment (e.g., to request alignment to 16K, use 14 as the value for n). The alignment must be equal to or greater than the platform's page size as returned by sysconf(3) with the _SC_PAGESIZE request. MAP_FIXED newp is tried and mremap() fails if that address can't be used as new base address for the range. Otherwise, oldp and newp are used as hints for the position, factoring in the given alignment. RETURN VALUES
mremap() returns the new address or MAP_FAILED, if the remap failed. COMPATIBILITY
The semantics of mremap() differ from the one provided by glibc on Linux in that the newp argument was added and a different set of flags are implemented. SEE ALSO
mmap(2), munmap(2) HISTORY
The mremap() system call appeared in NetBSD 5.0. It was based on the code that supports mremap() compatibility for Linux binaries. BSD
February 14, 2008 BSD

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MREMAP(2)						     Linux Programmer's Manual							 MREMAP(2)

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 seg- ment 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 "Segmentation fault." Some address in the range 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. 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. (Modern Operating Systems by Andrew S. Tannenbaum, Inside Linux by Ran- dolf Bentson, The Design of the UNIX Operating System by Maurice J. Bach.) Linux 1.3.87 1996-04-12 MREMAP(2)
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