POSIX_TYPED_MEM_OPEN
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
posix_typed_mem_open
--- open a typed memory object
(
ADVANCED REALTIME)
SYNOPSIS
#include <sys/mman.h>
int posix_typed_mem_open(const char *name, int oflag, int tflag);
DESCRIPTION
The
posix_typed_mem_open()
function shall establish a connection between the typed memory object
specified by the string pointed to by
name
and a file descriptor. It shall create an open file description that
refers to the typed memory object and a file descriptor that refers to
that open file description. The file descriptor shall be allocated as
described in
Section 2.14,
File Descriptor Allocation
and can be used by other functions to refer to that typed
memory object. It is unspecified whether the name appears in
the file system and is visible to other functions that take
pathnames as arguments. The
name
argument conforms to the construction rules for a pathname, except that
the interpretation of
<slash>
characters other than the leading
<slash>
character in
name
is implementation-defined, and that the length limits for the
name
argument are implementation-defined and need not be the same as the
pathname limits
{PATH_MAX}
and
{NAME_MAX}.
If
name
begins with the
<slash>
character, then processes calling
posix_typed_mem_open()
with the same value of
name
shall refer to the same typed memory object. If
name
does not begin with the
<slash>
character, the effect is implementation-defined.
Each typed memory object supported in a system shall be identified by a name
which specifies not only its associated typed memory pool, but also the
path or port by which it is accessed. That is, the same typed memory
pool accessed via several different ports shall have several different
corresponding names. The binding between names and typed memory objects
is established in an implementation-defined manner. Unlike shared
memory objects, there is no way within POSIX.1-2008 for a program to create a
typed memory object.
The value of
tflag
shall determine how the typed memory object behaves when subsequently
mapped by calls to
mmap().
At most, one of the following flags defined in
<sys/mman.h>
may be specified:
- POSIX_TYPED_MEM_ALLOCATE
-
Allocate on
mmap().
- POSIX_TYPED_MEM_ALLOCATE_CONTIG
-
Allocate contiguously on
mmap().
- POSIX_TYPED_MEM_MAP_ALLOCATABLE
-
Map on
mmap(),
without affecting allocatability.
If
tflag
has the flag POSIX_TYPED_MEM_ALLOCATE specified, any subsequent call to
mmap()
using the returned file descriptor shall result in allocation and
mapping of typed memory from the specified typed memory pool. The
allocated memory may be a contiguous previously unallocated area of the
typed memory pool or several non-contiguous previously unallocated
areas (mapped to a contiguous portion of the process address space). If
tflag
has the flag POSIX_TYPED_MEM_ALLOCATE_CONTIG specified, any subsequent
call to
mmap()
using the returned file descriptor shall result in allocation and
mapping of a single contiguous previously unallocated area of the typed
memory pool (also mapped to a contiguous portion of the process address
space). If
tflag
has none of the flags POSIX_TYPED_MEM_ALLOCATE or
POSIX_TYPED_MEM_ALLOCATE_CONTIG specified, any subsequent call to
mmap()
using the returned file descriptor shall map an application-chosen area
from the specified typed memory pool such that this mapped area becomes
unavailable for allocation until unmapped by all processes. If
tflag
has the flag POSIX_TYPED_MEM_MAP_ALLOCATABLE specified, any subsequent
call to
mmap()
using the returned file descriptor shall map an application-chosen area
from the specified typed memory pool without an effect on the
availability of that area for allocation; that is, mapping such an
object leaves each byte of the mapped area unallocated if it was
unallocated prior to the mapping or allocated if it was allocated prior
to the mapping. Appropriate privileges to specify the
POSIX_TYPED_MEM_MAP_ALLOCATABLE flag are implementation-defined.
If successful,
posix_typed_mem_open()
shall return a file descriptor for the typed memory object.
The open file description is new, and therefore the file descriptor
shall not share it with any other processes. It is unspecified whether
the file offset is set. The FD_CLOEXEC file descriptor flag associated
with the new file descriptor shall be cleared.
The behavior of
msync(),
ftruncate(),
and all file operations other than
mmap(),
posix_mem_offset(),
posix_typed_mem_get_info(),
fstat(),
dup(),
dup2(),
and
close(),
is unspecified when passed a file descriptor connected to a typed
memory object by this function.
The file status flags of the open file description shall be set
according to the value of
oflag.
Applications shall specify exactly one of the three access mode values
described below and defined in the
<fcntl.h>
header, as the value of
oflag.
- O_RDONLY
-
Open for read access only.
- O_WRONLY
-
Open for write access only.
- O_RDWR
-
Open for read or write access.
RETURN VALUE
Upon successful completion, the
posix_typed_mem_open()
function shall return a non-negative integer representing the
file descriptor. Otherwise, it shall return -1 and set
errno
to indicate the error.
ERRORS
The
posix_typed_mem_open()
function shall fail if:
- EACCES
-
The typed memory object exists and the permissions specified by
oflag
are denied.
- EINTR
-
The
posix_typed_mem_open()
operation was interrupted by a signal.
- EINVAL
-
The flags specified in
tflag
are invalid (more than one of POSIX_TYPED_MEM_ALLOCATE,
POSIX_TYPED_MEM_ALLOCATE_CONTIG, or POSIX_TYPED_MEM_MAP_ALLOCATABLE is
specified).
- EMFILE
-
All file descriptors available to the process are currently open.
- ENFILE
-
Too many file descriptors are currently open in the system.
- ENOENT
-
The named typed memory object does not exist.
- EPERM
-
The caller lacks appropriate privileges to specify the
POSIX_TYPED_MEM_MAP_ALLOCATABLE flag in the
tflag
argument.
The
posix_typed_mem_open()
function may fail if:
- ENAMETOOLONG
-
The length of the
name
argument exceeds
{_POSIX_PATH_MAX}
on systems that do not support the XSI option
or exceeds
{_XOPEN_PATH_MAX}
on XSI systems,
or has a pathname component that is longer than
{_POSIX_NAME_MAX}
on systems that do not support the XSI option
or longer than
{_XOPEN_NAME_MAX}
on XSI systems.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.14,
File Descriptor Allocation,
close(),
dup(),
exec,
fcntl(),
fstat(),
ftruncate(),
mmap(),
msync(),
posix_mem_offset(),
posix_typed_mem_get_info(),
umask()
The Base Definitions volume of POSIX.1-2017,
<fcntl.h>,
<sys_mman.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
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