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
       IEEE Std 1003.1-2001, <sys/mman.h>

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .