POSIX_TYPED_MEM_GET_INFO(3P)                        POSIX Programmer's Manual                       POSIX_TYPED_MEM_GET_INFO(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult 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() attempt-
       ing to guess an appropriate length. While the latter method is existing practice with malloc(), it is awkward and  impre-
       cise.  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() func-
       tion 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                  POSIX_TYPED_MEM_GET_INFO(3P)