Originální popis anglicky:
mremap - re-map a virtual memory address
Návod, kniha: Linux Programmer's Manual
#include <unistd.h>
#include <sys/mman.h>
void * mremap(void *old_address, size_t old_size
, size_t new_size, unsigned long flags);
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.
- MREMAP_MAYMOVE
- indicates if the operation should fail, or change the
virtual address if the resize cannot be done at the current virtual
address.
On success
mremap returns a pointer to the new virtual memory area. On
error, the value
MAP_FAILED (that is, (void *) -1) is returned, and
errno is set appropriately.
- EAGAIN
- The memory segment is locked and cannot be re-mapped.
- 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.
- EINVAL
- An invalid argument was given. Most likely
old_address was not page aligned.
- 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.
With current glibc includes, in order to get the definition of
MREMAP_MAYMOVE, you need to define _GNU_SOURCE before including
<sys/mman.h>.
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.
brk(2),
getpagesize(2),
mmap(2),
sbrk(2),
malloc(3),
realloc(3)
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.)
