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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.

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 .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                          POSIX_TYPED_MEM_OPEN(3POSIX)