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_get_info — query typed memory information (ADVANCED REALTIME)

SYNOPSIS

       #include <sys/mman.h>

       int posix_typed_mem_get_info(int fildes,
           struct posix_typed_mem_info *info);

DESCRIPTION

       The   posix_typed_mem_get_info()   function   shall   return,   in  the  posix_tmi_length  field  of  the
       posix_typed_mem_info structure pointed to by info, the maximum length which may be successfully allocated
       by the typed memory object designated by fildes.  This maximum length shall take into  account  the  flag
       POSIX_TYPED_MEM_ALLOCATE  or  POSIX_TYPED_MEM_ALLOCATE_CONTIG  specified  when  the  typed  memory object
       represented by fildes was opened. The maximum length is dynamic; therefore, the value returned  is  valid
       only while the current mapping of the corresponding typed memory pool remains unchanged.

       If  fildes represents a typed memory object opened with neither the POSIX_TYPED_MEM_ALLOCATE flag nor the
       POSIX_TYPED_MEM_ALLOCATE_CONTIG  flag  specified,  the  returned  value  of   info->posix_tmi_length   is
       unspecified.

       The posix_typed_mem_get_info() function may return additional implementation-defined information in other
       fields of the posix_typed_mem_info structure pointed to by info.

       If the memory object specified by fildes is not a typed memory object, then the behavior of this function
       is undefined.

RETURN VALUE

       Upon  successful  completion,  the  posix_typed_mem_get_info() function shall return zero; otherwise, the
       corresponding error status value shall be returned.

ERRORS

       The posix_typed_mem_get_info() function shall fail if:

       EBADF  The fildes argument is not a valid open file descriptor.

       ENODEV The fildes argument is not connected to a memory object supported by this function.

       This function shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       An application that needs to allocate a block of typed memory with length dependent upon  the  amount  of
       memory  currently  available must either query the typed memory object to obtain the amount available, or
       repeatedly invoke mmap() attempting to guess an appropriate length. While the latter method  is  existing
       practice  with  malloc(),  it is awkward and imprecise. The posix_typed_mem_get_info() function allows an
       application to immediately determine available memory. This is particularly important  for  typed  memory
       objects  that  may  in  some  cases  be  scarce resources. Note that when a typed memory pool is a shared
       resource, some form of mutual-exclusion or synchronization may be required while typed  memory  is  being
       queried and allocated to prevent race conditions.

       The  existing fstat() function is not suitable for this purpose. We realize that implementations may wish
       to provide other attributes of typed memory objects (for example, alignment requirements, page size,  and
       so  on).   The  fstat()  function  returns a structure which is not extensible and, furthermore, contains
       substantial information that is inappropriate for typed memory objects.

FUTURE DIRECTIONS

       None.

SEE ALSO

       fstat(), mmap(), posix_typed_mem_open()

       The Base Definitions volume of POSIX.1‐2017, <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 .

       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_GET_INFO(3POSIX)