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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 .