MMAP (2)
map or unmap files or devices into memory
SYNOPSIS
#include <unistd.h>
#include <sys/mman.h>
#ifdef _POSIX_MAPPED_FILES
void * mmap(void * start , size_t length , int prot
, int flags , int fd , off_t offset );
int munmap(void * start , size_t length );
#endif
DESCRIPTION
The
mmap
function asks to map
length
bytes starting at offset
offset
from the file (or other object) specified by
fd
into memory, preferably at address
start .
This latter address is a hint only, and is usually specified as 0.
The actual place where the object is mapped is returned by
mmap .
The
prot
argument describes the desired memory protection. It has bits
PROT_EXEC
PROT_READ
PROT_WRITE
PROT_NONE
Pages may not be accessed.
The
flags
parameter specifies the type of the mapped object, mapping options and
whether modifications made to the mapped copy of the page are private to
the process or are to be shared with other references. It has bits
MAP_FIXED
Do not select a different address than the one specified.
If the specified address cannot be used,
mmap
will fail. If MAP_FIXED is specified,
start
must be a multiple of the pagesize. Use of this option is discouraged.
MAP_SHARED
Share this mapping with all other processes that map this object
MAP_PRIVATE
Create a private copy-on-write mapping.
You must specify exactly one of MAP_SHARED and MAP_PRIVATE.
The above three flags are described in POSIX.1b (formerly POSIX.4).
Linux also knows about MAP_DENYWRITE, MAP_EXECUTABLE and
MAP_ANON(YMOUS).
The
munmap
system call deletes the mappings for the specified address range, and
causes further references to addresses within the range to generate invalid
memory references.
RETURN VALUE
On success,
mmap
returns a pointer to the mapped area.
On error, MAP_FAILED (-1) is returned, and
errno
is set appropriately.
On success,
munmap
returns 0, on failure -1, and
errno
is set (probably to EINVAL).
ERRORS
EBADF
fd
is not a valid file descriptor (and MAP_ANONYMOUS was not set).
EACCES
MAP_PRIVATE was asked, but
fd
is not open for reading. Or MAP_SHARED was asked and PROT_WRITE is set,
fd
is not open for writing.
EINVAL
We don't like
start
or
length
or
offset .
(E.g., they are too large, or not aligned on a PAGESIZE boundary.)
ETXTBUSY
MAP_DENYWRITE was set but the object specified by
fd
is open for writing.
EAGAIN
The file has been locked, or too much memory has been locked.
ENOMEM
CONFORMING TO
SVr4, POSIX.1b (formerly POSIX.4), 4.4BSD. Svr4 documents additional
error codes ENXIO and ENODEV.
SEE ALSO
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